A systematic review of the avian antibody (IgY) therapeutic effects on human bacterial infections over the decade

Abstract

The overuse of antibiotics worldwide, especially during the Coronavirus pandemic, has raised concerns about the rise of antibiotic resistance and its side effects. Immunoglobulin Y, a natural protein that specifically targets foreign antigens, holds promise as a potential therapeutic option, particularly for individuals with sensitive immune systems. Despite numerous studies on IgY, the optimal administration method, effective dose, target antigen, and potential side effects of this antibody remain areas of active research and challenge. This review selected and evaluated articles published in the last ten years from databases such as PubMed and Science Direct with appropriate keywords discussing the therapeutic effects of immunoglobulin Y in human infections in vivo. Out of all the reviewed articles, 35 articles met the inclusion criteria. The results showed that the specific antibody against dental, respiratory, and skin infections has an acceptable effectiveness. In contrast, some infections, such as neurological infections, including tetanus and botulism, still need further investigation due to the short survival time of mice. On the other hand, reporting side effects such as antibody-dependent enhancement in some infections limits its use.

Introduction

Despite their efficacy in treating bacterial infections, antibiotics can lead to side effects such as allergic reactions and antibiotic resistance (AR). AR poses a significant global challenge, particularly given the increased antibiotic consumption during the COVID-19 pandemic. According to the CDC’s 2019 Antibiotic Resistance Threats Report, this issue results in a devastating 1.27 million deaths annually worldwide. Apart from the high mortality rate, these infections also incur substantial costs for governments. The organization has proposed several solutions to address this issue, including infection prevention and control, improved data collection, responsible use of antibiotics, vaccination, alternative treatments, and addressing environmental pollution caused by antibiotics.

The use of antibiotics may lead to the disruption of the human microflora and the substitution of pathogenic bacteria [1].

As of June 2019, only seven unconventional products have advanced to phase 3 clinical trials. Notable alternative treatment and prevention options include vaccines, antibodies, bacteriophages, and fecal microbiota transplant/live biotherapeutics.

Antibodies are proteins naturally produced by the body in response to foreign agents, such as microbes. Vaccines, however, trigger the production of antibodies, which slows down the response [1]. The primary role of antibodies in combating various antigens is to neutralize them through structural changes or by binding to epitopes [2].

Under uncontrolled conditions, the binding of antibodies can lead to a severe cytokine cascade and cause severe damage [3].

The initial case demonstrating the enhancement of bacterial infection by antibodies in Vibrio cholerae indicated that these animals were more susceptible to intraperitoneal infection [4].

In laboratory models, antibodies targeting Streptococcus pneumoniae and Acinetobacter baumannii have been found to enhance bacteria’s attachment to tissues [5, 6].

Furthermore, human cohort studies support this finding in the case of Pseudomonas aeruginosa and Neisseria gonorrhea infections [7, 8].

Specifically, IgG specific to the gonococcal reversibly modifiable protein (Rmp, protein III) has the potential to inhibit complement killing [8].

Despite numerous studies on IgY, many questions still need to be answered, including its effectiveness and the determination of the appropriate dosage for in vivo applications. This study explored this antibody’s effectiveness and suitable dosage for the treatment and potential prevention of bacterial infections in both animal models and clinical trials.

Materials and methods

Search study

In this review, a comprehensive search was conducted using the keywords [Chicken IgY OR immunoglobulin Y OR egg yolk antibody] AND [Bacteria* infect*] across the Pubmed, Pubmed Central (PMC), and Science Direct databases. Additionally, relevant research articles within the fields of immunology and microbiology were identified using the keywords [Chicken IgY OR immunoglobulin Y OR egg yolk antibody] AND [Bacterial infection] specifically within the Science Direct database.

Inclusion and exclusion criteria

The inclusion criterion for this study involved selecting articles that focused on population challenges in mouse and human subjects (in vivo studies) from the past 10 years, specifically from March 2013 to February 2023. Articles published before 2013, in vitro studies, non-English reports, gray literature, and nonhuman infections were excluded from the analysis.

Results

Oral infections

Tooth decay is a slow-progressing disease caused by the acidic byproducts of bacteria [9]. One of the primary culprits behind this condition is the colonization of teeth by cariogenic bacteria, notably Streptococcus mutans, which can be transmitted from mother to baby in early life [10].

Given the potential complications associated with dental vaccines in humans, one practical approach to addressing this issue may involve the use of passive immune agents, such as IgY [11, 12].

