The significance of several local factors in prolonging allograft survival in the rat testis has been investigated. The lower temperature of this organ was shown to have no effect, because parathyroid gland allografts implanted s.c. in the ear, which is similarly hypothermic, were rejected as promptly as in conventional sites. Conversely, testes secured in the abdominal cavity afforded privilege to grafts just as well as normal testes. With indirect immunofluorescence using a monoclonal antibody, it was shown that the testis’ interstitial tissue is well-endowed with cells bearing class II histocompatibility antigens, a prerequisite for antigen-processing capability. When intratesticular allograft recipients were pretreated with estrogen to suppress Leydig cell synthesis of testosterone, most grafts were rejected promptly, suggesting that local steroid secretion is important in testicular immune privilege. Both testes and s.c. sites supported inflammatory reactions to cotton pledgets, indicating that there is no interference with the nonspecific inflammatory process necessary for graft rejection, but more likely with antigen processing itself.
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