MOLECULAR-WEIGHTS AND ISOELECTRIC POINTS OF SPERM ANTIGENS RELEVANT TO AUTOIMMUNE INFERTILITY IN MEN

Purpose: We determined the molecular weights and isoelectric points of antigens in the uncapacitated and capacitated spermatozoa of fertile men binding to the serum immunoglobulin G (IgG) from 8 autoimmune infe rtile men and 8 fertile nonautoimmune men. Materials and Methods: We u sed double fluorochrome cytotoxicity and immunobead binding assays to determine the sperm antibody status of the study subjects. 2-Dimension al gel electrophoresis and Western blot analysis were used to determin e the molecular weights and isoelectric points of sperm antigens bindi ng to-serum IgG from these men. Amino acid sequencing of the digested peptides of chosen proteins was accomplished. Immune reactivity to the proteins in autoimmune infertile men was further verified. Results: S erum IgG from fertile men failed to react significantly. Serum IgG fro m all autoimmune men (100%) showed significant binding to proteins wit h a molecular weight of 92 kDa. and isoelectric points of 3.5 to 4.0 i n the capacitated spermatozoa. Six of 8 infertile men (75%) had serum IgG binding to capacitated sperm antigens with a molecular weight of 1 8 kDa. and isoelectric points of 4.5 to 5.2. Amino acid sequencing of peptides of the 92 kDa. protein matched complement component 1 (C1) in hibitor, with noted differences in the amino acid sequencing from the latter. The 18 kDa. protein matched calmodulin. We verified that serum IgG from autoimmune infertile men bound with C1 inhibitor and ascerta ined that the 92 kDa. protein in the spermatozoa was C1 inhibitor-like protein. Conclusions: Significant antibody responses to C1 inhibitor- like protein and calmodulin were noted in autoimmune men. Both of thes e proteins may be of testicular origin and these autoimmune responses may be highly relevant to infertility.