In a rat study, the impact of a 2% IgY gel on S. mutans at a concentration of 10¹¹ CFU/ml over 78 days was investigated. The study’s findings indicate that the utilization of a gel containing IgY led to a decrease in the attachment of bacteria to the tooth surface [13].

Periodontitis is a significant oral disease that arises from an imbalance of microbes in the oral ecosystem, leading to the proliferation of pathogenic bacteria and subsequent destruction of the tooth’s supporting tissues. Among the 50 identified effective species, Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis are considered to be the primary culprits responsible for juvenile periodontitis [14, 15].

Treatment of this infection with antimicrobial agents, in addition to its side effects, may lead to an increase in AR [16].

In a clinical trial involving 60 patients divided into three groups, each receiving IgY, chlorhexidine 2%, or a placebo for four weeks, significant reductions in red-complex bacteria and bleeding on probing were observed in the IgY and chlorhexidine groups. However, no significant differences were found compared to the placebo group. Overall, analysis of clinical parameters did not reveal significant differences between the groups. These results suggest that IgY may be used as a supplementary mouthwash along with Scaling and root planing (SRP) for the treatment of P. gingivalis periodontitis infection. Notably, no side effects were reported during the study, indicating the potential for long-term use, particularly among sensitive populations such as children and pregnant women [17].

Another clinical study of 64 periodontitis patients in two placebo groups and a group treated with IgY against P. gingivalis in the form of lozenges containing 12 mg of IgY powder for eight weeks showed significant differences in the reduction in gingival bleeding index (GBI) and the cell count of P. gingivalis in the intervention group compared to the placebo group. In this clinical trial, similar to the previous trial, no side effects were observed as a result of IgY treatment. IgY is more effective than other inhibitors because of its high affinity for bacterial antigens and because of its quick and easy movement to subgingival pockets to inhibit Porphyromonas [18].

The differences observed could be attributed to the delivery system, limited antibody penetration, short treatment duration, and the use of the specific antigen gingipain instead of the entire bacterium. A study conducted in Japan demonstrated that extending the treatment duration from 4 to 8 weeks led to a significant reduction in infection incidence, PD, GBI, and the number of Porphyromonas.

In a study on periodontitis and halitosis caused by Fusobacterium nucleatum, the impact of 200 microliters of IgY on 100 microliters of bacteria at a concentration of 10⁸ CFU/ml was examined in rats over a four-week treatment period. The study revealed that the growth of bacteria and halitosis significantly decreased in response to the high antibody dose (40 mg/ml). Furthermore, a notable difference was observed in the levels of IL-6 and TNF cytokines. Another noteworthy finding of this study was the improvement in periodontal damage repair and reduction in alveolar bone loss [19].

Microbial plaque accumulation around the gingival sulcus can lead to gingivitis, a condition that may be caused by Provetella intermedia, an anaerobic Gram-negative bacterium [20, 21]. In a recent study, it was noted that the growth of this bacterium can be dose-dependently inhibited by specific IgY at concentrations ranging from 1 to 20 mg/ml. Furthermore, in an experiment involving rats, the consumption of IgY at a concentration of 20 mg/ml for 15 days was found to effectively protect the gums against Provetella bacteria at a concentration of 10¹¹ CFU ml⁻¹, significantly reducing the gingival index (GI), plaque index (PI), and bleeding on probing (BOP), as well as improving inflammation and gum damage in the rats [22].

According to the findings, IgY has demonstrated potential in the prevention of tooth decay by inhibiting the colonization of cariogenic agents, notably S. mutans. Moreover, it has exhibited promise in the management of periodontitis by reducing both gum bleeding and the population of P. gingivalis bacteria.

Skin infections

Bacterial infections, particularly P. aeruginosa, are a common cause of high mortality in burn patients. The widespread development of AR has presented significant challenges in effectively treating burn infections [23, 24].

A study conducted in Iran examined the impact of IgY on the PcrV gene of P. aeruginosa in burn infections. The findings revealed that administering 1 mg and 0.5 mg of IgY for three days enhanced the management of P. aeruginosa infection in the burnt skin of mice, which had a concentration of 3–5 × 10⁷ CFUs. The intervention group demonstrated a 22%–33% survival rate, while no mice in the control group survived [25].

