PROTEIN-TYROSINE KINASE-ACTIVITY IN T-LYMPHOCYTES FROM PATIENTS WITH SYSTEMIC LUPUS-ERYTHEMATOSUS

We have recently observed an abnormal pattern of protein tyrosine phos phorylation in resting T lymphocytes obtained from peripheral blood of patients with systemic lupus erythematosus (SLE). To examine whether these findings may be related to dysregulated protein tyrosine kinase (PTK) function, we tested the relative amount and enzyme activity of t he main PTKs involved in the earliest signalling steps triggered via t he CD3 pathway. Cell lysates from peripheral blood T cells in SLE pati ents showed lower amounts of p59(fyn) and p56(lck) as shown by immunob lot. In contrast, the amount of ZAP-70, a PTK of the syk family, was c omparable in both groups. However, p59(fyn) immunoprecipitates obtaine d from unstimulated peripheral blood SLE T cells showed enhanced PTK a ctivity as compared to controls, whereas the PTK activity of p56(lck) and ZAP-70 molecules was comparable in both groups. The unchecked acti vity of the TCR/CD3-associated src kinase p59(fyn) may alter the balan ce needed for regulated T cell responses in SLE patients. (C) 1998 Aca demic Press