Abstract

The dynamics of the precipitation of labeled tracer hormones (human growth hormone, luteinizing hormone and follicle-stimulating hormone)-antibody complexes have been investigated utilizing rabbit antisera directed against the hormone and sheep anti-rabbit gamma globulin precipitating sera. Studies were performed in buffer alone and in the presence or absence of EDTA, varying quantities of normal human serum, heated human serum, a human euglobulin fraction and the serum supernatant remaining after precipitation, normal rabbit serum, and rabbit serum which had been frozen and thawed repeatedly. Both EDTA and normal human serum enhanced precipitation when added separately. The enhancement when both were present was greater than that due to either alone and was proportional to the amount of human serum added. The effect of human serum was reproduced by the euglobulin fraction; the serum supernatant had no effect. Heating the human serum inhibited this enhancement. Repeated freezing and thawing of the normal rabbit serum abolished the enhancement of precipitation due to normal rabbit serum. Addition of human serum with the precipitating antibody to standards reproduced the conditions found in samples. Unlabeled hormone added with the precipitating antisera had no effect. These results indicate that human serum accelerates the precipitation reaction and that this effect enhanced in the presence of EDTA. It is suggested that the effect of human serum may be due to C′1q of complement, found in the euglobulin fraction. These findings may explain some of the discrepancies obtained when serum luteinizing hormone and follicle-stimulating hormone are assayed utilizing double antibody radioimmunoassay methods with a sheep anti-rabbit gamma globulin precipitating system. Equalization of the human serum content of all samples and of the standards at the time of the precipitation reaction may minimize these discrepancies.

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