Human prostasomes express CD48 and interfere with NK cell function.

Prostasomes are small vesicles secreted by the prostate gland to the seminal fluid. In male fertility, the fusion of prostasomes to sperm has been associated with an enhancement of sperm function. Prostasomes also contribute to sperm protection within the female reproductive tract and immunologically relevant proteins have been identified on the prostasomal membrane that may prevent immune-mediated destruction of the sperm.The female genital tract is a potentially hostile environment for spermatozoa and a large number of NK cells have been found in the female reproductive tract. Since it has been suggested that NK cells may represent an important component of innate immunity in the female reproductive tract, we have analyzed the role of prostasomes in the regulation of NK cell activity.Flow cytometric analysis revealed that prostasomes expressed high levels of CD48, the ligand for the activating receptor CD244. The interactions between NK cells and purified prostasomes resulted in a decrease of CD244 expression. Moreover, the decreased NK cell activity observed in NK cells cultured in the presence of prostasomes suggests that prostasomes may immunomodulate the local environment within the female reproductive tract preventing immune-mediated sperm destruction and prolonging their survival rate.