Immune responses to spermatozoa in homosexual men

Immunologic responses to spermatozoa were investigated in homosexual and heterosexual men. Ten of 18 (56%) of the homosexual men had serum levels of IgG antibody to spermatozoa that were at least 2 standard deviations above the mean level for the heterosexual men; only 2 homosexual men had IgA antibody to spermatozoa. Similar increases above heterosexual levels in sperm-related antigen were detected in the sera of 56% (10 of 18) of the homosexual men. Circulating immune complexes (CICs) were detected at high levels (greater than 1000 micrograms/ml) in 61% (11 of 18) of the homosexual men. The CICs were relatively small (less than 14S), as determined by sucrose gradient analysis. Only 3 of 18 (17%) of the heterosexual men had CICs, and these were at a much lower concentration (less than or equal to 700 micrograms/ml). In the homosexual men, CICs and sperm-related antigen levels were positively correlated (r = 0.41, P less than 0.001), while IgG sperm antibody levels were negatively correlated with both CIC levels (r = -0.24, P less than 0.01) and sperm-related antigen levels (r = -0.24, P less than 0.01). CICs from six homosexual men were analyzed for composition. All contained IgG, and two had evidence of sperm-related antigen. The results suggest that intake of spermatozoa via the alimentary canal may lead to the development of a humoral immune response to spermatozoa.