Abstract: In order to determine the biological role of antisperm IgA,especially secretory IgA,in immunological infertility and in the development of an antisperm contraceptive vaccine,a panel of monoclonal IgA (moIgA) antibodies to lactate dehydrogenase C4 (LDH-C4) were prepared by intraintestinal immunization,and their heterogeneous isoforms were demonstrated by Western blotting.Most moIgAs (PA1-PA5) were obtained by the combined use of intraintestinal immunization and fusion of Peyers patch cells for parent cells.In the presence of guinea pig serum complement,mouse sperm were immobilized by moIgA PA1,PA2 and PA4.Mouse sperm were agglutinated by PA4 and PA5 at high concentration.The rates of in vitro fertilization were significantly reduced by 3 of 7 moIgA tested,but moIgA (PA1,PA2 and PA5) had no significant effects on mouse in vivo fertilization by passive immunization.Purified murine bile secretory component was assembled with either purified moIgA or moIgA in ascites in vitro.The effects of moIgA on sperm immobilization,sperm agglutination and in vitro fertilization were not significantly changed following the binding of the moIgA with secretory component.These results provide direct evidence of a positive biological role of anti-LDH-C4 moIgA and secretory IgA in sperm function and in vitro fertilization.