EXPRESSION OF FUNCTIONAL TRK TYROSINE KINASE RECEPTORS AFTER T-CELL ACTIVATION

Increasing evidence indicates that nerve growth factor (NGF), in addit ion to its neurotrophic actions, exerts specific effects on cells of t he immune system. This report shows that the CD4-positive T cell line 9/6 expresses trk protooncogene, the signal transducing receptor unit for NGF, after TCR-mediated activation by Ag and APC. This receptor is of functional importance because interaction of NGF with Ag-stimulate d 9/6 T cells induced the transcriptional activation of the c-fos gene , a hallmark of the biochemical response to NGF. Our findings that nei ther mitogen nor Ag stimulation induced the expression of the low affi nity NGF receptor in 9/6 T cells indicate that trk alone is sufficient to mediate biologic activity of NGF in T lymphocytes.