DEVELOPMENT IN-VITRO OF HUMAN CD4(- EXOGENOUS INTERLEUKIN-12 IS REQUIRED FOR PRIMING THYMOCYTES TO PRODUCE BOTH TH1 CYTOKINES AND INTERLEUKIN-10() THYMOCYTES INTO FUNCTIONALLY MATURE TH2 CELLS )

Fresh postnatal thymocyte cell suspensions were directly cloned under limiting dilution conditions with either phytohemagglutinin or toxic s hock syndrome toxin-1 (TSST-1), a bacterial superantigen. Cultures con tained allogenic irradiated feeder cells and interleukin (IL)-2, in th e absence or presence of exogenous IL-4, interferon (IFN)-gamma or IL- 12. The resulting CD4(+) T cell clones generated under these different experimental conditions were then analyzed for their ability to produ ce IL-2. IL-4, IL-5, IL-10, IFN-gamma and tumor necrosis factor (TNF)- beta in response to stimulation with phorbol 12-myristate 13-acetate ( PMA)+anti-CD3 monoclonal antibody or PMA + ionomycin. Different from T cell clones generated from peripheral blood, virtually all CD4(+) T c ell clones generated from human thymocytes produced high concentration s of IL-2. IL-4 and IL-5, but no IFN-gamma, TNF-beta or IL-10. Moreove r, after activation, these clones expressed on their surface membrane both CD30 and CD40 ligand. but not the product of lymphocyte activatio n gene (LAG)-3, and provided strong helper activity for IgE synthesis by allogeneic B cells. The Th2 cytokine pattern could not be modified by the addition of IFN-gamma. However, upon addition of exogenous IL-1 2, the resulting CD4(+) thymocyte clones produced TNF-beta, IFN-gamma: and IL-10 in addition to IL-4 and IL-5. These results suggest that CD 4(+) human thymocytes have the potential to develop into cells produci ng the Th2 cytokines IL-4 and IL-5, whereas the ability to produce bot h Th1 cytokines and IL-10 is acquired only after priming with IL-12.