Study of antisperm antibodies bound to the sperm cell surface and their relationship to circulating ASA

Direct and indirect tests for antisperm antibody (ASA) detection are commonly used in laboratories for the diagnosis of male immunological infertility. Even though the two kinds of tests study the same immunological phenomena, frequently no perfect correlation is found even on large series of patients and with precise statistical models. The aim of the present investigation was to try to establish whether biological models can explain the antibody test results and if a predictive threshold can be established for expected positivity/negativity.

The data relate to 667 patients, who were screened using the Direct Immunobead test (d-IBT) for ASA bound to the sperm surface and with the gelatin and tray agglutination test (GAT and TAT) in sera for circulating ASA. Correlation were studied and cases of no correlation were further analyzed.

The number of patients with a clinically significant positivity to d-IBT (binding percentage > or = 20%) was 134 (20.1% of total patients). The analysis of the results of direct and indirect tests shows that the discordances are due to differences in the Ig class of immunization or to the site of epitopes involved. In fact, as far the Ig class is concerned, if d-IBT shows a prevalent or exclusive IgG or IgA positivity, this results in a poor correlation between binding percentage to d-IBT and GAT-TAT titers. If both the Ig classes are involved, the level of positivity of the two kinds of test are strictly related. As far as the site of Ag-Ab reaction on the sperm surface is concerned, the wide immunization involving all the surface sperm antigens (mixed), shown by d-IBT, is related to higher indirect test titers.

Local and systemic antisperm immunizations are strictly related and a predictive threshold of expectation can be established to explain even apparently discordant direct and indirect results.