Reactivity of F(ab)2 fragments of sperm antibodies in agglutination, immobilization and immunofluorescence tests

Identification of human sperm antigens reacting with antisperm antibodies from sera and genital tract secretions

OBJECTIVE

To identify sperm antigens reacting with antisperm antibodies relevant in human infertility.

DESIGN

The reactions of separated sperm antigens with antibodies present in sera and genital tract secretions from infertile and fertile females and males were examined by immunoblotting techniques.

SETTING

The patients were followed in an outpatient setting of a hospital clinic.

PATIENTS

One hundred consecutive infertile males and females, referred for determinations of antisperm antibodies, comprised the study group. Fifty hospital and faculty employees with proven fertility served as a control group.

RESULTS

A high proportion of sera from fertile and infertile humans contained antibodies reacting with at least one sperm antigen. However, two discrete bands of antigenic proteins with molecular weights of 44 and 72 kd reacted significantly more frequently with serum antibodies from infertile females than from fertile females. No apparent correlation could be demonstrated between any particular antigen and serum antibodies from infertile males. Nevertheless, antigenic proteins of 62 kd were identified as the major sperm antigens reacting with antibodies present in seminal plasmas from infertile males.

CONCLUSIONS

The major sperm antigens reacting with systemic antibodies differ from the antigens recognized by local antisperm antibodies. Sperm antigens exhibiting relative molecular weights of 62 kd are major antigens reactive with local antisperm antibodies from infertile humans.

Auto- and iso-antigens of human spermatozoa detected by immunoblotting with human sera after SDS-PAGE

A sodium dodecylsulphate-polyacrylamide gel electrophoretic system for analysis of the proteins of human spermatozoa was established. Subsequent immunoblotting of the gels with human sera gave a reproducible immunolabelling of distinctive polypeptide bands. To identify auto- and isoantigens, 28 well-characterized sera from the WHO Reference Bank for Reproductive Immunology (1977, Acta Pathol. Microbiol. Scand. Sect. C, Suppl. 252) containing agglutinating and complement fixating antibodies (9 female (F) and 19 male (M) and 30 normal sera (14 F and 16 M) were analysed with reference to binding of IgG. Three spermatozoal antigens with Mr values in reduced state of 120,000 (6), 41,000 (6) and 32,000 (15) were found to be specifically correlated to the agglutinating activity of the reactive sea. (The number of these are given in parentheses). Furthermore, IgG from 2 and 3 of the normal sera and 14 and 17 of the agglutinating sera reacted with 78 and 64 kDA polypeptide, respectively. Identical binding patterns of IgG to spermatozoal polypeptides were obtained with IgG from male and female sera. The IgG-binding could not be correlated to the modes of spermatozoal agglutination. In a similar analysis of the IgM binding antigens of 21 agglutinating and 12 normal sera no differences in binding between the sera were found, except for a specific reaction to a 78 kDa antigen for 5 of the agglutinating sera.

Identification of antisperm antibodies on sperm of infertile men

An indirect radiolabeled antiglobulin test for plasma antisperm antibodies was modified so that sperm-associated antibodies could be identified. Ten of 16 (63%) infertile men with plasma IgG antisperm antibodies were found to have an elevated sperm-associated IgG. Two of these men with an elevated sperm-associated IgG also had an elevated sperm-associated IGA; one other man with plasma IgG antisperm antibodies, but no detectable sperm-associated IgG, was noted to have an elevated sperm-associated IgA. Eighteen infertile men with a history that suggested antibody-mediated infertility did not have plasma IgG antisperm antibodies; one (6%) of these men was found to have an elevated sperm-associated IgG; none of these 18 men were found to have an elevated sperm-associated IgA. No patient was found to have sperm-associated IgM.

The significance of the Fc part of antispermatozoal antibodies for the shaking phenomenon in the sperm-cervical mucus contact test

Donor spermatozoa with good motility were pretreated with four sera containing high titers of sperm-agglutinating IgG, one serum without sperm-agglutinating activity, the IgG fractions from these five sera, F(ab)2 and Fragment antigen binding (Fab) fragments from these sera and from the IgG fractions, and one seminal plasma sample with a high titer of sperm-agglutinating IgA. With mixed antiglobulin reaction tests the percentage of motile pretreated spermatozoa sensitized with IgG Fab or IgG Fragment crystalline (Fc) parts was determined. Spermatozoa sensitized with intact antispermatozoal IgG showed a strong reduction in their capacity to penetrate cervical mucus. The reduction of the penetration capacity was determined by estimation of the percentage of motile spermatozoa rapidly shaking (S%) in the sperm-cervical mucus contact (SCMC) test. Removal of the Fc parts resulted in a decreased S%. Treatment of spermatozoa, on which Fab fragments were present, with intact antibodies to IgG Fab fragments, resulted in a recurrence of a high S%. A decrease of the S% was also found if Fab fragments from antibodies to IgG Fc fragments were added to spermatozoa sensitized with intact antispermatozoal IgG. Similarly, it was found that a decrease of the S% occurred when IgA sensitized spermatozoa were treated with Fab fragments from antibodies to human IgA. In the sperm penetration meter test the IgA sensitized spermatozoa treated with Fab fragments from anti-human IgA antibodies showed a better penetration than untreated IgA-sensitized spermatozoa.