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Extracellular heat shock protein can deliver associated antigens into the MHC class I presentation pathway of antigen-presenting cells, a process called cross-presentation, thus inducing antigen-specific CD8+ T-cell responses; however, the precise mechanism for intracellular antigen translocation and the processing pathway has not been fully elucidated. Here we demonstrate that cross-presentation of extracellular Hsp90–ovalbumin (OVA) protein complexes to specific CD8+ T cells involves both classical proteasome–transporter-associated antigen processing (TAP)-dependent and TAP-independent–endosomal pathways. Using confocal microscopy, we found that the internalized extracellular Hsp90 and OVA co-localized with cytosolic proteasomes. When anti-Hsp90 mAb was introduced to dendritic cells (DCs), we observed that the co-localization of internalized Hsp90-chaperoned OVA and proteasomes was abolished, resulting in the inhibition of TAP-dependent cross-presentation of OVA. Thus, extracellular Hsp90 may play a pivotal role for the translocation of chaperoned antigens for proteasomal degradation in the cytosol. In contrast, OVA chaperoned by Hsp90 was not presented by MHC class II molecules in vitro or in vivo, although the antigen was exogenously loaded onto DCs. Our data indicate that extracellular Hsp90 might be essential for the translocation of chaperoned antigens from the extracellular milieu into cytosol, resulting in proteasomal degradation for cross-presentation. [ABSTRACT FROM PUBLISHER]

Immunization with heat-shock protein (HSP) gp96 elicits protective immunity to the cancer or virus-infected cells from which it is derived. Low doses of gp96 generate immunity, while doses 10 times the immunizing dose do not. We show here that injection of high doses of gp96 generates CD4+ T cells that down-regulate a variety of ongoing immune responses. Immunization with high doses of gp96 prevents myelin basic protein- or proteolipid protein-induced autoimmune encephalomyelitis in SJL mice and the onset of diabetes in non-obese diabetic mice. The suppression of immune response can be adoptively transferred with CD4+ cells and does not partition with the CD25 phenotype. The immunomodulatory properties of gp96 (and possibly other HSP) may be used for antigen-specific activation or suppression of cellular immune responses. The latter may form the basis for novel immunotherapies for autoimmune diseases. [ABSTRACT FROM AUTHOR]

Human Hsp60 (hHsp60) elicits a potent pro‐inflammatory response in cells of the innate immune system. Here we compared the capacity of peritoneal exudate cells (PEC) and bone marrow‐derived dendritic cells (DC) to stimulate murine T cells in the presence of Hsp60. Hsp60 induced a specific secretion of high amounts of IFN‐γ in T cells with PEC as antigen‐presenting cells (APC). Although DC are highly efficient APC, they were much less potent as inducers of IFN‐γ in the presence of Hsp60. The IFN‐γ‐inducing effect of Hsp60 is dependent on co‐stimulatory signals provided by B7–CD28 interactions. In addition to hHsp60, we used syngenic murine recombinant Hsp60 (mHsp60) and show that mHsp60 also induces IFN‐γ in TCR transgenic T cells. These results demonstrate that mHsp60 as an endogenous ‘self’ molecule can induce an inflammatory response. Interestingly, mHsp60, although sharing >98% protein sequence identity with the hHsp60 homologue, does not bind to human CD14 molecules. Taken together, our results indicate a finely tuned activation of cells from the innate and adaptive immune system by ‘self’ Hsp60 that depends strongly on the type of APC. [ABSTRACT FROM PUBLISHER]

Heat shock proteins (HSP) like Hsp60, Hsp70 and gp96 act directly on antigen-presenting cells (APC), e.g. by inducing the secretion of cytokines. Here we analyzed the impact of Hsp60 on the antigen-specific activation of CD8+ T cells in a TCR transgenic system. Hsp60 induced low amounts of IFN-γ in the absence of antigenic peptide; however, the release of IFN-γ is increased by a factor of 3–10 following the addition of Hsp60 to purified populations of OT-1 [ovalbumin (OVA)257–264/H2-Kb-restricted] T cells and antigen-pulsed peritoneal exudate cells (PEC) as APC. This effect is strictly correlated with the PEC ability to produce IL-12. In contrast, antigen-specific IL-2 secretion and T cell proliferation was not changed in the presence of Hsp60. Hsp60-containing OT-1 T cell cultures produced IFN-γ even when the number of antigenic MHC class I complexes was too low to be stimulatory and could not be detected with specific mAb. Hsp60, thus, acts as a catalyzing molecule to initiate both innate and adaptive immune responses, and its presence (e.g. during an infection with cellular destruction) has direct consequences for the activation of otherwise `ignorant' antigen-specific T cells. [ABSTRACT FROM PUBLISHER]

The Trypanosoma cruzi HSP70 recombinant protein has the capacity to stimulate splenocytes or lymph node cells from naive mice in a non-haplotype-restricted way. The proliferative response is abolished by proteinase K digestion and by specific anti-HSP70 antibodies. The induced stimulation index was maximal after 24 h of incubation with the protein. This stimulation leads to cell death in a Fas–Fas ligand-independent way. The phenotype of the expanded cells was CD3+ TCRαβ+ CD4+. HSP70-responsive cells express a broad range of cytokines including IFN-γ, IL-2 and tumor necrosis factor-α. After 48 h of incubation with HSP70 there was a significant increase in relative intracellular levels of CD3 TCRαβ receptors. The expanded CD4+ cell population expressed CD25; however, in contrast to concanavalin A-treated culture, delayed CD44 expression was observed. [ABSTRACT FROM PUBLISHER]