In another study, similar to the previous one, researchers focused on the impact of the IgY antibody on OprF in P. aeruginosa. The results revealed that when mice were treated with two doses of 0.1–10 mg of IgY, up to 25% of the subjects survived. However, when administered intravenously with 0.5 to 1 mg of IgY, the survival rate increased to 50%. In the prophylaxis group, the use of 1 mg of IgY subcutaneously or 0.5 mg intravenously led to an 87.5% increase in the survival of infected mice. In contrast, in the control group, no mice survived after wound infection [26].

In a study involving a mouse model with P. aeruginosa burn wounds, 4 × 10⁸ CFUs and 500 μg of IgY were intravenously injected into the burned skin at three subsequent doses. The use of Anti-FlaB IgY resulted in 100% protection in the immunized mice. The bacterial load and survival rate of the mice were significantly higher compared to the other groups [27].

The findings from the studies above indicate that intravenous administration yields better results than subcutaneous injection. It is worth noting that the FlaA antigen unexpectedly resulted in increased mortality, possibly due to antibody-dependent enhancement (ADE), underscoring the importance of selecting a suitable antigen to prevent undesired complications.

Respiratory infections

Despite advances in medicine, pneumonia continues to pose a significant threat, with a high mortality rate. Gram-negative bacteria, particularly P. aeruginosa, are known to play a crucial role in these infections [28]. In a study involving mice infected with P. aeruginosa pneumonia, the administration of 2 × 10⁷ CFU of bacteria preincubated with anti-PcrV IgY at concentrations of 0.1 and 1 mg for one week resulted in a noteworthy 71.42% survival rate among the immunized mice. In contrast, no mice in the control group survived [25].

In another study, BalB/C mice previously infected intranasally with 40λ of P. aeruginosa received 20 λ of a specific IgY. The results indicated a significant reduction in bacterial load and moderation of inflammation, as evidenced by decreased levels of cytokines TNF-α and IL-1β.

The use of IgY gargling may mitigate damage and complications from pulmonary infection in cystic fibrosis patients. The bacterial load 24 h after treatment was notably lower in the IgY group. This study suggests that the therapeutic effect of IgY 6 h after infection was less effective than its preventive effects. Therefore, this approach shows promise in reducing the impact of this infection in cystic fibrosis patients [29].

In cystic fibrosis, there is a continuous inflammatory response due to the formation of Pseudomonas biofilms, which can be reduced by suppressing the respiratory burst triggered by IgY. Even at the lowest concentration (0.1%–0.5%), there was a significant increase in the formation of clamps and phagocytosis of bacteria by Polymorphonuclears (PMNs). This led to a decrease in bacterial survival from 70% to 89% compared to the control group [30, 31].

In contrast to previous studies in Iran on the impact of IgY antibodies produced against various antigens of A. baumannii, such as Omp-34, Omp-A, and inactive whole cells, the survival rates were 75% in the IgY-A and IgY WC (whole cell) groups. None of the mice in the other group survived. Surprisingly, the presence of IgY resulted in ADE, leading to increased mouse infection and higher Acinetobacter load in the lungs, spleen, and blood, possibly due to the release of bacterial capsular antigens that interacted with the antibody. However, this issue can be addressed by identifying and designing cloned antigens without ADE-causing epitopes. In this study, 40 μl of antibody was used to inhibit bacteria at a concentration of 2.04 × 10⁷ CFU in a mouse model.

In studies examining the effects of protein antigens on bacterial activity in mice, it was found that these antigens provide stronger immunity compared to inactive whole cells. The primary antibacterial mechanism of these antigens is likely the inhibition of bacterial attachment [32, 33].

In an another study on the impact of IgY-BAP on A. baumannii pneumonia, a notable decrease in bacterial load and biofilm formation was observed in comparison to the control group. The survival rate of the mice treated with IgY-BAP was reported to be 83%. The treatment involved the administration of 40 μl of antibody to combat a concentration of 1.7 × 10⁸ CFU in a mouse model intranasally for 14 days [34].

Another study focusing on a mouse model of P. aeruginosa pneumonia revealed that the minimum effective dose to inhibit infection was 50 μg/ml. The inhibitory effect of IgY against FlaA and FlaB was reported to range from 17.6% to 36.3%, depending on the bacterial strain. Moreover, this antibody demonstrated complete protection and promoted the survival of the mice.

In this experiment, mice were intranasally administered 2 × 10⁷ CFUs of bacteria along with 500 μg of IgY for one week, followed by two doses of 250 μg of antibody. According to the results, IgY against Fla-B exhibited greater immunogenicity compared to other IgYs [27].

