Activation of cloned human CD4+ Th1 and Th2 cells by blood dendritic cells.

Dendritic cells (DC) have been reported to be the most potent antigen-presenting cells (APC) for the activation of naive T cells and to be 10-100-fold more potent APC than monocytes (M phi) in the mixed lymphocyte reaction. In this study the authors compared human blood DC with M phi and B cells for their ability to activate cloned rye grass allergen Lol p I specific CD4+ Th1 and Th2 cells. In the presence of Lol p I, all three types of APC activated Th1 and Th2 cells to a similar extent, as shown by T-cell proliferation and interferon-gamma, interleukin-2 (IL-2) or IL-4 secretion. However, at low APC:T cell ratios, M phi were the most potent APC for both Th1 and Th2 cells followed in decreasing order by DC and B cells. This hierarchy was observed with APC preparations isolated by negative selection or highly purified by positive selection using fluorescent cell sorting for HLA-DR(high)-DC, CD14(pos)-M phi and CD19(pos)-B cells. The data demonstrate that, in contrast to what has been reported for naive T cells, human blood DC activate cloned memory Th1 and Th2 cells to a similar extent as M phi and B cells presumably because the requirements for activation of memory type T cells are less stringent than those for naive T cells.