Heat shock proteins 70 and 60 share common receptors which are expressed on human monocyte-derived but not epidermal dendritic cells

Heat-Induced Secretion of Heat Shock Proteins 70 and 90 Does not Affect the Expression of the Glucocorticoid Receptor in Primary Airway Cells in COPD

PURPOSE

The response to glucocorticoids is hampered in many COPD patients by a yet unknown mechanism. Earlier we reported that short-term heat exposure of primary human bronchial epithelial cells (BEC) and airway smooth muscle cells (ASMC) of asthma patients increased the expression and secretion of extracellular heat shock proteins (eHSPs) resulting in increased expression of glucocorticoid receptor (GR) in BEC and inhibition of ASMC remodeling. The aim of the present study was to assess if the same mechanism is also present in primary airway wall cells of COPD patients.

METHODS

Primary BEC and ASMC were established from endobronchial biopsies obtained from COPD patients (n = 73), who participated in the HISTORIC study, an investigator-initiated and driven clinical trial. Secretion and protein expression of HSPs was assessed by ELISA and Western blotting. Expression of total GR, its isoforms GRα and GRβ and toll-like receptor 4 (TLR4) was determined by Western-blotting.

RESULTS

Short heat exposure (65 °C, 10 s) of BEC resulted in a significant increase of the secretion of eHSP70 and eHSP90, while the intracellular protein was not altered. Heat treatment or exposure to eHSP70 or eHSP90 had no effect on the expression of GR and GR-isoforms. However, eHSP70 and eHSP90 significantly reduced the expression of TLR4.

CONCLUSIONS

The results of this study indicate that primary airway cells from COPD patients respond differently to heat exposure and extracellular HSP70 or HSP90 than cells from asthma patients regarding the expression of GR and this may explain the reduced response to glucocorticoids in patients with COPD.

TRIAL REGISTRATION

ISRCTN11017699.

Extracellular HSPs: The Potential Target for Human Disease Therapy

Heat shock proteins (HSPs) are highly conserved stress proteins known as molecular chaperones, which are considered to be cytoplasmic proteins with functions restricted to the intracellular compartment, such as the cytoplasm or cellular organelles. However, an increasing number of observations have shown that HSPs can also be released into the extracellular matrix and can play important roles in the modulation of inflammation and immune responses. Recent studies have demonstrated that extracellular HSPs (eHSPs) were involved in many human diseases, such as cancers, neurodegenerative diseases, and kidney diseases, which are all diseases that are closely linked to inflammation and immunity. In this review, we describe the types of eHSPs, discuss the mechanisms of eHSPs secretion, and then highlight their functions in the modulation of inflammation and immune responses. Finally, we take cancer as an example and discuss the possibility of targeting eHSPs for human disease therapy. A broader understanding of the function of eHSPs in development and progression of human disease is essential for developing new strategies to treat many human diseases that are critically related to inflammation and immunity.

Removal of DNA adducts

DNA adducts are associated with a number of diseases, including cancer. Based on a recent report by our group, the aim of this study was to test the hypothesis that DNA adducts can be removed by means of one or more of the following three intervention programmes: intermittent whole-body hyperthermia; detoxification; and cell repair. The number of DNA adducts and total DNA adduct concentrations were measured in 104 patients who underwent one or more of the three intervention programmes. DNA adduct assessments were carried out on extracted genomic DNA by gas-liquid chromatography, with any DNA adducts found being localised using DNA microarrays. The baseline median number of DNA adducts was 2. The follow-up median number of adducts was highly significantly lower at 0 (p < 0.000000000000003). The mean total DNA adduct concentration at baseline was 9.308 ng/mL, and highly significantly lower at follow-up at 1.553 ng/mL (p < 0.000000000000006). Of the three intervention programmes, only the intermittent whole-body hyperthermia was associated with a significant reduction in DNA adducts. This study offers support for the hypothesis that DNA adducts can be removed by intermittent whole-body hyperthermia. The intermittent hyperthermia used involved infrared-A (wavelength 700-1400 nm, or, equivalently, a frequency of 215-430 THz) being preferentially delivered to the whole body, apart from the head, for up to one hour per session, with gradual core body temperature elevation usually occurring during the first 20-30 min. These results may offer an explanation at the molecular level for other reported clinical benefits of intermittent whole-body hyperthermia.

Diet-induced elevation of circulating HSP70 may trigger cell adhesion and promote the development of atherosclerosis in rats

Although accumulating evidence indicates that heat shock protein 70 (HSP70) could be secreted into plasma and its levels have been found to have an ambiguous association with atherosclerosis, our knowledge for the exact role of circulating HSP70 in the development of atherosclerosis is still limited. In the present study, we report an adhesion-promoting effect of exogenous HSP70 and evaluate the potential involvement of elevated circulating HSP70 in the development of atherosclerosis. Time-dependent elevation of plasma HSP70 was found in diet-induced atherosclerotic rats, whose effect was investigated through further in vitro experiments. In rat aortic endothelial cell (RAEC) cultures, exogenous HSP70 incubation neither produced cell injuries by itself nor had protective effects on cell injuries caused by Ox-LDL or homocysteine. However, exogenous HSP70 administration could lead to a higher adhesion rate between rat peripheral blood monocytes (PBMCs) and RAECs. This adhesion-promoting effect appeared only when PBMCs, rather than RAECs, were pretreated with HSP70 incubation. PBMCs in an HSP70 environment released more IL-6 to supernatant, which subsequently up-regulated the expression of ICAM-1 in RAECs. These results indicate that the diet-induced elevation of circulating HSP70 could trigger cell adhesion with the help of IL-6 as a mediator, which provides a novel possible mechanism for understanding the role of circulating HSP70 in the pathogenesis of atherosclerosis.

