DIFFERENTIAL REQUIREMENT FOR PROTEIN-TYROSINE KINASE FYN IN THE FUNCTIONAL ACTIVATION OF ANTIGEN-SPECIFIC T-LYMPHOCYTE CLONES THROUGH THE TCR OR THY-1

The protein tyrosine kinase Fyn has been shown to be involved in signa l transduction through the TCR and the glycosyl-phosphatidylinositol-l inked surface molecule Thy-1 expressed on T cells. In this study, we e xamine the requirement for Fyn expression in signaling through the TCR or Thy-1 using a panel of Ag-specific T cell clones derived from fyn( -/-) mutant mice. These clones do not express normal Fyn protein, as m easured by immune-complex kinase reaction using anti-Fyn Ab. Stimulati on through the TCR, either by APC bearing relevant Ag or by immobilize d anti-CD3 mAb, resulted in comparable levels of proliferation, lympho kine production, and cytolysis by clones from both wild-type and fyn(- /-) mice. In contrast, stimulation through Thy-1, using soluble (or cr oss-linked) anti-Thy-1 mAb, was deficient, as measured by these respon ses. Thus, Fyn expression is selectively required for functional activ ation through Thy-1 in these T cell clones.