https://orcid.org/0000-0002-6373-682X
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Matthew C Walsh, Yun Hee Jeong, Yongwon Choi, Response to Comment on “Mice Lacking the Purinergic Receptor P2X5 Exhibit Defective Inflammasome Activation and Early Susceptibility to Listeria monocytogenes”, The Journal of Immunology, Volume 206, Issue 4, February 2021, Pages 667–668, https://doi.org/10.4049/jimmunol.2001226
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As indicated in the letter by Rissiek et al., our article characterizing P2X5-dependent elements of the immune response to Listeria monocytogenes (1) employed a P2X5-deficient (P2X5−/−) mouse strain (B6;129S5-P2rx5tm1Lex/Ieg; MGI:5430769) that was generated by Lexicon Genetics using 129S5/SvEvBrd (129) background embryonic stem (ES) cells. Whereas we backcrossed P2X5−/− mice to the C57BL/6 background at least 10 times before using them for experiments, the very close proximity of the P2rx5 locus to Nlrp1a, Nlrp1b, and Nlrp1c loci suggests a high probability that mice carrying the P2X5−/− allele continue to harbor Nlrp1 passenger mutations associated with the 129 background (2). Indeed, having now analyzed RNA sequencing data generated from wild-type (WT) and P2X5−/− bone marrow–derived macrophages (BMMs), we find that P2X5−/− samples show dramatically reduced expression levels of Nlrp1a and Nlrp1c, compared with WT samples, but normal levels of Nlrp1b (Fig. 1). These findings are consistent with the presence of Nlrp1 passenger mutations from 129 ES cells in our backcrossed P2X5−/− mice (3). Therefore, observations we made with P2X5−/− mouse cells should be considered to have been made in the context of potential accompanying differences in NLRP1 function compared with experimentally paired WT control mouse cells. However, to be clear, we made no claim in our article that P2X5 regulates NLRP1 function or Nlrp1 gene expression, and although L. monocytogenes may trigger NLRP1 activation, it remains unclear whether NLRP1 plays any significant role in anti–L. monocytogenes immune responses (4, 5). It is possible that NLRP1 contributes to L. monocytogenes–induced immune responses, though we are not currently in a position to address whether differences in Nlrp1 genes impact susceptibility of P2X5−/− mice infected with L. monocytogenes. These questions will need to be addressed in the future, ideally with the use of tools that enable independent assessment of contributions by NLRP1 versus P2X5. In this regard, we recommend that future studies addressing the role of P2X5 in anti–L. monocytogenes immunity be performed using P2X5−/− mice newly derived from C57BL/6 background ES cells to dissect whether P2X5 acts alone or in concert with NLRP1.
