| Research Abstract |
1. Antibodies induced to appear in the blood of Nile tilapia, oreochromis niloticus, by i. p. injections of tilapia spermatozoa as an antigen were shown to be highly specific to tilapia spermatozoa, and were capable of recognizing 15 kinds of proteins as surface antigens localizing on the sperm plasma membrane. Among these proteins, 6 kinds were identified as autoantigens. The sperm-specific antigens made their first appearance on spermatids at the late spermiogenetic stage, concomitantly with the establishment of the blood testis barrier in tilapia testis.
2. By partial removal of the testis of mature males in vivo, cellular and humoral autoimmune responses could be successfully induced in the fish resulting from the diffusion of germ cell elements into the body cavity. Simultaneous treatment of the fish with Freund's complete adjuvant (FCA) could augment the cellular, but not the humoral, responses, through patliological responses were seen to be restricted to the sperm duct system of
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treated fish.
3. As a preliminary test to yield the anti-sperm antibody in a large scale, tilapia antibody raised against bovine serum albumin (BSA) was isolated and partially characterized. The antibody was highly specific to BSA, and had solely the nature of tilapia IgM. Antisera obtained from male tilapia injected with BSA + FCA produced strong precipitin lines in a wide range of antigen concentrations in an immunoabsorption assay, in which IgM was demonstrated to be exclusively implicated. Antigen binding capacity of the antibody was shown to be considerably high.
4. Male tilapia, immunized with testis material showed a prominent regression in their fertilizing ability, which was accompanied by agglutination and reduced motility of their spermatozoa, 4 to 8 weeks after initial immunization. Anti-tilapia sperm autoantibodies were isolated and purified from sera of the treated fish, added to the newly developed artificial seminal plasma for Nile tilapia, and used for coating spermatozoa by incubating them in this plasma for a given duration of time. The resultant spermatozoa, which were presumed to have been coated by the anti-sperm autoantibodies, showed a considerable diminution in their fertilizing capacity. It was thus concluded that the anti-sperm autoantibodies, which were induced to appear in male tilapia by immunization with testis material, invade the testicular lumina following destruction of the blood-testis barrier, come to be bound to the sperm surface antigens that are functionally implicated in fertilization, and thus impede a fertilizing capacity of the spermatozoa. Furthermore, the antibodies seem to affect to sperm agglutination and Sertoli cell pliagocytosis which appear to be additional factors leading to partial sperm infertility. Less
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