IL10 and infection: While peripheral control of inflammation has generally been attributed to adaptive Tr1 cells, which are thought to be a distinct lineage, our observations raise the intriguing hypothesis that during an acute infection, regulatory function is transiently acquired by Teff cells to control the T cell response by three mechanisms: a) autoregulation of the Teff response through upregulation of CTLA4 and PD1 which inhibit cytokine production b) cytokine switch from IFNγ to IL10 production and c) cell-extrinsic inhibition of the T cell proliferation.