In a research study, 24 pigs were intrabronchially examined with 10 mg/ml IgY against P. aeruginosa at a concentration of 10⁹ CFU/ml. They received a second dose of the antibody 27 h later. The findings indicated that the bacterial load remained unchanged in the group that received the intervention, suggesting that the amount of antibody and the method of administration may be suitable for achieving these results. In this investigation, 20 ml of Pseudomonas was treated with 10 mg/ml IgY at a concentration of 10⁹ CFU/ml, followed by two booster doses over four weeks via intra bronchial (BAL) administration [35].

In a study examining the impact of IgY targeting omp-34 on A. baumannii over 72 hours, it was reported that the survival rate of the mice ranged from 88.33% to 100%. However, these mice also succumbed after 72 hours, similar to the control group. Notably, no reduction in bacterial load was observed in the specific antibody group compared to the control group [36].

Based on these findings, the intranasal administration of IgY proved to be more effective than the intra BAL route. Additionally, the specific antibody against Bap in A. baumannii infections demonstrated greater efficacy compared to the antibodies targeting OmpA or Omp34. Furthermore, it was noted that the antibody, when modulating inflammation, could exhibit bactericidal effects while mitigating the undesired side effects on the immune system, particularly in cystic fibrosis patients.

Neurological infections

Botulism is a dangerous infection of the nervous system caused by various neurotoxins that lead to neuromuscular paralysis. Due to its high infectivity and potential as a bioterrorist agent, botulism poses a severe threat that necessitates the development of new treatment methods [37, 38].

A study conducted in China utilized IgY against the BoNT/B neurotoxin and found that this specific antibody was effective in protecting against botulism when administered at a concentration of 50–100 ng per mouse intraperitoneally, 1.5 hours after infection with 0.0873 ng of botulinum neurotoxin. In contrast to the control group, all immunized mice survived significantly, but they died after 3 hours. These results underscore the importance of dosage, route of administration, and prompt treatment with IgY in determining its effectiveness [39].

Tetanus is a deadly disease caused by the production of exotoxin by Clostridium tetani. The significance of vaccination for disease prevention became evident, especially in the mid-20th century. However, due to the waning effectiveness of the vaccine in old age, mortality rates remain high in developing countries [40, 41].

A study conducted on a mouse model examined the effect of IgY against tetanus toxin. The results indicated that purified IgY can neutralize tetanus toxin at a concentration of 100 MLD, and repeated intravenous injections enhance its effectiveness [42].

According to the referenced studies, when administered intraperitoneally immediately after infection, the antibody can neutralize botulinum neurotoxin. However, if this administration is delayed by more than 3 hours, it will not reduce mortality. In the case of tetanus, repeated intravenous doses of antibodies could prove to be effective.

Gastrointestinal infections

Cholera, a longstanding gastrointestinal infection caused by V. cholerae, remains widespread, particularly in impoverished nations. Although antibiotics have been effective in treating the infection, the adverse side effects associated with their use have prompted the search for alternative treatment and prevention methods [43, 44].

A study examining the impact of anti-LPS IgY on V. cholera revealed that even small amounts, around 2.5 μg, can confer 100% immunity against the infectious dose of MLD (2 × 10⁸ CFU) of V. cholera [45].

In a study investigating the impact of IgY on V. cholera toxin B, researchers noted a significantly higher survival rate in the IgY-treated group compared to the control group (66%). However, administering antibodies 2 hours prior to bacterial inoculation did not result in prophylaxis. During the experiment, mice were exposed to 50 μl of V. cholerae suspension at concentrations of 4 × 10⁸ and 1 × 10⁹ CFU/ml, followed by 50 μl of CTB-IgY at a concentration of 1 mg/ml [46].

Another study conducted in Iran on cholera revealed that antibodies targeting recombinant antigens CtxB, OmpW, and TcpA in mice infected with V. cholera significantly boosted the immune response. Mice in this study were treated with 5 × 10⁹ CFU/ml bacteria and antibodies (100 μg/50 μl) in two doses. The results indicated that 550 μg/ml of IgY against CtxB, either alone or in combination with OmpW, could inhibit the cytotoxic effects of cholera toxin. This effect was further enhanced when combined with TcpA (850 μg/μl), while specific antibodies against OmpW and TcpA alone did not have an effect. Additionally, the survival rate of mice in the intervention group, compared to the control group, ranged from 20% to 60%. Interestingly, the group that received TcpA-IgY exhibited a more significant survival rate (60%) compared to the other intervention groups [47].

