Factor requirements for activation and proliferation steps of human CD2+CD3-CD4-CD8- early thymocytes.

Human CD2+CD3-CD4-CD8- thymocytes were shown to display high in vitro growth ability although their factor requirements for activation and proliferation are not fully known. We have thus isolated these precursors and assayed their activation and proliferation potentials in response to various factors. Our results indicate that these cells proliferate in response to phytohemagglutinin (PHA), recombinant interleukin 2 (rIL 2) and rIL 4. Simultaneous addition of anti-CD2I + III monoclonal antibodies (mAb) and rIL 2 highly increased cell growth while IL 4-induced proliferation was not enhanced upon addition of anti-CD2. Anti-CD2 and PHA, but not IL 2, induced intracytoplasmic Ca2+ influx phosphatidyl inositol turnover as well as IL 2 receptor expression. Sequential studies indicated that CD2 triggering enable many more CD2+ precursors to respond to rIL 2. Endogenous IL 2 synthesis was necessary for PHA-induced cell growth. Neither of these in vitro treatment were able to induce membrane expression of CD3, CD4 or CD8 on CD2+ cells.