EFFECT OF SPERM-ASSOCIATED ANTIBODIES ON HUMAN SPERM ABILITY TO BIND TO ZONA-PELLUCIDA AND TO PENETRATE ZONA-FREE HAMSTER OOCYTES

Antibodies directed against sperm membrane antigens located mainly ove r the sperm heads were eluted from the sperm cell fraction of autoimmu ne ejaculates and transferred to antibody-negative spermatozoa of fert ile donors. The ability of these antibody-coated spermatozoa to bind t o the human zona pellucida and to penetrate zona-free hamster oocytes was evaluated in vitro. The majority of the sperm-eluted samples conta ined both IgA and IgG antibodies. In order to evaluate the effect of e ach class of antibody on the analyzed sperm functions, each isotype wa s specifically absorbed before transfer. Sperm-binding to salt-stored zona pellucida, as assayed by FITC and TRITC labeling of antibody-free and antibody-coated spermatozoa incubated with the same zona, was con sistently reduced by 60-85% by the five eluted samples tested. Removal of either IgA or IgG antibodies from the eluted samples did not chang e the overall effect. Sperm penetration of zona-free hamster eggs was variously affected by sperm-associated antibodies. Of the 8 samples of sperm-eluted antibodies tested, only 4 had a significant effect on sp erm penetration. Three of them decreased the penetration by 67-78%, wh ile the fourth exhibited a modest increasing effect of 39%. These four samples contained antibodies of the two isotypes. In the samples with a decreasing effect, the elimination of one or another of the two iso types restored the ability of the sperm to penetrate the hamster oocyt es. These results suggest that sperm-associated antibodies may have di fferent effects on zona-binding and gametic fusion events that lead to fertilization. Whereas IgA and IgG antibodies taken together or separ ately decreased sperm binding to the human zona pellucida, the two cla sses of antibodies must be associated in order to impair sperm penetra tion into zona-free hamster oocytes.