Heat shock proteins in dendritic cell activation and antigen cross-presentation

Heat shock proteins (HSPs) have been observed on surface of a variety of cells, and their levels are up-regulated under conditions of stress. However, the immunological consequences of surface HSP have not been studied. This thesis provides evidence for the role of surface expression of HSPs on activation of dendritic cells (DCs), the key components of both innate and adaptive immunity. The experiments showed that surface expression of an endoplasmic reticulum (ER) HSP, gp96, induces DC maturation, evidenced by up-regulation of major histocompatibility complex (MHC) 1, MHC II and co-stimulatory molecules and secretion of inflammatory cytokines. Evidence was provided to exclude the possibility of lipopolysaccharide (LPS) contamination in these experiments. In addition, I demonstrated that surface expression of gp96 induces DC activation in a myeloid differentiation marker 88 (MyD88)-dependent manner. ^ Previous studies using HSP-peptide complexes purified from cells or reconstituted in vitro, suggested that exogenous HSP-associated peptides can be presented to MHC I molecules on antigen-presenting cells (APCs), a process known as Antigen (Ag) cross-presentation. The expression of stress-induced HSPs is primarily regulated by heat shock factor 1 (HSF1), a transcription activator of HSPs. Hsf1−/− mice are deficient in induction of inducible HSPs. Using Hsf1 −/− mouse as an experiment model, I observed that HSF1 and its controlled HSPs are not essential in the development and basal function of immune system. DC differentiation and activation upon inflammatory stimulation or heat shock are also not dependent on HSF1. However, Ags from Hsf1 −/− cells showed much lower efficiency to be cross-presented to MHC I molecules on DCs when compared to those from wild type (WT) cells. The inefficiency of Ag cross-presentation from Hsf1−/− cells has been demonstrated in both in vitro and in vivo experiments using several Ag systems. ^ This work revealed an important immunological consequence of the surface expression of HSPs as activation of DCs. The intrinsic property of surface HSPs in activating DCs suggests that the export of HSPs must be tightly controlled physiologically. Furthermore, my work provides genetic evidence linking heat shock response to immunity, reinforces the critical role of HSPs in Ag cross-presentation to MHC I.