Differential production of interleukin-3 in human T lymphocytes following either CD3 or CD2 receptor activation.

Interleukin-3 (IL-3) is expressed in T lymphocytes and stimulates the growth of multipotent hematopoietic progenitors. Little is known, however, about the stimuli that lead to IL-3 protein release. We examined IL-3 and granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNA expression and protein secretion in human T lymphocytes following activation via the TCR/CD3 complex, the CD2 receptor, and the IL-2 receptor. GM-CSF mRNA expression and protein release were found in CD3 and CD2 activated T cells with maximum GM-CSF release following stimulation with IL-2. IL-3 protein release is regulated via the CD2 receptor with virtually no IL-3 release after T cell stimulation via CD3. In contrast, IL-3 mRNA accumulation is more pronounced after CD3 activation than after CD2 activation. This suggests that upregulation of IL-3 protein release following T cell stimulation via CD-2 occurs largely at the translational or posttranslational level. These data also indicate that differential control of cytokine production can occur in response to activation of the alternative T cell receptor. Interaction of the T cell CD2-receptor with its natural ligand LFA-3 expressed on stromal cells might represent a regulatory mechanism for rapid release of IL-3, facilitating proliferation of multipotent hematopoietic cells.