Killer cell immunoglobulin receptor profile on CD4(+) CD28(-) T cells and their pathogenic role in non-dialysis-dependent and dialysis-dependent chronic kidney disease patients

There is a progressive increase in cardiovascular disease with declining renal function, unexplained by traditional risk factors. A CD4(+) T-cell subpopulation (CD4(+)  CD28(-) ), activated by human heat-shock protein 60 (hHSP 60), expands in patients with acute coronary syndrome and is associated with vascular damage. These cells exhibit cytotoxicity via expression of activating killer cell-immunoglobulin-like receptor KIR2DS2, mainly in the absence of inhibitory KIR2DL3. We investigated expansion of these cells and the pathogenic role of the KIR in non-dialysis-dependent chronic kidney disease (NDD-CKD) and end-stage haemodialysis-dependent renal disease (HD-ESRD) patients. CD4(+)  CD28(-) cells were present in 27% of the NDD-CKD and HD-ESRD patients (8-11% and 10-11% of CD4(+) compartment, respectively). CD4(+)  CD28(-) cells were phenotyped for KIR and DAP12 expression. Cytotoxicity was assessed by perforin and pro-inflammatory function by interferon-γ expression on CD4(+)  CD28(-) clones (NDD-CKD n = 97, HD-ESRD n = 262). Thirty-four per cent of the CD4(+)  CD28(-) cells from NDD-CKD expressed KIR2DS2 compared with 56% in HD-ESRD patients (P = 0·03). However, 20% of clones expressed KIR2DL3 in NDD-CKD compared with 7% in HD-ESRD patients (P = 0·004). DAP12 expression in CD28(-)  2DS2(+) clones was more prevalent in HD-ESRD than NDD-CKD (92% versus 60%; P < 0·001). Only 2DS2(+)  2DL3(-)  DAP12(+) clones were cytotoxic in response to hHSP 60. CD4(+)  CD28(-) cells exhibited increased KIR2DS2, reduced KIR2DL3 and increased DAP12 expression in HD-ESRD compared with NDD-CKD patients. These findings suggest a gradual loss of expression, functionality and protective role of inhibitory KIR2DL3 as well as increased cytotoxic potential of CD4(+)  C28(-) cells with progressive renal impairment. Clonal expansion of these T cells may contribute to heightened cardiovascular events in HD-ESRD.

Live cell immunogold labelling of RNA polymerase II

Labeling nuclear proteins with electron dense probes in living cells has been a major challenge due to their inability to penetrate into nuclei. We developed a lipid-based approach for delivering antibodies coupled to 0.8 nm ultrasmall gold particles into the nucleus to label RNA polymerase II. Focussed Ion Beam slicing coupled to Scanning Electron Microscopy (FIB/SEM) enabled visualization of entire cells with probe localization accuracy in the 10 nm range.

Mutations in the substrate binding site of human heat-shock protein 70 indicate specific interaction with HLA-DR outside the peptide binding groove

Heat-shock protein 70 (Hsp70)-peptide complexes are involved in MHC class I- and II-restricted antigen presentation, enabling enhanced activation of T cells. As shown previously, mammalian cytosolic Hsp70 (Hsc70) molecules interact specifically with HLA-DR molecules. This interaction might be of significance as Hsp70 molecules could transfer bound antigenic peptides in a ternary complex into the binding groove of HLA-DR molecules. The present study provides new insights into the distinct interaction of Hsp70 with HLA-DR molecules. Using a quantitative binding assay, it could be demonstrated that a point mutation of amino acids alanine 406 and valine 438 in the substrate binding pocket led to reduced peptide binding compared with the wild-type Hsp70 whereas HLA-DR binding remains unaffected. The removal of the C-terminal lid neither altered the substrate binding capacity nor the Hsp70 binding characteristics to HLA-DR. A truncated variant lacking the nucleotide binding domain showed no binding interactions with HLA-DR. Furthermore, the truncated ATPase subunit of constitutively expressed Hsc70 revealed similar binding affinities to HLA-DR compared with the complete Hsc70. Hence, it can be assumed that the Hsp70-HLA-DR interaction takes place outside the peptide binding groove and is attributed to the ATPase domain of HSP70 molecules. The Hsp70-chaperoned peptides might thereby be directly transferred into the binding groove of HLA-DR, so enabling enhanced presentation of the peptide on antigen-presenting cells and leading to an improved proliferation of responding T cells as shown previously.

CD91-Dependent Modulation of Immune Responses by Heat Shock Proteins: A Role in Autoimmunity

Heat shock proteins (HSPs) have been known for decades for their ability to protect cells under stressful conditions. In the 1980s a new role was ascribed for several HSPs given their ability to elicit specific immune responses in the setting of cancer and infectious disease. These immune responses have primarily been harnessed for the immunotherapy of cancer in the clinical setting. However, because of the ability of HSPs to prime diverse immune responses, they have also been used for modulation of immune responses during autoimmunity. The apparent dichotomy of immune responses elicited by HSPs is discussed here on a molecular and cellular level. The potential clinical application of HSP-mediated immune responses for therapy of autoimmune diseases is reviewed.

Heat-shock protein 60 translocates to the surface of apoptotic cells and differentiated megakaryocytes and stimulates phagocytosis

Heat-shock protein 60 (Hsp60) is a highly conserved stress protein which has chaperone functions in prokaryotes and mammalian cells. Hsp60 is associated with the mitochondria and the plasma membrane through phosphorylation by protein kinase A, and is incorporated into lipid membranes as a protein-folding chaperone. Its diverse intracellular chaperone functions include the secretion of proteins where it maintains the conformation of precursors and facilitates their translocation through the plasma membrane. We report here that Hsp60 is concentrated in apoptotic membrane blebs and translocates to the surface of cells undergoing apoptosis. Hsp60 is also enriched in platelets derived from terminally differentiated megakaryocytes and expressed at the surface of senescent platelets. Furthermore, the exposure of monocytic U937 cells to Hsp60 enhanced their phagocytic activity. Our results suggests that externalized Hsp60 in apoptotic cells and senescent platelets influences events subsequent to apoptosis, such as the clearance of apoptotic cells by phagocytes.

Lectin-like oxidized low-density lipoprotein receptor-1 delivers heat shock protein 60-fused antigen into the MHC class I presentation pathway

Heat shock protein (Hsp) 60 elicits a potent proinflammatory response in the innate immune system and has been proposed as a danger signal of stressed or damaged cells to the immune system. Previous studies reported CD14, TLR2, and TLR4 as mediators of signaling but probably not of binding. Although the receptor for Hsp60 was proposed to be saturable and specific on macrophages, it is not well defined. In the current study, we found that lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), as a receptor for Hsp60, could bind and internalize Hsp60 via the C terminus of Hsp60. Yeast two-hybrid assay revealed that the second beta-sheet containing the long-loop region of LOX-1 played an important role in this interaction. Furthermore, LOX-1 might be engaged as a common receptor for different Hsp60 species. Bone marrow-derived dendritic cells could cross-present Hsp60-fused OVA Ag on MHC class I molecules via LOX-1. Inhibition of the recognition of Hsp60 by LOX-1 decreases Hsp60-mediated cross-presentation of OVA and specific CTL response and protective tumor immunity in vivo. Taken together, these results demonstrate that LOX-1 functions as a receptor for Hsp60 and is involved in the delivery of Hsp60-fused Ag into the MHC class I presentation pathway.

