Lack of HLA-molecules on human spermatozoa and in seminal plasma

The expression of human leukocyte antigens (HLA) on ejaculated spermatozoa and on lymphocytes was compared by flow cytometry using monoclonal antibodies towards HLA class I (pan-HLA-A, -B, -C) and class II (DR) antigens. Soluble antigens of HLA class I (s HLA-A, -B, -C) in seminal plasma and in blood plasma were monitored with an ELISA technique. Lymphocytes showed specific fluorescence after incubation with the antibodies against HLA class I and class II (DR), whereas, on spermatozoa no positive immunofluorescence could be detected. No antibodies were bound to any significant extent either after modifications of sperm preparation (density gradient centrifugation, swim up-technique, addition of azide, foetal calf serum or benzamidine chloride) or after treatment of spermatozoa with detergents. Furthermore, different concentrations of soluble HLA-A, -B, -C in seminal plasma and in blood plasma were detected. The latter one showed soluble HLA about four-fold more concentrated than the seminal plasma (means +/- SD: 262.5 +/- 144.4 nmol l-1 vs. 62.5 +/- 27.1 nmol l-1). These results suggest, that the HLA-expression differs between human spermatozoa and somatic cells.