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Stress cytokines: pivotal proteins in immune regulatory networks
Stress cytokines: pivotal proteins in immune regulatory networks Opinion Gabriel S Panayi1, Valerie M Corrigall1 and Brian Henderson2 Stress proteins have three immunological regulatory functions: within the cell, on the cell membrane as signalling receptors, and in the extracellular environment as stress cytokines. They can activate the immune system by providing danger signals or they may downregulate immune and inflammatory responses. In addition, they can modulate immune responses by acting as chaperones for antigenic peptides while they themselves are processed and presented to T cells as self-peptides. We predict that the exploitation of the downregulatory properties of stress cytokines will have therapeutic applications in the treatment of human chronic inflammatory diseases, such as rheumatoid arthritis. Addresses 1 Academic Department of Rheumatology, Guy’s, King’s and St Thomas’ School of Medicine, Guy’s Hospital, King’s College, London, SE1 9RT, United Kingdom 2 Division of Microbial Diseases, Eastman Dental Institute, University College London, London WC1X 8KD, United Kingdom e-mail: [email protected]
Current Opinion in Immunology 2004, 16:531–534 Available online 15th June 2004 0952-7915/$ – see front matter ß 2004 Elsevier Ltd. All rights reserved. DOI 10.1016/j.coi.2004.05.017 Abbreviations BiP binding immunoglobulin protein Cpn chaperonin gp glycoprotein HSP heat-shock protein IFN interferon IL interleukin LPS lipopolysaccharide TLR Toll-like receptors TNF tumour necrosis factor
Introduction Discovered as a novel puffing pattern in the polytene chromosomes of Drosophila melanogaster, the heat shock or cell stress response is now recognized as an essential reaction to unfolded proteins. The refolding of proteins is the function of a growing number of protein families called molecular chaperones [1], which were recognized as paradoxical immunogens [2], and in the past decade have been identified as intercellular signals in immunity — acting either directly [3] or as peptide complexes [4]. Early studies suggested that molecular chaperones were cell-activating ligands [3]. It is now emerging that, in addition to this, they can also act as receptors/ www.sciencedirect.com
co-receptors for bacterial inflammogens and as negative regulators of inflammation. The paradigm proposed in this article is that cell surface and extracellular molecular chaperones act not only as intercellular broadcasters of cell stress but also as regulators of immunoinflammatory responses. This is illustrated in Figure 1. Molecular chaperones in such environments may be better classified as stress cytokines — the term that will be used hereafter.
Stress cytokines as receptors With the possible exception of heat shock protein 10 (HSP10), which resides in the mitochondria, the most important human molecular chaperones can exist on the surface of cells. Surprisingly, the receptor for the potent inflammogen Gram-negative lipopolysaccharide (LPS) contains the two molecular chaperones HSP70 and HSP90, and antibodies to HSP70 block LPS signalling [5]. The HSP90 family member glycoprotein 96 (gp96) is not a stress protein, but rather a constitutive molecular chaperone involved in surface expression of the Toll-like receptors (TLRs; [6]). Cell-surface expression of gp96 is upregulated by bacteria [7], and this protein has now been identified as a receptor for the OmpA protein of Escherichia coli [8].
Stress cytokines as pro-inflammatory mediators Induced upregulation of HSPs by a cell under stress alters cytokine gene activation. For instance, intracellular upregulation of HSP70 attenuates NF-kB expression, inhibits TNF-a, IL-1b and IL-8 production [9,10], and downregulates adhesion molecule expression (e.g. CD54; [11]). Concomitantly, HSPs are secreted into the local environment; indeed, HSP70 or HSP60 can be detected in the blood of normal individuals [12], patients with acute infection [13] and patients with coronary artery disease [14] suggesting a ’hormonal’ function for these proteins. As extracellular proteins with specific receptors, HSP60 and HSP70 target the infiltrating monocytes and induce a pro-inflammatory response [15,16]. Activation by intact stress cytokines
Extracellular chaperonin (Cpn) 60 from both bacteria and Homo sapiens (HSP60) can stimulate pro-inflammatory behaviour in various cells including monocytes/macrophages, dendritic cells and vascular endothelial cells. This behaviour includes increased cell-surface adhesion receptor expression and the release of pro-inflammatory mediators, including cytokines. The receptor(s) for human Cpn60 is CD14 and/or TLR2 and/or TLR4 Current Opinion in Immunology 2004, 16:531–534
532 Opinion
Figure 1
Anti-inflammatory Phase
Infection
Pro-inflammatory phase
Inflammation
HSP60 & HSP70
Suppression BiP transcription and production
Bacterial HSP-specific T cells
NF-κB
+ Progress of inflammation + Stimulated by homologous host peptides (altered peptide ligand)
Inflammatory cytokines
– IL-10
Hypoxia Hypoglycaemia Heat O2 radicals
–
BiP
–
IL-10
Production and secretion of BiP and (?) HSP27
HSP60, HSP70 Initiation
Progression Time
Resolution Current Opinion in Immunology
