Is an epitope on keratin 17 a major target for autoreactive T lymphocytes in psoriasis?
Psoriasis is a T cell‐mediated inflammatory skin disease that has been associated with infections by group A β‐haemolytic streptococci. In a previous study of patients with active psoriasis we demonstrated an increased frequency of circulating Th1‐like cells that responded to 20 amino acid (aa) streptococcal M‐peptides sharing sequences with human keratin. These cells disappeared after ultraviolet B (UVB)‐induced clinical remission. Using T cells from the blood of 17 psoriatic patients and 17 healthy controls we have now compared the numbers of interferon‐gamma (IFN‐γ)‐producing cells induced by seven 18–20 aa keratin peptides and five corresponding M‐peptides. The most frequent and strongest responses were observed to a peptide from keratin 17 that shares ALEEAN sequence with M‐protein. The responses to this peptide were stronger than to the corresponding M‐peptide containing the ALEEAN sequence. After UVB treatment T cell responses to all the M‐ and keratin peptides were abolished, while responses to the positive control antigen streptokinase/streptodornase (SK/SD) were not affected. These findings are consistent with the notion that aa sequences which keratin has in common with M‐protein may be a major target for autoreactive T cells in psoriasis.