Active vitamin D3 reduces testicular tissue damage and inflammation in mice with autoimmune orchitis

Experimental autoimmune orchitis (EAO) is a well-established model of chronic epididymo-testicular inflammation associated with subfertility and infertility, and provides an in vivo tool to explore therapeutic agents for the treatment of testicular immunopathology. Here we aimed to investigate the effect of oral administration of 1,25-dihydroxyvitamin D3 (VD3) in mice with autoimmune orchitis. VD3, the biologically active vitamin D metabolite, has been linked to immunological processes by efficiently binding the intracellular vitamin D receptor (VDR) expressed in macrophages, dendritic cells, and T lymphocytes. VD3 was administered for 4 weeks to adult male C57BL/6J mice at the onset of orchitis induced by active immunization with testis antigens. Blood, testes, epididymis, and testicular draining lymph nodes (TLN) were collected at the end of treatment. VDR was expressed in testicular somatic and germ cells and in immune cells that infiltrate the interstitium of mice with orchitis. Histopathology provided evidence that the in vivo administration of VD3 led to a significant reduction in the incidence and severity of EAO. By analyzing the delayed-type hypersensitivity response to spermatic antigens, we showed that VD3 treatment reduced cell-mediated immunity. Concomitantly, CD11c+ cells from TLN of mice treated with VD3 presented, compared to the vehicle group, a significantly higher expression of PD-L1, essential for peripheral tolerance. Serum levels of IL10 increased in mice treated with VD3. The effect of VD3 on EAO followed the same anti-inflammatory pattern shown for other models of autoimmune inflammation, validating its therapeutic use for the treatment of male reproductive pathologies associated with epididymo-testicular inflammation.