The effectiveness of IgY against Vibrio LPS has been demonstrated to provide superior survival and protection compared to subunit antigens such as CtxB, OmpW, and TcpA. Even a small quantity of this antibody has been found to confer 100% immunity against these bacteria. However, a study on IgY prophylaxis against ToxB showed that it does not have an inhibitory effect on the disease 2 hours after infection.

Research on the impact of antibodies on Salmonella typhimurium revealed a 40% survival rate compared to the control group, which is a significant finding. Specific IgYs were shown to offer sufficient protection against S. typhimurium in a mouse model while also inhibiting the production of pro-inflammatory cytokines such as TNF-α and IL-10 from the intestinal mucosa [48].

In the case of Enterotoxigenic coli infection, specific IgYs at medium and high doses of up to 5 mg/ml effectively alleviated clinical symptoms of bacteria at a dose of 1 × 10⁷ CFU. However, the serum levels of indicators such as Aspartate Aminotransferase (AST) were similar to those in the control group. It also induced immune modulation, but there was no significant difference in the survival rate of mice between the antibody-treated and untreated groups. Oral administration of specific IgY was found to reduce damage and mitigate the histopathology of mice [49].

In a similar study on the effects of enterotoxins from this bacterium on mouse challenge, researchers observed that, unlike LT, IgY, which acts against Bap fusion peptides, has a neutralizing effect on ST coli enterotoxins [50].

After the challenge with Shiga toxin 2e, mice developed complete resistance to 2.5, 5, and 10-fold the LD-50 concentration when treated with immunoglobulin IgY at a concentration of 1.25 mg/ml, demonstrating its neutralization effect. However, three out of five mice that received a 10-fold concentration of bacteria died after a more extended period than the control group [51]. This suggests that the antibody may be more effective at low toxin concentrations, particularly during the early stages of infection.

In vivo studies on Helicobacter pylori against the bacteria and the urease subunit alone and in combination can have 50%, 70%, and 83.3% clearance rates of H. pylori, which is 18% greater than that of routine omeprazole and clarithromycin treatment (66.7%). In this study, a concentration of 10⁸ CFU/ml bacteria was used [52].

In another investigation involving Helicobacter, the use of IgY against VacA resulted in a notable reduction in serum IgG antibody levels, gastric histological alterations, and bacterial presence in comparison to the control group. The study involved the daily administration of 290 mg/l antibodies to mice for two weeks and the application of 0.2 ml of Helicobacter at a concentration of 10⁸ CFU three times a week for one month [53].

Clostridium difficile is a Gram-positive bacillus commonly found in nature. Its spores can lead to diarrhea, particularly in patients undergoing antibiotic treatment such as clindamycin [54].

In a study involving mice infected with this bacterium, the mice were administered 6 × 10⁷ bacterial spores and received five doses of antibody at varying concentrations between 50 and 200 μg before and after inoculation. The study, which utilized ELISA and western blot analyses, revealed that there was no cross-reaction between IgY and normal intestinal flora or mouse intestinal cells. Furthermore, the consumption of 600 μg of antibody was found to be effective in preventing the onset of Clostridium difficile infection (CDI) and bacterial colonization. Interestingly, simultaneous consumption of the antibody with vancomycin was observed to reduce the recurrence of infection [55].

Based on the studies above, the therapeutic potential of specific IgY antibodies targeting CtxB, OmpW, and TcpA antigens showed promise. However, it did not have a preventive effect on the disease. For S. typhimurium and enterotoxigenic Escherichia coli bacteria, it resulted in disease improvement and immune system modulation. However, its efficacy was limited to low concentrations of Shiga toxin in E. coli infection. Specific antibodies against the entire H. pylori bacteria, urease, and VacA demonstrated significant effects.

Hospital infections

P. aeruginosa is a significant pathogen responsible for urinary tract infections, particularly in hospitalized patients. Its high AR has raised concerns at the World Health Organization [56, 57].

In a study involving mice infected with this pathogen, a specific antibody against bacterial infection was administered at a concentration of 20 mg/ml at levels of 5 × 10⁵ or 5 × 10⁷. The results demonstrated a significant reduction in bacterial load in the mouse bladder with this dosage. Additionally, the study found that the consumption of IgY 30 minutes prior to infection resulted in a significant decrease in bacterial load. Furthermore, the intervention group showed an absence of inflammation and inflammatory cytokines, indicating a high potential for treatment and prophylaxis [58].