Polyamine compound deoxyspergualin inhibits heat shock protein-induced activation of immature dendritic cells

Polyamine compound deoxyspergualin (DSG) is a potent immunosuppressive agent that has been applied clinically for protecting graft rejection and treatment of Wegener's granulomatosis. Though DSG can bind to heat-shock proteins (HSPs) in cells, its mechanism of immunosuppressive action remains unknown. It is widely accepted that extracellular HSPs are capable of stimulating dendritic cells (DC) through cell surface receptors, leading to DC activation and cytokine release. In this study, we examined if DSG analogs could inhibit HSP70-induced DC activation. Bone marrow derived immature mouse DCs and peripheral blood mononuclear cell-derived immature human DCs were generated and incubated with Alexa 488-labeled Hsp70 in the presence of methoxyDSG (Gus-1) that had comparable HSP70-binding affinity to DSG or DSG analog GUS-7, which had much more reduced binding affinity for HSP70. The binding of HSP70 to immature DCs was analyzed by laser microscopy and flow cytometry. HSP70-induced DC activation was assessed by TNF-alpha release by enzyme-linked immunosorbent assay. Binding of Hsp70 to the cell surface of immature DCs was inhibited under the presence of Gus-1, but not under the presence of Gus-7. Immature DCs were activated and released TNF-alpha by the stimulation with HSP70 for 12 hours; however, the HSP70-induced TNF-alpha release was suppressed under the presence of Gus-1, and partially suppressed under the presence of Gus-7. Similar results were observed when immature human DCs were stimulated under the same conditions. Immunosuppressive mechanism of DSG may be explained, at least in part, by the inhibition of extracellular HSP70-DC interaction and HSP70-induced activation of immature DCs.

Differential pathways govern CD4+ CD28- T cell proinflammatory and effector responses in patients with coronary artery disease

Patients with acute coronary syndromes experience circulatory and intraplaque expansion of an aggressive and unusual CD4(+) lymphocyte subpopulation lacking the CD28 receptor. These CD4(+)CD28(-) cells produce IFN-gamma and perforin, and are thought to play an important role in coronary atheromatous plaque destabilization. Aberrant expression of killer Ig-like receptors (KIRs) in CD4(+)CD28(-) cells is broadly thought to be responsible for their cytotoxicity, but the mechanisms involved remain poorly defined. We therefore sought to investigate the mechanism and regulation of CD4(+)CD28(-) cell functionality using T cell clones (n = 536) established from patients with coronary artery disease (n = 12) and healthy volunteers (n = 3). Our functional studies demonstrated that KIR2DS2 specifically interacted with MHC class I-presenting human heat shock protein 60 (hHSP60) inducing cytotoxicity. Further investigations revealed the novel finding that hHSP60 stimulation of TCR alone could not induce a cytotoxic response, and that this response was specific and KIR dependent. Analysis of CD4(+)CD28(-)2DS2(+) clones (n = 162) showed that not all were hHSP60 cytotoxic; albeit, their prevalence correlated with coronary disease status (p = 0.017). A higher proportion of clones responded to hHSP60 by IFN-gamma compared with perforin (p = 0.008). In this study, for the first time, we define the differential regulatory pathways involved in CD4(+)CD28(-) cell proinflammatory and effector responses. We describe in this study that, contrary to previous reports, CD4(+)CD28(-) cell recognition and killing can be specific and discriminate. These results, in addition to contributing to the understanding of CD4(+)CD28(-) cell functionality, may have implications for the monitoring and management of coronary artery disease progression.

HSP70 inhibition reverses cell adhesion mediated and acquired drug resistance in multiple myeloma

Heat shock proteins (HSPs) are a super family of highly conserved molecular chaperone proteins, which are induced in response to stress. HSP70 has been demonstrated to inhibit apoptosis induced by a number of chemotherapeutic agents. Previous investigations have suggested the development of drug resistance in multiple myeloma (MM) cells after adhesion to stroma. This study used MM cell lines and primary plasma cells to determine if HSP70 had a role in development of chemo resistance. Adhesion of MM cells to either bone marrow stromal cells or fibronectin (FN) enhanced HSP70 expression. Inhibition of the HSP70 expression decreased 8226 cell adhesion to stroma or FN and induced more apoptosis in FN-adhered 8226 cells than in suspension cultures at 24 h. Further, HSP70 inhibitors enhanced melphalan-induced apoptosis and reversed melphalan-induced cell adhesion-mediated drug resistance (CAM-DR) phenotype. In addition, compared to parental cells, KNK-437, a heat shock factor inhibitor caused more apoptosis in melphalan-resistant 8226/LR5 cells and sensitized them to melphalan. Primary CD138 positive cells showed high expression of HSPA4 mRNA, and KNK-437 caused apoptosis in these cells. In conclusion, our data suggest inhibition of HSP70, reduced adhesion and caused apoptosis of both acquired and de novo drug resistant MM cells.

Expression of heat shock protein receptors on fibroblast-like synovial cells derived from rheumatoid arthritis-affected joints

We examined the membrane expression of inducible Hsp70 and HSP receptors like TLR2, TLR4, CD14, CD36, CD40 and CD91 on fibroblast-like synovial cells (SC) derived from synovial tissue in 23 patients with rheumatoid arthritis (RA), who underwent synovectomy by using flow cytometric analysis. For comparison, autologous skin fibroblasts (SF) derived from the operation wound were tested. Significantly higher Hsp70 expression was found on synovial cells than on skin fibroblasts (median SC 21.4% x SF 5.0%, P < 0.001). Both synovial cells and skin fibroblasts expressed high levels of cell surface CD91 (median SC 80.2% x SF 79.2%), however, no or low levels of CD14, CD40, TLR2, TLR4 and CD36. Further, we observed high co-expression of CD91 and Hsp70 on RA synovial cells (median 18.6%), while skin fibroblasts showed only background Hsp70 expression (median 3.9%, P < 0.001). Since we demonstrated the high prevalence of inducible Hsp70 in RA synovial fluids, we speculate that Hsp70 might be captured onto the membrane of synovial cells from the extracellular space via the CD91 receptor. The significance of the Hsp70 interaction with synovial cells via CD91 remains undefined, but may mediate other non-immune purposes.

