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Differentiation of human single-positive fetal thymocytes in vitro into IL-4- and/or IFN-gamma-producing CD4+ and CD8+ T cells.

In this study we have investigated the capacity of human fetal thymocytes to differentiate in vitro into subsets of T cells with polarized Th1 or Th2 cytokine profiles. Stimulation of freshly isolated human fetal thymocytes with anti-CD3 mAb, cross-linked onto CD32,CD58,CD80-expressing mouse fibroblasts and subsequent culture in the presence of exogenous rIL-2 for 6 days, induced the production of both IL-4 and IFN-gamma, which was mainly produced by CD4+ single-positive (SP) and CD8+ SP cells respectively. Addition of rIL-4 during priming augmented IL-4 production in cultures of human fetal thymocytes, which was mainly due to an increased production of IL-4 by CD8SP cells. In contrast, addition of IL-4 to the cultures only slightly enhanced IL-4 production and had little effect on frequencies of IL-4-producing CD4SP cells. Both CD4SP and CD8SP cells produced IL-5, IL-10 and IL-13 at comparable levels, following priming in the presence of rIL-4. Priming in the presence of rIL-12 strongly enhanced the production of IFN-gamma in both CD4SP and CD8SP cells. No correlation between expression of CD27, CD30 and CD60, and a particular cytokine profile of differentiated thymocytes could be demonstrated. Together, these results demonstrate the full capacity of fetal human thymocytes to differentiate into cytokine-producing T cells in a priming milieu with appropriate stimulatory molecules and exogenous cytokines. In addition, CD4SP thymocytes rapidly differentiate into polarized Th2 cells following stimulation in vitro in the absence of exogenous rIL-4.