Cross-Reactivity of Human Luteinizing Hormone (β- Subunit) and a Serine Protease Demonstrated by Immunoperoxidase Staining in Human Oocytes*

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Abstract
Localization of the β-subunit of human LH (hLHβ) in the cytoplasm and nucleus of human oocytes obtained from antral follicles at different times of the menstrual cycle was demonstrated by immunohistochemical techniques. The presence of considerable amounts of LH at cycle times other than during the surge coupled with two puzzling technical aspects of the localization prompted further study based on a cross-reactivity with serine proteases suggested by other reports. Complete elimination of the staining reaction was achieved by prior absorption of the hLHβ antiserum with hLHβ, the synthetic homologous (CAGY) sequence [H2N-Thr- Gly-Tyr-His-NH2].Almost total elimination was observed after absorption with normal human plasma, while partial blocking was achieved after absorption with chymotrypsinogen A. Staining of sections of rat and human anterior pituitary glands was used to evaluate the completeness of the absorption of antihLHβ with hLHβ. No appreciable difference was seen in the staining of the gonadotrophs by anti-hLHβ before or after the absorption with CAGY or chymotrypsinogen plus Trasylol, but the reaction was completely eliminated by the absorption with hLHβ. The most likely explanation for these findings lies in the probability that anti-hLHβ contains antibodies to the CAGY sequence which were recognizing similar sequences in serine proteases in the human oocytes.