70-kDa heat shock proteins: specific interactions with HLA-DR molecules and their peptide fragments

Heat shock protein 70 (HSP70):peptide complexes are involved in MHC class I and class II-restricted antigen presentation enabling enhanced activation of antigen-specific T cells. Here, we investigated the potential of bacterial and mammalian HSP70 molecules to interact with peptide fragments from HLA-DR and the corresponding complete HLA-DR molecules. Peptide fragments were found to interact with DnaK, the HSP70 homologue from E. coli, but less with stress-inducible human Hsp70. Only a peptide sequence exclusively found in rheumatoid arthritis-protective HLA-DR molecules did not interact with DnaK. Subsequently, we investigated the interaction of complete HLA-DR molecules with HSP70 and detected a specific HSP70:HLA-DR interaction, with highest affinity for human stress-inducible Hsp70. In contrast to the peptide fragments, no allele-specific differences in Hsp70 affinity were detected with complete HLA-DR molecules. Interaction with HLA-DR molecules was increased at lowered pH values, whereas HSP70-chaperoned peptides were released at acidic pH, thus HSP70 could serve as scanner and carrier for antigenic peptides of self or foreign origin and transfer chaperoned peptides onto MHC class II molecules in acidic late endosomal compartments. Our findings indicate that direct interaction between mammalian HSP70 and HLA-DR molecules could be involved in the HSP70-mediated enhancement of MHC class II-restricted peptide presentation and CD4(+) T cell activation.

Toxoplasma gondii: Comparison of human CD34+ and monocyte-derived dendritic cells after parasite infection

Human dendritic cells (DC) obtained in vitro from CD34(+) progenitors (CD34-DC) or blood monocytes (mo-DC) are different DC which may be used in a model of T. gondii infection. We compared the survival, infection rate and cell surface receptor expression of both DC types after living T. gondii tachyzoite infection. CD34-DC appeared less resistant to the parasite than mo-DC. At 48h post-infection, chemokine receptors responsible for DC homing and migration were absent in mo-DC, while down regulation of CCR6 and up regulation of CCR7 was observed in CD34-DC. This result, suggesting migration ability of CD34-DC, was confirmed by in vitro migration experiments against different chemokines. Tachyzoite supernatant, used as chemokine, attracted immature CD34-DC as observed by MIP3alpha, while MIP3beta, as expected, attracted mature CD34-DC. Under similar conditions, no significant difference was noticed between mature or immature mo-DC. These data indicated that CD34-DC represent an alternative model that allows migration assay of infected DC by T. gondii.

Toxoplasma gondii-derived heat shock protein 70 stimulates maturation of murine bone marrow-derived dendritic cells via Toll-like receptor 4

Toxoplasma gondii-derived heat shock protein 70 (T.g.HSP70) induced maturation of bone marrow-derived dendritic cells (DCs) of wild-type (WT) C57BL/6 mice as evidenced by an increase in surface expression of MHC class I and II molecules and costimulatory molecules such as CD40, CD80, and CD86. Functionally, decreased phagocytic ability and increased alloreactive T cell stimulatory ability were observed in T.g.HSP70-stimulated DCs. These phenotypic and functional changes of T.g.HSP70-stimulated DCs were demonstrated in Toll-like receptor (TLR) 2- and myeloid differentiation factor 88 (MyD88)-deficient but not TLR4-deficient C57BL/6 mice. DCs from WT and TLR2-deficient but not TLR4-deficient mice produced IL-12 after T.g.HSP70 stimulation. T.g.HSP70-stimulated DCs from WT, TLR2-deficient, and MyD88-deficient, but not TLR4-deficient mice expressed IFN-beta mRNA. Thus, T.g.HSP70 stimulates murine DC maturation via TLR4 through the MyD88-independent signal transduction cascade.

Functional CD1a is stabilized by exogenous lipids

Self-glycosphingolipids bind to surface CD1 molecules and are readily displaced by other CD1 ligands. This capacity to exchange antigens at the cell surface is not common to other antigen-presenting molecules and its physiological importance is unclear. Here we show that a large pool of cell-surface CD1a, but not CD1b molecules, is stabilized by exogenous lipids present in serum. Under serum deprivation CD1a molecules are altered and functionally inactive, as they are unable to present lipid antigens to T cells. Glycosphingolipids and phospholipids bind to, and restore functionality to CD1a without the contribution of newly synthesized and recycling CD1a molecules. The dependence of CD1a stability on exogenous lipids is not related to its intracellular traffic and rather to its antigen-binding pockets. These results indicate a functional dichotomy between CD1a and CD1b molecules and provide new information on how the lipid antigenic repertoire is immunologically sampled.

The heat shock protein Hsp70 enhances antigen-specific proliferation of human CD4+ memory T cells

Heat shock proteins (HSP) can interact with a wide variety of peptides and the resulting HSP:peptide complexes are known to be highly immunogenic. The ability of HSP:peptide complexes to elicit CD8+ T cell responses by cross-presentation of exogenous antigen via MHC class I is well known. In contrast, their role in the activation of CD4+ T cells is less clearly defined, although several recent studies in mice and T cell lines suggest an involvement of HSP in the presentation of antigenic peptides via MHC class II. In this study we have investigated the potential of antigenic peptides from tetanus toxin and influenza hemagglutinin complexed to the human stress-inducible Hsp70 to enhance activation and proliferation of human memory CD4+ T cells. Hsp70:peptide complexes were found to amplify the proliferation of antigen-specific CD4+ T cells as confirmed by HLA-DR tetramer staining. Complex formation of the antigenic peptide with Hsp70 was absolutely required to elicit an antigen-specific amplification. This effect was most pronounced at low doses of antigen and decreasing APC/CD4+ T cell ratios. Taken together, we show the potential of Hsp70 to enhance antigen-specific CD4+ T cell proliferation and to increase the immunogenicity of presented peptides in human CD4+ T cells.

