IN-VITRO MATURATION OF HUMAN NEONATAL CD4 T-LYMPHOCYTES .1. INDUCTIONOF IL-4-PRODUCING CELLS AFTER LONG-TERM CULTURE IN THE PRESENCE OF IL-4 PLUS EITHER IL-2 OR IL-12

Recent studies in the mouse have established that IL-4 and IL-12 direc t the development of Ag-stimulated naive CD4 T cells into, respectivel y, type 2 and type 1 Th cells. We report that prolonged exposure of im munologically naive and unstimulated human neonatal CD4 T cells to IL- 4 or to IL-4 plus either IL-2 or IL-12 markedly affects their cytokine production on primary stimulation with PMA and ionomycin. IL-4 induce s long-term proliferation of neonatal T cells and after 3 wk of cultur e these are capable of producing high levels of Th1 (IL-2, IFN-gamma) but no Th2 (IL-4, IL-5) cytokines; IL-4-primed cells are homogenously CD45RO-/RA+ and CD31+. After culture in the presence of IL-4 + IL-2 or IL-4 + IL-12, neonatal T cells are enriched in CD45RO+ and CD31- cell s and they can produce Th2 as well as Th1 cytokines. In response to pr imary stimulation with PMA and ionomycin, cells primed with IL-4 + IL- 2 produce IL-4, IL-5, and IL-10 and the same levels of IL-2 and IFN-ga mma as IL-4-primed cells. Cells primed with IL-4 + IL-12 produce very high levels of both IL-4 and IFN-gamma but no IL-5. Endogenous IFN-gam ma that is detected in primary cultures containing IL-4 + IL-12 does n ot inhibit, but rather enhances, the ability of the cells to produce I L-4. Further analysis of IL-4 + IL-12-primed cells reveals that IL-4 i s mainly produced by CD31- cells and that these cells can trigger B ce lls to synthesize Ig including IgE. Finally, positively selected CD31 cells remain CD31+ and are poor IL-4 producers after 3' wk of culture with IL-4 + IL-12, suggesting that these two cytokines promote the se lective expansion of the small number of CD31-cells that are present i n freshly.isolated neonatal CD4 T cells.