One critical aspect of treating hospital infections is addressing infections that are resistant to antibiotics. For instance, Acinetobacter infections have become challenging to treat due to the increasing prevalence of carbapenem resistance [59].

In a study on pan-drug-resistant Acinetobacter baumanii pneumonia, researchers found that treating the infection with IgY significantly reduced pro-inflammatory cytokines compared to the control group [60].

Additionally, the entry of bacterial LPS into the bloodstream can be fatal for patients with severe trauma and burns. Therefore, it is crucial to find a solution to neutralize endotoxin. One effective treatment is IgY, which has been shown to neutralize LPS or enhance phagocytosis after enterogastric administration in mice [61, 62].

In a clinical study examining E. coli and Klebsiella pneumoniae bacteria with Extended Spectrum Beta Lactamases (ESBL) resistance patterns, it was found that the consumption of 70 ml of a specific IgY solution at a concentration of 0.18 mg/ml for 28 days led to the spontaneous elimination of bacteria in patients. Mild side effects were observed in both the control and intervention groups at similar rates (42% and 58%, respectively), with only one person experiencing severe nausea and vomiting. However, due to the small sample size in this study, these differences were not statistically significant [63].

Pseudomonas aeruginosa poses a significant threat in the intensive care unit (ICU) as it is a major cause of sepsis and septic shock [64, 65]. A study on the impact of IgY on the PilQ/PilA protein of P. aeruginosa in a rabbit sepsis model revealed that intravenous administration of this antibody led to a reduction in inflammatory mediator levels. However, its inhibitory effect was notably less than that of killed bacteria, possibly due to increased hydrophobicity, which in turn improved phagocytosis. Intravenous administration of IgY did not significantly impact survival, reduce inflammatory mediator levels, or decrease the bacterial load [66].

Another significant pathogen in antibiotic-resistant sepsis is A. baumannii, which has been linked to high mortality rates [67, 68].

In a study on the effect of IgY on Omp-34 in A. baumannii in a murine model of sepsis, it was reported that the survival rate of Acinetobacter in mouse serum containing a specific IgY was 64%. Unlike the control group, the treatment group exhibited a high bacterial load, underscoring the importance of this protein in protection against Acinetobacter infection [69].

The findings from these studies demonstrate that the IgY antibody is more effective against whole-killed bacteria compared to the P. aeruginosa PilQ/PilA protein. Furthermore, this particular antibody shows promise for treating and preventing antibiotic-resistant infections, particularly in trauma and severe burn patients.

Others

Vibrio vulnificus is a type of gram-negative bacterium that can lead to a range of infections, including skin wounds, soft tissue infections, and potentially fatal diseases like sepsis [70].

A study conducted in China demonstrated that IgY, which targets inactivated V. vulnificus bacteria, can significantly decrease the bacterial count in vivo compared to the control group. Administering a specific IgY 1 hour after infection was found to increase the survival rate of mice by 100%. Additionally, the study explored the use of this antibody for prophylaxis, revealing that intraperitoneal administration of the antibody 2 hours before bacterial inoculation can provide 100% protection.

In the current investigation, a concentration range of 0.5 to 2 mg/ml of IgY was employed for the treatment of bacteria at a density of 2 × 10⁶ CFU/ml. Noteworthy findings revealed a pronounced inhibitory impact on bacterial proliferation, coupled with a concurrent mitigation of inflammation and a reduction in bacterial load within the bloodstream [71].

In accordance with the findings above, the administration of antibodies within 1 hour postinfection demonstrates a notable enhancement in the treatment of infected mice. Furthermore, intraperitoneal administration of antibodies up to 2 hours prior to bacterial infection proves to be a highly effective preventive measure, boasting a 100% success rate in infection prevention.

Discussion and conclusion

New treatment methods, such as phage therapy, antimicrobial peptides, silver nanoparticles, bacteriocins, drug-conjugated antibodies, and photodynamic treatments, have emerged as alternative strategies to antibiotics [72].

In specific scenarios, the utilization of antibiotic adjuvants has the potential to diminish the quantity of antibiotics administered. For instance, the pterostilbene adjuvant has been shown to enhance the efficacy of polymyxin B [73].