Addicted to death: invasive cancer and the immune response to unscheduled cell death

The development of an invasive cancer involves a progressive switch from predominantly apoptotic (scheduled) to necrotic (unscheduled) tumor cell death. This switch is associated with chronic and increasing release of intracellular factors that in turn promote reactive angiogenesis and stromal proliferation and mediates the disordered tumor microenvironment associated with local immune suppression. The authors review the relevant immunobiology of these factors, including the nuclear protein HMGB1; the products of purine metabolism (uric acid, ATP, and adenosine); the S100 family members; and the heat shock proteins, which we believe drive futile cycles of cell death followed by reparative cell growth. The authors also present a novel and provocative hypothesis that suggests that most of the derangements that we associate with progression of cancer and the associated immunologic consequences can indeed be ascribed to the consequences of disordered tumor cell death rather than cell growth. Thus the fundamental defect in invasive human cancers, in the authors' view, is not one of cell growth but rather one of disordered cell death, resulting in turn in a tumor microenvironment that encourages tumor growth, progression, and local immunosuppression, a condition the authors have termed "addicted to death." This new understanding could inform and drive the development of more effective biologic therapies for patients with cancer.

A novel HBV DNA vaccine based on T cell epitopes and its potential therapeutic effect in HBV transgenic mice

DNA vaccination represents a novel therapeutic strategy for chronic hepatitis B virus (HBV) infection. Recently, some HBV DNA vaccines have been used in the preliminary clinical trials and exhibited exciting results in chronic HBV carriers. But these vaccines only encoded the single viral antigen, the S or the PreS2/S antigen. In this study, we designed a polytope DNA vaccine encoding multiple T cell epitopes. We found that it induced stronger CTL responses than the vaccine encoding the single antigen in H-2d and H-2b mice, although the CTL response to Ld-restricted epitope suppressed the CTLs to other epitopes in H-2d-restricted mice. Interestingly, heat shock protein 70 as an adjuvant not only enhanced CTL response to the viral antigen but also overcame this epitope suppression. Furthermore, the polytope DNA vaccine resulted in a long-term down-regulation of hepatitis B virus surface antigen and inhibition of HBV DNA replication in a HBV transgenic mouse model. Therefore, our research indicates that it is practicable and feasible to design a polytope DNA vaccine for chronic hepatitis B immunotherapy.

MHC class Ib molecules bridge innate and acquired immunity

Our understanding of the classical MHC class I molecules (MHC class Ia molecules) has long focused on their extreme polymorphism. These molecules present peptides to T cells and are central to discrimination between self and non-self. By contrast, the functions of the non-polymorphic MHC class I molecules (MHC class Ib molecules) have been elusive, but emerging evidence reveals that, in addition to antigen presentation, MHC class Ib molecules are involved in immunoregulation. As we discuss here, the subset of MHC class Ib molecules that presents peptides to T cells bridges innate and acquired immunity, and this provides insights into the origins of acquired immunity.

Extracellular HSP70 binding to surface receptors present on antigen presenting cells and endothelial/epithelial cells

Extracellular HSP70 has been found to participate in both innate and adaptive immune responses. However, little is known about the molecular mechanisms that mediate this process. Previous reports suggest that HSP70 interacts with antigen presenting cells (APC) through a plethora of surface receptors. In this study, we have examined the relative binding of potential HSP70 receptors and found high affinity binding to LOX-1 but not other structures with a role in HSP70-APC interactions such as LRP/CD91, CD40, TLR2, TLR4 or another c-type lectin family member (DC-SIGN) closely related to LOX-1. In addition to APC, HSP70 can avidly bind to non-APC cell lines, especially those from epithelial or endothelial background.

Mycobacterium avium ssp. paratuberculosis recombinant heat shock protein 70 interaction with different bovine antigen-presenting cells

Abstract Heat shock proteins (Hsp) can deliver antigen into the major histocompatibility complex class I presentation pathway of antigen-presenting cells (APC), a process called cross priming, thus stimulating antigen-specific CD8+ T-cell reactions. Hsp were shown to elicit proinflammatory responses in APC. Both processes require interaction of Hsp with APC via specific receptors. This study describes the interaction of recombinant Hsp70 (rHsp70) of Mycobacterium avium subspecies paratuberculosis with bovine peripheral blood mononuclear cells that was restricted to CD14+ cells. Characterized monocyte-derived macrophages, monocyte-derived dendritic cells (DC) and BoMac, an immortalized bovine macrophage cell line, were used to investigate the interaction of rHsp70 with different bovine APC. Saturation of immature DC with high concentrations of rHsp70 is demonstrated, and it was found that interaction of rHsp70 with DC was related to the maturation stage of the DC. Involvement of CD91 as a cellular receptor for rHsp70 was demonstrated; however, competition studies with immature DC demonstrated that other receptors exist on bovine APC. These data suggest that rHsp70-based vaccines may be useful for the successful immunization of cattle.

Detection of HSP60 on the membrane surface of stressed human endothelial cells by atomic force and confocal microscopy

The highly conserved and ubiquitous heat shock proteins (HSP) are essential for the cellular homeostasis and efficiently trigger cellular responses to stress conditions. Both microbial and human HSP act as dominant antigens in numerous infectious and autoimmune diseases such as atherosclerosis, inducing a strong immune-inflammatory response. In the present study, the surface localization of HSP60 on stressed and unstressed human umbilical venous endothelial cells (HUVECs) was investigated using sensitive high resolution microscopy methods and flow cytometry. Confocal laser scanning microscopy (CLSM) revealed an increase of HSP60 in the mitochondria and on the surface of heat-stressed living and fixed HUVECs compared to unstressed cells. Atomic force microscopy (AFM), which has developed as sensitive surface-probe technique in biology, confirmed the presence of HSP60 on the membrane of stressed cells at an even higher lateral resolution by detecting specific single molecule binding events between the monoclonal antibody AbII-13 tethered to AFM tips and HSP60 molecules on cells. The interaction force (force required to break a single AbII-13/HSP60 bond) was 59+/-2 pN, which correlated nicely to the 51+/-1 pN measured with isolated HSP60 attached to mica surfaces. Overall, we found clear evidence for the occurrence of HSP60 on the surface of stressed HUVECs in a very similar patchy distribution pattern in living and fixed cells. The relevance of our findings with respect to the role of HSP60 in atherogenesis is discussed.

Identification of Stimulating and Inhibitory Epitopes within the Heat Shock Protein 70 Molecule That Modulate Cytokine Production and Maturation of Dendritic Cells

The 70-kDa microbial heat shock protein (mHSP70) has a profound effect on the immune system, interacting with the CD40 receptor on DC and monocytes to produce cytokines and chemokines. The mHSP70 also induces maturation of dendritic cells (DC) and thus acts as an alternative ligand to CD40L on T cells. In this investigation, we have identified a cytokine-stimulating epitope (peptide 407-426), by activating DC with overlapping synthetic peptides (20-mers) derived from the sequence of mHSP70. This peptide also significantly enhances maturation of DC stimulated by mHSP70 or CD40L. The epitope is located at the base of the peptide-binding groove of HSP70 and has five critical residues. Furthermore, an inhibitory epitope (p457-496) was identified downstream from the peptide-binding groove that inhibits cytokine production and maturation of DC stimulated by HSP70 or CD40L. The p38 MAP kinase phosphorylation is critical in the alternative CD40-HSP70 pathway and is inhibited by p457-496 but enhanced by p407-426.

