Antibodies directed against sperm membrane
antigens located mainly over the sperm heads were eluted from the sperm cell fraction of autoimmune ejaculates and transferred to antibody-negative spermatozoa of fertile donors. The ability of these antibody-coated spermatozoa to bind to the human zona pellucida and to penetrate
zona-free hamster oocytes was evaluated in vitro. The majority of the sperm-eluted samples contained both
IgA and
IgG antibodies. In order to evaluate the effect of each class of antibody on the analyzed sperm functions, each isotype was 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 consistently reduced by 60-85% by the five eluted samples tested. Removal of either
IgA or
IgG antibodies from the eluted samples did not change 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 sperm penetration. Three of them decreased the penetration by 67-78%, while 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 isotypes restored the ability of the sperm to penetrate the hamster oocytes. These results suggest that sperm-associated
antibodies may have different effects on
zona-binding and gametic fusion events that lead to fertilization. Whereas
IgA and
IgG antibodies taken together or separately decreased sperm binding to the human zona pellucida, the two classes of
antibodies must be associated in order to impair sperm penetration into
zona-free hamster oocytes.