Presentation of self-antigens on MHC class II molecules during dendritic cell maturation.

Little is known about how dendritic cells (DCs) maintain a balance between tolerance and immunity for antigens synthesized by DCs themselves. Using transgenic DCs expressing a model self-antigen, in vitro self-peptide-MHC class II complex formation and presentation increased with DC maturation, as for exogenous antigens. In vivo, however, even 'immature' DCs isolated from steady-state lymph nodes expressed MHC at mature cell levels, although many were also CD86 low. Adoptive transfer of naive specific T cells into unstimulated transgenic mice resulted in tolerance. If the mice were also injected with anti-CD40 or Listeria monocytogenes, there was robust specific T cell expansion and inflammation. Thus, DC-endogenous antigens may induce tolerance, but only in the absence of potent maturation stimuli.