Homeostatic T cell proliferati cell coculture system

Naive T cells do not proliferate in normal individuals in the absence bu of antigen stimulation, but they proliferate spontaneously when T se cells are severely depleted. We show here that coculture of syn- T geneic dendritic cells (DC) with naive T cells expressing a single T to cell receptor also results in T cell proliferation in the absence of foreign antigen. As in lymphopenic mice, where T cell proliferation M depends upon DC, this response in the coculture system requires Mi interaction of the T cells' T cell receptor with self-peptide-MHCs on ge DC. This in vitro proliferation also requires soluble factors, includ- ba ing IL-15 secreted by DC, and can be inhibited potently by cell-cell R contact with CD4+CD25+ regulatory T cells. The coculture system B( described may illuminate mechanisms that maintain stable num- th bers of T cells in normal individuals. tr R