Immunological responses of patients with psoriasis and the effect of treatment with methotrexate.

A group of thirty-six patients of whom fourteen were being treated with methotrexate, were studied in order to assess T-lymphocyte function by in vitro techniques. Circulating T-lymphocytes in aliqots of blood were assessed by the rosetting technique. No differences were found in psoriatics, whether on methotrexate or not, compared with fifteen control subjects. Lymphocyte counts and lymphocyte transformation to phytohaemagglutinin (PHA) tended to be lower in the psoriatic group as a whole than in the controls, but the differences were not statistically significant, However, a significant inverse relationship was found between the extent of the skin lesions and lymphocyte transformation to PHA, i.e. the smaller the area of skin affected the higher the lymphocyte transformation. Psoriatics treated with methotrexate had fewer skin lesions and higher lymphocyte transformation to PHA than psoriatics not so treated, probably reflecting this inverse relationship. The reason why the presence of extensive psoriasis is associated with depressed lymphocyte transformation is not understood. No evidence was found that methotrexate depressed cell-mediated immunity as judged by these in vitro tests.