Phagocytosis of human post-capacitated spermatozoa by macrophages

BACKGROUND: Earlier studies demonstrated that macrophages phagocytize spermatozoa in the female genital tract of mammals. In spite of this phagocytosis, fecundity is not affected, raising questions of how the resulting decrease in the number of spermatozoa does not reduce the fertilization rate and of the role of this phagocytosis. We hypothesized that its role is to rid the female genital tract of spermatozoa past their fertilizing stage (post-capacitated spermatozoa). Here we examined whether, indeed, phagocytosis is restricted to post-capacitated spermatozoa. METHODS: Spermatozoa were incubated for 22 h either in a medium that allows them to become capacitated and then post-capacitated, or in a medium that prevents them from acquiring these states. These sperm populations were compared for their susceptibilities to macrophage phagocytosis. RESULTS: Phagocytosis was significantly higher (P << 0.001) in the sperm population containing post-capacitated spermatozoa. Vitality, motility, the acrosomal status and the proportion of capacitated cells did not affect phagocytosis. CONCLUSION: Post-capacitated spermatozoa are, probably, preferentially phagocytized by macrophages.