Transient CD44 variant isoform expression and reduction in CD4+/CD25+ regulatory T cells in C3H/HeJ mice with alopecia areata

Alopecia areata, an autoimmune disease affecting anagen stage hair follicles, can be induced by grafting spontaneous alopecia areata affected skin to normal-haired C3H/HeJ mice. As the onset of alopecia areata can be significantly retarded by anti-CD44 variant isoform 10 treatment, it was interesting to explore the underlying disease mechanism. Two weeks after transplanting alopecia areata affected skin, expression of CD44 variant isoforms 3, 6, 7, and 10 was strikingly upregulated as compared with sham-grafted mice. By 6 wk after grafting, CD44 variant isoform levels had returned to normal, whereas in draining lymph nodes, CD44 variant isoform expression was slightly decreased. Leukocytes in the skin of mice with chronic alopecia areata expressed a hematopoietic isoform of CD44 and CD44 variant isoform 6 at an elevated level, but CD44 variant isoform 3 expression was reduced. Cytokine expression in leukocytes of chronic alopecia areata affected skin was higher than in normal-haired controls. Cytokine expression also increased postsurgery in sham and alopecia areata grafted mice, but remained elevated only in mice receiving alopecia areata affected skin. Finally, from the skin of mice with chronic alopecia areata and of mice transplanted with alopecia areata affected skin, an increased number of CD4(+) and CD8(+) cells, but a strongly decreased number of CD4(+)/CD25(+) regulatory T cells was recovered. Thus, expression of CD44 variant isoforms is important for the migration of leukocytes during the initial period of alopecia areata. CD44, however, is apparently not involved in the maintenance of the disease state, which is characterized by high cytokine expression levels, an increased number of CD4(+) and CD8(+) cells, but a low level of CD4(+)/CD25(+) suppressor cells.