A major mRNA of the human epididymal principal cells, HE5, encodes the leucocyte differentiation CDw52 antigen peptide backbone.

HE5, a very abundant human epididymal gene product, was cloned by a differential screening procedure which employed testis as the primary negative control tissue. Sequencing of the HE5 cDNA showed it to be identical to that encoding the peptide backbone of the human leucocyte differentiation antigen CDw52. Since human genomic DNA contained only one cross-hybridizing fragment, this implies that both products were transcribed from the same gene. Northern blot analysis and in situ transcript hybridization revealed a highly tissue- and cell-type-specific expression pattern for HE5, showing the gene product to originate from epithelial cells of the epididymal and deferent duct. The possible identity of the HE5 product with the CDw52 antigen suggests a link between the immune and reproductive systems.