Involvement of CD44 in leukocyte recruitment to the rat testis in experimental autoimmune orchitis

Experimental autoimmune orchitis (EAO) is characterized by an interstitial mononuclear cell infiltrate and a severe lesion of the seminiferous tubules with germ cells that undergo apoptosis and sloughing. The aim of this study was to determine the role of CD44 in testicular leukocyte recruitment in EAO. The biological functions of CD44 have been attributed to the generation of a functionally active hyaluronan-binding phenotype. Orchitis was induced in Sprague-Dawley adult rats by active immunization with an emulsion of testicular homogenate and complete Freund's adjuvant using Bordetella pertussis as co-adjuvant. Control rats (C) injected with saline and adjuvants and normal (N) untreated rats were also studied. CD44 expression was analyzed by flow cytometry in peripheral blood mononuclear cells (PBMC) and lymph node cells isolated from rats at different times after the first immunization. We observed an increase in the mean fluorescence intensity of both samples in the C and experimental (E) groups only after the immunization period. A significant decrease in percentage of CD44+PBMC and in mean fluorescence intensity was observed in rats with orchitis compared with the C group. By in vitro hyaluronic acid-binding assay we demonstrated that the percentage of PBMC adhesion was higher in the E group compared with the C and N groups. By immunohistochemistry, we observed a significant increase in the number of CD44+cells in the testicular interstitium of rats with severe orchitis compared with the N and C groups. These results suggested that the CD44 molecule is involved in the homing of lymphomonocytes into the testes of rats with autoimmune orchitis.