DEFICIENT EXPRESSION OF P56(LCK) IN TH2 CELLS LEADS TO PARTIAL TCR SIGNALING AND A DYSREGULATION IN LYMPHOKINE MESSENGER-RNA LEVELS

Activation of T lymphocytes through their TCR is regulated by a delica te balance of phosphorylation and dephosphorylation of protein substra tes by protein tyrosine kinases (PTKs) and phosphotyrosyl phosphatases , respectively, One of the earliest steps in the activation pathway is thought to involve the Src family PTKs, p56(lck) (Lck) and p59(fyn) ( Fyn); however, the precise contribution of each PTK in TCR-mediated si gnaling remains incompletely understood, To study the role of Lck in m ature T cells, antisense RNA was used to inhibit its expression in a n ontransformed Th2 clone. In this report, we demonstrate that specific inhibition of Lck expression in Th2 cells, in the presence of normal l evels of functional Fyn PTK, has profound consequences on multiple eve nts following TCR stimulation, including an altered pattern of tyrosin e-phosphorylated substrates, defective phosphorylation of TCR-zeta and ZAP-70, defective Ca2+ mobilization, and a similar to 90% reduction i n proliferative responses to antigenic and mitogenic stimuli. In contr ast, Lck-deficient cells expressed constitutively elevated levels of l ymphokine mRNA, including IL-4, IL-5, and IL-10, and were capable of s ecreting IL-4 upon activation through the TCR. These results demonstra te a dissociation in functional responses in Lck-deficient Th2 cells a nd suggest a role for Lck in the induction of a state of T cell unresp onsiveness.