The heat-shock protein receptors: some answers and more questions

The existence of heat-shock protein (HSP) receptors on antigen-presenting cells (APCs) was hypothesized in 1994. The first such receptor, CD91 or LRP, was identified and characterized in 2000. The pace of attribution has quickened since and during the last three years alone, six putative HSP receptors have been identified. These include CD40, LOX-1, CD36, Toll-like receptor-2 (TLR-2), TLR-4 and SR-A. The literature on HSP receptors on APCs is critically examined in this review and future directions are imagined.

The common heat shock protein receptor CD91 is up-regulated on monocytes of advanced melanoma slow progressors

Despite advances in our understanding of tumour immunology there is no therapy of proven survival benefit for advanced melanoma. Nevertheless, disease progression is slow in a small proportion of patients with metastatic melanoma, suggesting a contribution to outcome from host factors. Recent data have indicated the importance of the heat shock protein receptor CD91 in immune responses to, and progression of, infectious disease. Here we investigate the relationship between CD91 expression and outcome in malignancy. Rare melanoma patients were recruited with advanced disease that was progressing unusually slowly. CD91 expression on their monocytes was compared with control patients with more typical rapidly advancing metastatic disease. Th1 and Th2 cytokines, as well as innate and adaptive immune subsets, were also measured in the two groups. A significant increase in median CD91 expression levels was observed in slow progressors (P = 0.006). There were no differences in other immune subset markers or inflammatory cytokines. The ability of CD91 to internalize and cross-present tumour antigens through the major histocompatibility complex class I pathway may maintain CD8-positive cytotoxic T cell responses and contribute to slow progression of advanced melanoma.

Secretory heat-shock protein as a dendritic cell-targeting molecule: a new strategy to enhance the potency of genetic vaccines

DNA vaccines are an appealing strategy for inducing cytotoxic T-lymphocyte and antibody responses against tumor cells as well as infectious agents. Dendritic cells (DCs) play a critical role in inducing immune responses, but their potential is not fully utilized in the DNA vaccine setting since they take up only a minor fraction of the injected DNA. Here we describe a novel DNA vaccination strategy based on the targeting of a modified tumor-associated antigen, the human papilloma virus (HPV) type 16 E7 protein, to DCs by a heat-shock protein (HSP) to enhance antigen presentation and immune responses. Specifically, a chimerical HPV-E7 and HSP70 fusion gene preceded with a leader sequence was constructed. When mice were immunized with this construct, the DNA is taken up by various types of cells, which then produce and secrete an HPV-E7-HSP70 fusion protein that is targeted to DCs by the HSP70 portion of the chimerical molecule for antigen presentation. In studies to test the efficacy of this strategy, we demonstrated that DNA vaccination with this secretory HPV-E7-HSP70 construct strongly enhanced an antigen-specific CD8+ T-cell response as well as a specific B-cell response in mice. Furthermore, this immunization approach not only protected mice against lethal challenge with an HPV E7-expressing tumor line (TC-1), but also showed a therapeutic effect against established tumors. The results of this study indicate that secretory HSPs can be broadly used to target tumor-associated antigens to DCs to enhance antigen-specific immune responses.

Recruitment of Hsp70 chaperones: a crucial part of viral survival strategies

Virus proliferation depends on the successful recruitment of host cellular components for their own replication, protein synthesis, and virion assembly. In the course of virus particle production a large number of proteins are synthesized in a relatively short time, whereby protein folding can become a limiting step. Most viruses therefore need cellular chaperones during their life cycle. In addition to their own protein folding problems viruses need to interfere with cellular processes such as signal transduction, cell cycle regulation and induction of apoptosis in order to create a favorable environment for their proliferation and to avoid premature cell death. Chaperones are involved in the control of these cellular processes and some viruses reprogram their host cell by interacting with them. Hsp70 chaperones, as central components of the cellular chaperone network, are frequently recruited by viruses. This review focuses on the function of Hsp70 chaperones at the different stages of the viral life cycle emphasizing mechanistic aspects.

Immunological aspects of heat-shock proteins-the optimum stress of life

This review summarizes the complex role of heat-shock proteins (Hsp) in immune reactions, especially the cellular effects of heat-shock proteins during the recognition processes by innate immunity. The role of heat-shock proteins in the pathogenesis of two multifactorial diseases, i.e. inflammatory bowel disease (IBD) and atherosclerosis is highlighted. A new hypothesis on "immunodeficiency burden" is presented. According to this hypothesis, susceptibility to any multifactorial disease in any given subject and in the presence of specific environmental factors is the aggregate effect of polymorphisms resulting in the failure of protective immunity with consequent disease.

DNA vaccines expressing antigens with a stress protein-capturing domain display enhanced immunogenicity

An expression system for DNA vaccines is described, in which a fusion protein with an N-terminal, viral J-domain that captures heat-shock proteins (Hsps) is translated in-frame with C-terminal antigen-encoding sequences (of various lengths and origins). The system supports enhanced expression of chimeric antigens (of >800 residues in length) with an extended half life (>8 h). When used as a DNA vaccine, it delivers antigen together with the intrinsic adjuvant activity provided by bound Hsps. We describe the design of vectors for DNA vaccination that support the expression of different immunogenic domains of different origins as large, Hsp-capturing chimeric fusion antigens. The immunogenicity of the antigens produced by this expression system (when it is built into DNA vaccines) has been characterized in detail, with particular emphasis on priming CD8+ T-cell responses. We also discuss areas of vaccine research to which the new technology may provide useful contributions.

Kaposi's sarcoma as a model for cancer immunotherapy

Physicians have, for over a century, attempted to harness the potential therapeutic power of the immune system to treat patients with cancer. The discovery that cancer regression can be achieved by immune rejection of tumour antigens theoretically allows the eradication of neoplastic cells without toxicity to normal tissues. An understanding of the mode of presentation of tumour antigens, including those complexed to heat shock proteins by major histocompatibility complex (MHC) class I and class II molecules, and their recognition by CD8(+) and CD4(+) T cells, respectively, has further delineated the potential cancer rejection pathways involved. This also enables the sustained induction and expansion of specific anti-tumour T cells with cytolytic activity.

