DIPLOID EXPRESSION OF HUMAN-LEUKOCYTE ANTIGEN CLASS-I AND CLASS-II MOLECULES ON SPERMATOZOA AND THEIR CYCLIC INVERSE CORRELATION WITH INHIBIN CONCENTRATION

A diploid expression of class I and class II human leukocyte antigens (HLA) has been found in purified spermatozoa by using double fluoresce nce labeling cytofluorometry and relevant monoclonal antibodies; this expression has been confirmed for the first time by the analysis of sp ecific HLA mRNA and metabolic S-35 labeling followed by immunoprecipit ation, which demonstrates an active ongoing translation of HLA protein s in germinal cells. Long-living mRNA coming from diploid germinal cel ls may be translated to HLA molecules in spermatozoa. This translation is controlled (or at least inversely correlated) by a testicular horm one (inhibin) in a cyclic fashion. Remarkably, serum levels of inhibin , synthesized by Leydig and Sertoli cells, follow a 12- to 13-day cycl e, with a peak level at Day 6; this is probably controlled by FSH (not cyclic in males) and other testicular and/or unknown hormones. Peak l evels of inhibin concur with the lower density and percentage of sperm atozoa expressing both HLA class I and II molecules (close to 3% by cy tofluorometry); lowest levels of inhibin coincide with the highest num bers (35-40%) of spermatozoa positive for both HLA molecules and a hig her surface density. These observations could put to an end a disconce rting and long-lasting controversy on the expression/non-expression of HLA antigens on spermatozoa. The possibility that HLA-bearing spermat ozoa are more capacitated for fertilization than those that do not bea r HLA, and the implications of our results on male fertility control a re also discussed.