In vivo depletion of CD8+ T cells restores hair growth in the DEBR model for alopecia areata.

Alopecia areata (AA) is a putative autoimmune disease in which anagen hair follicles are the target of immune cell attack. While both CD4+ and CD8+ T lymphocytes are prominent in the infiltrate, their respective roles in the pathogenesis of AA remain unknown. Here we directly investigated the activity of CD8+ cells in the inhibition of hair growth using the Dundee experimental bald rat (DEBR) model for AA. Eight lesional DEBRs were fully depleted of their CD8+ cells by intraperitoneal injection of OX-8 monoclonal antibody (MoAb) specific for these cells over a 15-day therapy course. A control group of eight lesional rats was injected with the irrelevant MoAb OX-21. Sequential blood samples were analysed by flow cytometry to observe changes in the CD8+ cell population and macrophotography used to record changes in hair growth activity. All eight CD8+ depleted rats started to regrow hair within 29 days from the start of treatment, the final response ranging from sparse regrowth to a near normal coat. While two rats maintained their new pelage, the remainder lost hair as the CD8+ population in peripheral blood increased. Two of the control rats also showed hair regrowth over the experimental period of 156 days. These results suggest that CD8+ cells play an active part in the pathogenesis of AA. As hair production did not fully recover in all animals, immune mechanisms other than CD8+ cells may be involved in effecting hair loss. However, analysis of CD8+ cell levels in the skin of CD8+ depleted rats may help resolve their full importance in AA.