The contribution of stress cytokines to the initiation, propagation and resolution of inflammation. Pro-inflammatory pathways are shown in red and anti-inflammatory pathways are shown in blue. The temporal relationship of the various events is emphasized by the horizontal time-line. Infection or inflammation leads to the release of human HSP60 and HSP70, which can suppress production of BiP. Bacterial HSP-specific T cells are stimulated by homologous host HSP peptides (acting as altered peptide ligands) to secrete IL-10 that will dampen down the magnitude of any ongoing immune response. HSP60 and HSP70 acting via cell membrane receptors activate NF-kB and induce the production of inflammatory cytokines such as TNF-a and IL-1 while inhibiting BiP production. Ongoing inflammation stimulates the production of more host HSPs. However, the ongoing inflammation induces hypoxia, hypoglycaemia, produces reactive oxygen radicals and it may elevate local temperature. These conditions, apart from the elevated temperature, lead to the production of BiP and possibly HSP27. BiP and IL-10 (which is induced by BiP and HSP27) then downregulate inflammation.
[17]. By contrast, and depending on the species and the protein involved, bacterial Cpn60 proteins can bind to CD14 and/or TLR receptors or to, as yet, unidentified receptors. Lectin-like oxidised low density lipoprotein receptor-1 (LOX-1) binds HSP70 [18]. Curiously, high levels of circulating HSP60, sufficient to activate cells, are found in approximately one-third of the normal population, suggesting that this protein may have a humoral function as well as being involved in the pathogenesis of atheroma [14]. Chaperonin 10, which forms a complex with Cpn60, is a potent inducer of osteoclast differentiation through an unidentified receptor [19]. Exogenous human and bacterial HSP70 proteins also stimulate monocytes/macrophages and dendritic cells via a plethora of receptors, including CD14, TLRs, CD40, CD91 and LOX-1 [16,20–24]. Surprisingly, human and bacterial Current Opinion in Immunology 2004, 16:531–534
HSP70 proteins employ different domains to bind to the same human receptor, CD40 [21]. gp96 (an endoplasmic reticulum-resident protein) undergoes receptormediated endocytosis, thus activating antigen-presenting cells [25] and/or dendritic cells [26] via CD91 and/or TLR2/4. Activation by processed antigenic peptides
There is compelling evidence that the endoplasmic reticulum chaperone gp96 (also called glucose-regulated protein 94 (grp94) directly activates antigen-presenting cells and that, furthermore, it acts as an antigenic peptide carrier, mediating cross-priming of antigen-specific T lymphocytes [27]. A similar role has been ascribed to both HSP90 and HSP70 [28]. Immunisation of rats with HSP has protective effects on microbial HSP-induced www.sciencedirect.com
Stress cytokines Panayi, Corrigall and Henderson 533
arthritis [29]. T cells directed to conserved HSP epitopes mediate the protection. These T cells are cross-reactive with the homologous self-HSP and respond as if to an altered peptide ligand with the release of IL-10 [30]. The relevance of these phenomena to human arthritis is not clear but, may be a mechanism by which inflammation induced by bacteria is regulated (see Figure 1). However, it is of interest that human binding immunoglobulin protein (BiP)-responsive T cells secrete IL-10 and may have immunoregulatory function [31].
Stress cytokines as anti-inflammatory mediators By intact stress cytokine
In contrast to the pro-inflammatory response, elicited by the ‘danger’ signals, there is evidence that there are also innate ‘protection’ signals that modulate the danger signals and act as a buffer against inappropriate reactions to antigenic challenge. Two such HSPs are BiP, also called grp78, and the small molecular weight HSP27. Both of these proteins induce a strong anti-inflammatory response with sustained production of IL-10 when acting as extracellular stress cytokines. BiP further modulates inflammation by the inhibition of TNF-a secretion, reduction of the IL-1b:IL-1 receptor antagonist ratio and increased transcription of soluble TNF receptor II (TNFRII; [31]). In addition, expression of HLA-DR and CD86 is downregulated [31] and the differentiation of immature dendritic cells is inhibited [32]. A similar regulatory function for extracellular HSP60 has been suggested following increased IL-10 production when HSP60 is added in vitro to monocytes [33,34]. The IL-10 concentrations reported in these studies are, however, >100 times less than that stimulated by BiP or HSP27. Furthermore, the production of TNF-a in these studies is not reported. It is possible that HSPs may initially stimulate both anti- and pro-inflammatory cytokines, but it is their relative concentration and the temporal sequence of production of the protein that is of ultimate importance. Thus, BiP transiently upregulates TNF-a secretion within the first 24 hours of human monocyte stimulation, followed by the sustained production of IL-10 at high concentration [31]. Interestingly, activated platelets express receptors for gp96 and are thereby able to neutralise systemic gp96, especially in the blood. This interaction does not interfere with thrombin-induced platelet activation or platelet aggregation. This anti-inflammatory effect might prevent the development of autoimmunity during wound repair [35].
