Aim: The expression of the cytokines IL-2, IL-6, IL-10, IFN-g and TNF-a and the adhesion proteins CD99 and CD106 was studied in the human testis at the protein level.
Methods: The expression of the cytokines and the adhesion proteins was assessed using immunohistochemistry and immunoblotting.
Results: None of the cytokines studied was present in the human testis, but CD99 and CD106 (VCAM-1) strongly were expressed in all the testes investigated. CD99 was present in the interstitial tissue of the human testis as well as in the Sertoli cells. The identity of the CD99+ interstitial cells is unclear. CD106 (VCAM-1) was present in Leydig cells as well as the basal parts of the Sertoli cells in the seminiferous tubules. In immunoblotting, CD99 was demonstrated at molecular ratios of 46-57 (kD). This is a novel isoform of the molecule.
Conclusion: The human testis produces both CD99 and CD106 and as CD106 mediates cell binding to lymphocytes, it is possible that the human Leydig cells adhere to lymphocytes like the rodent Leydig cells.