Figure 1.

Negative regulation of early innate immune responses by conventional T cells and Treg cells. Pathogens directly stimulate macrophages and DCs through TLR engagement. At the later phase of immune activation, these DC and macrophages prime other innate cells, such as NK cells, to amplify cytokine production. NK cells in turn further activate macrophages to produce more TNFα and other inflammatory cytokines with the potential to cause immunopathology. T cell–APC (i.e. macrophage or DC) interaction via MHC and/or other membrane ligands or receptors dampens the inflammatory innate response during pathogen clearance. Naïve T cells, Treg cells and B1 cells contribute to the inhibition of innate cells by means of, as yet, poorly defined mechanisms but probably involving both cytokines (TGF-β and IL-10) cell–cell interactions (e.g. BTLA–HVEM).