Aberrant extracellular and dendritic cell (DC) surface expression of heat shock protein (hsp)70 in the rheumatoid joint: possible mechanisms of hsp/DC-mediated cross-priming

We describe, in rheumatoid arthritis (RA), abnormalities in the expression and distribution of heat shock protein (hsp) and dendritic cells (DCs) that are conducive to cross-priming and DC cross-talk. As detected by ELISA, inducible (i)hsp70 was dramatically increased in RA synovial fluid (RASF) vs normal human and RA sera and osteoarthritis and gout synovial fluid. Immunoblot analysis of fresh RASF cells revealed marked increases in ihsp70 and activation of its transcription factor heat shock factor-1, compared with fresh normal peripheral blood cells. Flow cytometry and microscopy demonstrated high levels of ihsp70 on the surface of RASF myeloid DCs (but not normal myeloid DCs) that occurred concurrently with hspRs (CD91/CD14). ihsp70 present in RASF exhibited chaperoning potential, as indicated by the capture of ihsp70 present in RASF on the surface of normal DCs. Binding was partially competitively inhibited by excess alpha(2)-macroglobulin, indicating that hspRs in addition to CD91 participate in the capture process. These data indicate that ihsp70 may chaperone autologous Ags into immature RASF DCs via hspRs, and that cross-talk between DCs coexpressing hsp/hspRs reflects a disease process in RA. The induction of surface ihsp70 on normal cells after sublethal heat stress and the release of ihsp70 from normal DCs after inflammatory stress also suggest that the pattern of ihsp70 expression in RASF occurs in response to sustained stress.

HSP70 Peptide Binding Mutants Separate Antigen Delivery from Dendritic Cell Stimulation

Microbial heat shock proteins (HSPs) have been implicated in the induction of both the innate and adaptive arms of the immune response. We now show that human dendritic cells (DC) pulsed with peptide-loaded mycobacterial HSP70 complexes generate potent antigen-specific cytotoxic lymphocyte (CTL) responses, which are dependent on an HSP70-stimulated calcium signaling cascade. From the calculated peptide binding affinity of mycobacterial HSP70 (K(D) = 14 microM) we show that 120 pM HSP70 bound peptide is sufficient to generate a peptide-specific CTL response that is up to four orders of magnitude more efficient than peptide alone. The minimal 136 amino acid, mycobacterial HSP70 peptide binding domain can generate CTL responses, and a single amino acid mutant HSP70 designed to prevent peptide binding but retain stimulatory capacity has allowed us to separate antigen delivery from DC immunostimulation.

Mycobacterial heat shock protein 65 enhances antigen cross-presentation in dendritic cells independent of Toll-like receptor 4 signaling

Heat shock proteins (HSP) have been shown to enhance antigen processing and presentation through their association with antigenic peptides and delivery of these moieties into major histocompatibility complex class I pathways. In this study, mycobacterial Hsp65 is demonstrated to have the ability to help cross-present an exogenous protein by dendritic cells (DC) to CD8 T cells without the need for complex formation between Hsp65 and the protein. This ability of Hsp65 to enhance cross-presentation is independent of its weak stimulatory effect on DC, the latter seen only after prolonged incubation. When the effect of lipopolysaccharide contamination is abrogated, Hsp65 is unable to activate Toll-like receptor (TLR)4 in the presence of CD14 and MD2. This accounts for the inability of Hsp65 to drive maturation of DC and shows that Hsp65 is not a potent stimulator of DC. Thus, Hsp65 enhances the cross-presentation of a soluble, free antigen by DC, independent of TLR4 signaling and up-regulation of costimulatory molecules.

Disease-associated dendritic cells respond to disease-specific antigens through the common heat shock protein receptor

The most abundant intracellular proteins, heat shock proteins (HSPs), serve as molecular chaperones for regulatory and maturation pathways. Diverse families of HSPs have been shown to bind antigenic peptides and to play major roles in innate and adaptive immune responses through the common HSP receptor, CD91. HIV-1+ patients with Kaposi sarcoma (KS) were matched for CD4 count and HIV-1 RNA viral load to HIV-1+ patients without Kaposi sarcoma (and negative for Kaposisarcoma-associated herpesvirus). We then investigated the pathways used by tumor lysates, viral lysates, and viral particles in their activation. In particular, we observed immune responses after HSP depletion using antitumor antibiotics and blockade of the common HSP receptor, CD91. Despite the impaired functional capacity of dendritic cells (DCs) derived from patients with KS, DCs retain the ability to prime the adaptive arm of the immune system through the common HSP receptor, leading to phenotypic activation and stimulation of tetramer-positive CD8+ cytotoxic T cells. We also show that interferon-producing plasmacytoid DCs are selectively depleted in KS-positive compared with matched KS-negative HIV-1-infected patients. Functionally impaired DCs can effectively cross-present immune responses through the common HSP receptor. These results have important implications for the etiopathogenesis of KS and for the development and design of any compounds, including vaccines, derived from cellular lysates.

Role for heat shock proteins in the immune response to measles virus infection

Heat shock proteins (HSPs) are recognized for their support of protein metabolism. Interaction with viral proteins also enhances the development of innate and adaptive immune responses against the infecting agent. At the level of the infected cell, HSPs are uniquely expressed on the cell surface, where they represent targets of lymphokine activated killer cells. Necrosis of the infected cell releases complexes of HSP and viral protein, which, in turn, binds antigen-presenting cells (APCs). One effect of binding is to stimulate APC maturation and the release of proinflammatory cytokines, an adjuvant effect that prepares the way for adaptive immune responses. A second effect of binding is to direct the antigenic cargo of the HSP into endogenous MHC presentation pathways for priming of naive cytotoxic T cells (CTL) or activation of antigen-specific CTLs. This alternate pathway of antigen presentation is essential to CTL priming following primary brain infection. Using heat shock to elevate brain levels of HSP in a mouse model of measles virus (MV) persistent infection, we provide evidence supporting a role for HSPs in promoting cell-mediated viral clearance from brain. The findings highlight the probable relevance of HSPs to anti-MV immunity, suggesting novel routes of both therapeutic intervention and preventative measures.

