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

Summary 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 macropliotography 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 tinal response ranging from sparse regrowth to a near normal coal. 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.