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 t o differentiate in vitro into subsets of T cells with polarized T(h)1 or T( h)2 cytokine profiles. Stimulation of freshly isolated human fetal thymocyt es with anti-CD3 mAb, cross-linked onto CD32,CD58,CD80-expressing mouse fib roblasts and subsequent culture in the presence of exogenous rIL-2 for 6 da ys, induced the production of both IL-4 and IFN-gamma, which was mainly pro duced by CD4(+) single-positive (SP) and CD8(+) SP cells respectively. Addi tion 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-prod ucing CD4SP cells. Both CD4SP and CD8SP cells produced IL-5, IL-10 and IL-1 3 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, CD3 0 and CD60, and a particular cytokine profile of differentiated thymocytes could be demonstrated. Together, these results demonstrate the full capacit y of fetal human thymocytes to differentiate into cytokine-producing T cell s in a priming milieu with appropriate stimulatory molecules and exogenous cytokines, In addition, CD4SP thymocytes rapidly differentiate into polariz ed Th2 cells following stimulation in vitro in the absence of exogenous rIL -4.