Analysis of HLA class Ib gene expression in male gametogenic cells

We have investigated mRNA expression for nonclassical MHC class I genes (HLA-E,-F,-G) in human gametogenic cells. Testicular tissue was treated by collagenase and the resulting cell suspension was further purified by fractionation on Percoll gradients in a two-step procedure. Three gametogenic cell fractions were analyzed: purified heterogenous suspension of gametogenic cells, fraction of round spermatids and fraction of elongated spermatids. Total RNA isolated from each cell population was subjected to both reverse transcriptase/polymerase chain reaction and Northern blot analysis using oligonucleotides specific for HLA-E, -F and -G. Both method gave similar results. We have found a considerable level of HLA-E mRNA, very low amounts of reamplified cDNA for HLA-F and both a complete lack of mRNA and reamplified cDNA for the HLA-G gene in the analyzed gametogenic cell fractions. Additionally, we have localized HLA-E molecules on the cells of the adluminal compartment within seminiferous tubules using immunostaining with monoclonal antibodies specific for HLA-E heavy chain followed by confocal microscopy analysis. The unique expression pattern of HLA class I antigens in the male gonad could play an important role in an efficient protection against an autoimmunological attack toward germ cells.