The rise of widespread microbial resistance, particularly in hospitals, and the lack of discovery of new antibiotics pose significant threats to global health. Therefore, exploring new therapeutic approaches, such as antibodies, could offer a potential solution to this problem. In recent years, IgY has been mentioned as one of the alternative options in the treatment of various infections, for which different mechanisms have been considered.

IgY antibodies are effective in neutralizing bacterial pathogens by binding to surface antigens, preventing the bacteria from adhering to host cells. This mechanism is particularly useful in infections like Salmonella enterica and S. mutans [11, 74, 75].

IgY has the ability to neutralize bacterial toxins. For instance, in V. cholerae infections, IgY antibodies targeting cholera toxin can prevent the toxin’s harmful effects on intestinal epithelial cells, thus reducing the severity of diarrhea and fluid loss [46, 76].

While IgY itself does not activate the classical complement pathway (due to differences in its Fc region compared to mammalian IgG), it can still interact with the host immune system through other mechanisms. For instance, IgY has been shown to enhance phagocytosis in macrophages and neutrophils. It can facilitate the engulfment of bacterial pathogens through Fc receptor-mediated mechanisms. This is particularly useful in skin and respiratory infections, where rapid immune responses are needed to clear pathogens [48, 77].

Interestingly, IgY’s role in modulating the immune system is complex. While it lacks the ability to activate complement effectively, it may still promote inflammation through other pathways, such as cytokine modulation. This property is essential in certain infections, such as P. aeruginosa pneumonia, where the balance between effective pathogen clearance and excessive inflammation is critical. In these cases, IgY can modulate the immune response to avoid tissue damage [29].

In general, mechanisms such as inhibition of bacterial attachment, increased phagocytosis of pathogens by PMNs, modulation of the immune system, and ultimately neutralization of toxins are its most prominent mechanisms [78].

IgY can directly bind to bacterial surface antigens or virulence factors, weakening bacterial defenses and making them more susceptible to antibiotics. For instance, IgY targeting bacterial adhesion molecules can prevent biofilm formation, a major barrier to effective antibiotic treatment in infections caused by P. aeruginosa and Staphylococcus aureus. This synergistic effect can improve the efficacy of antibiotics like ciprofloxacin and vancomycin, particularly in biofilm-associated infections [79, 80].

By neutralizing specific bacterial toxins or interfering with bacterial adhesion and colonization, IgY can reduce the bacterial load, thereby allowing lower doses of antibiotics to be used. In a study on S. enterica, IgY in combination with amoxicillin significantly reduced bacterial load in a murine model compared to the antibiotic alone, demonstrating that IgY can enhance the effectiveness of antibiotics even at reduced doses [81].

Combination therapies involving IgY and antibiotics may reduce the likelihood of resistance development. Antibiotics target essential bacterial processes, while IgY provides a complementary mechanism by targeting surface antigens or toxins. This dual action reduces selective pressure on bacteria, potentially slowing the emergence of resistant strains. For instance, IgY targeting A. baumannii outer membrane proteins (Omp-34) enhanced the activity of colistin against resistant strains [79, 82].

This study identified 181 and 1912 articles published between 2013 and February 2023 in the PubMed and PMC databases, respectively. Additionally, 4363 research articles in immunology and microbiology were found in the Science Direct database, with only 35 original articles meeting the eligibility criteria for this study. These data are given in Fig. 1 as a PRISMA flow diagram.

The results of this study show that most of the in vivo studies have been done on mice and rats, and human studies have been done on P. gingivalis, E. coli, and K. pneumoniae infections. Studies of P. aeruginosa in addition to mice have also been conducted in two models, rabbits and porcine, as shown in Fig. 2.

According to this study, the therapeutic effects of IgY in vivo on oral and dental, skin, respiratory, nervous, and gastrointestinal and hospital infections have been carried out, as shown in Fig. 3.

Table 1 shows the type of bacterial infection, the pathogen, the type of antigen and the laboratory animal under study. According to this table, in most of the studies, genes and killed bacteria have been used to produce antibodies, and in a few cases, toxin, LPS, and bacterial spores have been used. However, as mentioned earlier, the use of some bacterial genes may have serious side effects, such as ADE, which should be noted. ADE is a phenomenon in which low levels of antibodies can worsen an infection. These antibodies can facilitate pathogen entry into host cells, which can increase pathogen replication. The incidence of ADE varies based on the pathogen, including the bacterial species [84, 85]. This may be more relevant for pathogens that utilize Fc receptor-mediated internalization, such as certain strains of S. aureus or Salmonella species. The occurrence of ADE in IgY therapies appears to be influenced by a variety of factors, such as the dose and the method used to administer the IgY.