Different heat shock protein 60 species share pro-inflammatory activity but not binding sites on macrophages

In a study of seven different hsp60 species, we found that all mammalian and microbial proteins shared the property of eliciting an inflammatory response in mouse macrophages. In all cases, TNFalpha production was induced by 0.1 microM concentrations of hsp60. However, the different hsp60 preparations did not compete for the same binding site. The binding of fluorescence-labeled human hsp60 was inhibited by excess unlabeled human, rat or mouse hsp60, but not hamster, Escherichia coli, Chlamydia pneumoniae or Mycobacterium bovis hsp60. We conclude that phylogenetically separate hsp60 species interact with innate immune cells via different recognition pathways.

Making and breaking tolerance

The lymphocyte's decision between tolerance and immunity/autoimmunity is regulated at many levels. Two important parameters in this decision are the maturation state of the antigen presenting cells (APCs) and the amount of self antigen that is detected by the immune system. Maturation of APCs occurs as a consequence of signals received by the innate immune system and may lead to the breakdown of tolerance. Particularly relevant to this process are the Toll-like receptors and mechanisms of cross presentation of self antigens. In addition, genetic alterations in a variety of cell surface receptors, signalling components and regulators of apoptosis/survival can break tolerance and lead to autoimmunity in vivo.

Endotoxin-free heat-shock protein 70 fails to induce APC activation

Previous work has suggested that the peptide-carrier, heat-shock protein (hsp)70, could directly activate APC. Here we show that this ability is related to endotoxin contamination of the human rhsp70 produced in Escherichia coli. Hence, the ability of 1-3 microg/ml of rhsp70 to induce the maturation of human monocyte-derived DC is abrogated in the presence of the LPS-antagonist polymyxin B or when the rhsp70 contains less than 60 IU/mg endotoxin. Such a level of contamination of the rhsp70 is, however, sufficient - in the presence of soluble rCD14, the LPS co-receptor - to induce cytokine secretion from monocytes and DC, despite the presence of polymyxin B. However, when endotoxin contamination is below 10 IU/mg, rhsp70 does not induce cytokine secretion - even in the presence of soluble rCD14 - or activate p38 mitogen-activated protein kinase signaling pathways, thus showing that an "endotoxin free" hsp70 does not activate APC.

Induction of cyclooxygenase-2 by heat shock protein 60 in macrophages and endothelial cells

The 60-kDa heat shock protein (HSP60), an endogenous ligand for the toll-like 4 receptor, is generated in response to inflammation, tissue injury, and/or stress and stimulates macrophages to produce cytotoxic and proinflammatory mediators including nitric oxide, tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, and IL-12. In the present studies we report that HSP60 is an effective inducer of cyclooxygenase-2 (COX-2) in macrophages, as well as endothelial cells. In both cell types, the synthesis of COX-2 was coordinate with induction of nitric oxide synthase (NOS)-2 and with nitric oxide production. With the use of promoter constructs in transient transfection assays, optimal expression of COX-2 in macrophages was found to require nuclear factor (NF)-kappaB, the cAMP-response element (CRE), and NF-IL-6, but not the E-box. Mobility shift assays revealed that HSP60 induced NF-kappaB and CRE binding activity, while CCAAT/enhancer binding protein (C/EBP), which binds to NF-IL-6, was constitutively active in the cells. Both c-Jun and CRE binding protein (CREB) bound to the CRE, while C/EBP-beta bound to NF-IL-6. These data indicate that NF-kappaB, C/EBP-beta, c-Jun, and CREB are important in HSP60-induced expression of COX-2. The c-Jun-NH(2)-terminal kinase (JNK), p44/42 mitogen-activated protein (MAP) kinase [extracellular signal-regulated kinase 1/2 (ERK1/2)], and p38 MAP kinase were rapidly activated by HSP60 in the macrophages. PD-98059, an inhibitor of phosphorylation of ERK1/2, caused a marked inhibition of HSP60-induced COX-2 and NOS-2 expression. Unexpectedly, SB-203580, a p38 kinase antagonist, was found to block HSP60-induced expression of COX-2, but not NOS-2. These data indicate that both ERK1/2 kinase and p38 kinase play a role in regulating HSP60-induced expression of COX-2.

Human papillomavirus virus-like particles do not activate Langerhans cells: a possible immune escape mechanism used by human papillomaviruses

High-risk human papillomaviruses are linked to several malignancies including cervical cancer. Because human papillomavirus-infected women do not always mount protective antiviral immunity, we explored the interaction of human papillomavirus with Langerhans cells, which would be the first APCs the virus comes into contact with during infection. We determined that dendritic cells, normally targeted by vaccination procedures and Langerhans cells, normally targeted by the natural virus equally internalize human papillomavirus virus-like particles. However, in contrast to dendritic cells, Langerhans cells are not activated by human papillomavirus virus-like particles, illustrated by the lack of: up-regulating activation markers, secreting IL-12, stimulating T cells in an MLR, inducing human papillomavirus-specific immunity, and migrating from epidermal tissue. Langerhans cells, like dendritic cells, can display all of these characteristics when stimulated by proinflammatory agents. These data may define an intriguing immune escape mechanism used by human papillomavirus and form the basis for designing optimal vaccination strategies.

Involvement of LOX-1 in dendritic cell-mediated antigen cross-presentation

Some exogenous antigens, such as heat shock proteins or apoptotic bodies, gain access to the MHC class I processing pathway and initiate CTL responses, a process called cross-priming. To be efficient in vivo, this process requires endocytosis of the antigen by dendritic cells via receptors which remain unidentified. Here, we report that scavenger receptors are the main HSP binding structures on human dendritic cells and identify LOX-1 as one of these molecules. A neutralizing anti-LOX-1 mAb inhibits Hsp70 binding to dendritic cells and Hsp70-induced antigen cross-presentation. In vivo, to target LOX-1 with a tumor antigen using an anti-LOX-1 mAb induces antitumor immunity. Thus, the scavenger receptor LOX-1 is certainly a promising target for cancer immunotherapy.

Roles of heat-shock proteins in innate and adaptive immunity

Heat-shock proteins (HSPs) are the most abundant and ubiquitous soluble intracellular proteins. In single-cell organisms, invertebrates and vertebrates, they perform a multitude of housekeeping functions that are essential for cellular survival. In higher vertebrates, their ability to interact with a wide range of proteins and peptides--a property that is shared by major histocompatibility complex molecules--has made the HSPs uniquely suited to an important role in organismal survival by their participation in innate and adaptive immune responses. The immunological properties of HSPs enable them to be used in new immunotherapies of cancers and infections.