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 asso ciated with infections by group A beta-haemolytic streptococci. In a previo us study of patients with active psoriasis we demonstrated an increased fre quency of circulating Th1-like cells that responded to 20 amino acid (aa) s treptococcal M-peptides sharing sequences with human keratin. These cells d isappeared after ultraviolet B (UVB)-induced clinical remission. Using T ce lls from the blood of 17 psoriatic patients and 17 healthy controls we have now compared the numbers of interferon-gamma (IFN-gamma)-producing cells i nduced 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 th is peptide were stronger than to the corresponding M-peptide containing the ALEEAN sequence. After UVB treatment T cell responses to all the M- and ke ratin peptides were abolished, while responses to the positive control anti gen streptokinase/streptodornase (SK/SD) were not affected. These findings are consistent with the notion that aa sequences which keratin has in commo n with M-protein may be a major target for autoreactive T cells in psoriasi s.