Cyclic expression of HLA class I and II molecules on the surface of purified human spermatozoa and their control by serum inhibin B levels

HLA class I and class II expression was analyzed weekly by cytofluorometry on spermatozoa samples from four donors during a 15-wk trial. On the same day that semen samples were studied, and to analyze whether this expression was hormone-controlled, serum levels of testosterone, LH, FSH, inhibin B, activin, and pro-alphaC on the one hand, and seminal plasma levels of inhibin B, activin, and alpha-inhibin on the other, were also measured. Inhibin B and related peptides were quantitated using a novel two-site assay with monoclonal antibodies to the alpha and beta subunits of inhibin. Our results showed that HLA class I and class II molecules were expressed on the spermatozoa's surface, following a cyclic pattern, and that there was a simultaneous and coordinated expression of both types of molecules (r = 0.801, P < 0.0001). Furthermore, when the expression of these molecules was plotted against the different hormone levels, serum inhibin B showed a clear inverse correlation with HLA class I (r = -0.612, P < 0.0001) and class II (r = -0.534, P < 0.0001). This finding reveals unexpected functions of inhibin B, which may be relevant in the fertilization process and on male fertility control.