81-P: POLYMORPHIC FREE HLA CLASS I HEAVY CHAINS ARE EXPRESSED BY MALE GAMETOGENIC CELLS IN THE HUMAN TESTIS

Aim The expression of major histocompatibility complex (MHC, in humans HLA) antigens is widely regarded as a property of all nucleated cells. These molecules are expressed very strongly by cells of lymphatic tissues, while many cells in other tissues, (e.g. muscle cells, neurons) express only small amounts of these antigens. The functional consequences of this differential expression and the molecular control mechanisms are not well understood. Immunologically privileged tissues (e.g. brain, seminiferous tubules within the testis) are separated from circulating immune effector cells by blood–tissue barriers. These barriers can be surmounted only under pathological conditions. Therefore, since cells that bear the classical interaction partners of MHC-I such as T cell receptors are usually lacking, it would appear that MHC-I expression by cells within immunologically privileged sites serves no immunologically meaningful function. The purpose of the present study was to investigate the expression of structurally distinct forms of HLA class I molecules in testicular tissue. Methods Immunohistochemistry, Confocal laser scanning microscopy, Western blotting, in situ hybridization. Results Immunohistological analyses using monoclonal antibodies (mAb) revealed reactivity within seminiferous tubules of the testis exclusively with mAb directed against free HLA class I heavy chains (HC), while reagents against β 2-m and HC/ β 2-m complexes stained only cells in the interstitium. The former mAb reacted with sperm precursor cells, mainly preleptotene spermatocytes and pachytene spermatocytes I, but not spermatogonia or more mature germ cells including spermatozoa. Sertoli cells were also found to be unreactive. Locus-specific mAb such as HC10 or LA45 indicate tubular expression of highly polymorphic HC. Conclusions Our results suggest a function for polymorphic HLA class I HC, possibly in the context of an interaction with sperm-expressed guidance receptors within immunologically privileged sites of the testis.