Situations where the IgY concentration is too low to completely neutralize the pathogen but still high enough to promote bacterial entry may increase the likelihood of ADE. Additionally, how the IgY is administered (orally, under the skin, or directly into the bloodstream) can impact its stability and how readily it’s available in the body, potentially affecting the risk of ADE. Since IgY antibodies are primarily intended to neutralize bacterial antigens outside host cells, the higher hydrophobicity of IgY molecules facilitates the phagocytic function of immune components, and yet any facilitation of bacterial uptake could counteract the effects of IgY-based therapeutics [86]. In addition, it has been studied more for the treatment of pneumonia and gastrointestinal infections. The route of antibody administration has a great effect on its efficiency, which can be different based on the type of infection. So, in skin infections, intravenous injection, in respiratory infections, intranasal administration, or in nerve infections such as tetanus, intraperitoneal injection is considered the best route of antibody administration.

In general, the route of administration plays a crucial role in IgY’s therapeutic effectiveness across different infection types. For instance, in a murine model of pneumonia, intranasal IgY administration led to a significant reduction in bacterial load and inflammation, which was not observed with systemic administration [26]. On the other hand, intravenous administration is often preferred for systemic infections or skin infections, as it allows for rapid distribution of IgY antibodies throughout the body, providing broader protection. Oral and subcutaneous routes are also considered for gastrointestinal and skin infections.

The dose of IgY can also vary based on the type of infection, such that in gastrointestinal diseases, higher doses are required due to the difficult absorption of antibodies, while in respiratory, local, and then oral infections, lower doses of IgY are prescribed, respectively.

Another effective factor in the effectiveness of antibody administration is the time of administration of the antibody, so in the case of botulism, if it is used 3 hours later, it will not have an effect on neutralizing the toxin. Or, in the case of tetanus, it requires frequent doses.

Based on these results, the specific antibody against dental, respiratory, and skin infections has shown acceptable effectiveness. However, further investigation is needed for some infections, such as neurological infections, including tetanus and botulism, due to mice’s short survival time, as detailed in Table 2.

One limitation of this review article is the variation in IgY antibody production methods, extraction, and purification, which may impact the studies’ results. It is also important to explore the synergistic effect of this antibody with standard antibiotics, as this aspect has not been adequately studied in most infections. Other limitations include the lack of investigation into the mechanism of the host’s immune system response to these antibodies, their long-term effects, and the absence of clinical studies in this area. Ultimately, the findings of this study can guide the appropriate method of antibody administration and dosage, potential side effects, and serve as a foundation for future clinical studies.

Despite significant advancements in the development and application of IgY antibodies, several areas require further investigation to fully realize their therapeutic potential. A major challenge in IgY research is the lack of standardized production and purification protocols. Variations in the methods used to extract and purify IgY can lead to inconsistencies in antibody quality, affecting efficacy and reproducibility across studies.

Future research should prioritize the establishment of universally accepted protocols for IgY production to ensure consistent quality and reliability in both preclinical and clinical applications. While IgY is generally considered safe, the long-term effects of its use, particularly in vulnerable populations like children and immunocompromised individuals, remain underexplored. Research should focus on conducting extended in vivo studies and clinical trials to evaluate the safety, immunogenicity, and potential long-term impacts of repeated IgY administration.

Finally, while this review highlights the therapeutic potential of IgY, future research could focus on advanced technologies such as spatial sequencing and multimodal omics to deeply understand the mechanism of action of IgY, especially in complex infections such as botulism and tetanus [87, 88].

Author contributions

Zahra Esmaeili (Data curation [equal], Investigation [equal], Methodology [equal]), Sara Kamal Shahsavar (Methodology [equal], Software [equal], Visualization [equal]), and Kiarash Ghazvini (Conceptualization [equal], Project administration [equal], Supervision [equal]).

Conflict of interest

The authors are affiliated with Mashhad University of Medical Sciences.

Funding

The authors would like to acknowledge funding from the Mashhad University of Medical Sciences.

Data availability

The data that support the findings of this study are available on request from the corresponding author.

Ethics and consent statement

Not applicable.

Animal research statement

Not applicable.

References