The role of chaperone proteins in autoimmunity

Heat-shock or stress proteins (HSPs) are intracellular molecules that are expressed under cellular stress and have housekeeping and cytoprotective functions. Many of them act also as molecular chaperones, assisting the correct folding, stabilization, and translocation of proteins. In pathological situations, such as necrotic cell death, they can be released into the extracellular environment complexed with intact or fragmented cellular proteins. Evidence is now accumulating to indicate that, under certain circumstances, these complexes can contribute to induction of autoimmunity by receptor-mediated activation of the innate immune response (signaling the "danger") and by participation in the presentation of autoantigens for the adaptive immune response (acting as natural adjuvants). In addition, the conservation of HSPs through prokaryotes and eukaryotes, together with the increased production of host and microbial HSPs at the site of infection, has led to the proposition that these proteins may provide a link between infection and autoimmunity. This review outlines the mechanisms for the potential involvement of chaperones in the induction of autoimmune disease.