by T cells. Evidence for a T helper 2 (Th2)-biased maturation of T cells following BiP stimulation of naı¨ve T cells is derived from our data on BiP-specific T-cell clones cultured from peripheral blood mononuclear cells from normal individuals. BiP T-cell clones are either CD4þ or CD8þ and can produce IL-4, IL-5 or occasionally IFN-g. All clones, however, produce IL-10 [36]. This being so, these cells proliferate poorly, and this is mirrored by the low proliferative response to BiP, which is observed in peripheral blood T-cell cultures. This condition is not always countered by the addition of antiIL-10 [31], but might be partially reversed by the addition of bystander cells transfected with human CD80 in trans co-stimulation (GS Panayi et al., unpublished).
Conclusions Molecular chaperones, acting as peptide, free intact proteins and chaperones carrying intracellular peptides, are integrating factors in immunity, linking the cell stress response to immunophysiology. In addition to acting as pro-inflammatory stimuli, evidence is emerging that certain molecular chaperones, such as BiP and HSP27 are able to counteract the inflammogenic signals including those from HSPs. The interaction and regulation of HSP60 and/or HSP70 by BiP and/or HSP27 has not been investigated, but an important area of future research should be the temporal sequence in which pro- and anti-inflammatory stress cytokines are released, thereby forming a regulatory network during inflammation.
References and recommended reading Papers of particular interest, published within the annual period of review, have been highlighted as: of special interest of outstanding interest 1.
Hartl FU, Hayer-Hartl M: Molecular chaperones in the cytosol: from nascent chain to folded protein. Science 2002, 295:1852-1858.
2.
Cohen IR, Young DB: Autoimmunity, microbial immunity and the immunological homunculus. Immunol Today 1991, 12:105-110.
3.
Maguire M, Coates ARM, Henderson B: Chaperonin 60 Unfolds Its Secrets of Cellular Communication. Cell Stress Chaperones 2002, 7:317-329.
4.
Robert J: Evolution of heat shock protein and immunity. Dev Comp Immunol 2003, 27:449-464.
5.
Triantafilou K, Triantafilou M, Dedrick RL: A CD14-independent LPS receptor cluster. Nat Immunol 2001, 2:338-345.
6.
Randow F, Seed B: Endoplasmic reticulum chaperone gp96 is required for innate immunity but not cell viability. Nat Cell Biol 2001, 3:891-896.
7.
Morales H, Muharemagic A, Gantress J, Cohen N, Robert J: Bacterial stimulation upregulates the surface expression of the stress protein gp96 on B cells in the frog Xenopus. Cell Stress Chaperones 2003, 8:265-271.
8.
Prasadarao NV, Srivastava PK, Rudrabhatla RS, Kim KS, Huang SH, Sukumaran SK: Cloning and expression of the Escherichia coli K1 outer membrane protein A receptor, a gp96 homologue. Infect Immun 2003, 71:1680-1688.
9.
Yoo CG, Lee S, Lee CT, Kim YW, Han SK, Shim YS: Anti-inflammatory effect of heat shock protein induction is related to stabilization of I kappa B alpha through preventing I
By processed antigenic peptides of stress-cytokine
In addition to innate immune responses to extracellular HSPs, the presentation of HSP peptides by antigenpresenting cells also elicits an adaptive immune response www.sciencedirect.com
Current Opinion in Immunology 2004, 16:531–534
534 Opinion
kappa B kinase activation in respiratory epithelial cells. J Immunol 2000, 164:5416-5423. 10. Hall TJ: Role of hsp70 in cytokine production. Experientia 1994, 50:1048-1053. 11. Kohn G, Wong HR, Bshesh K, Zhao B, Vasi N, Denenberg A, Morris C, Stark J, Shanley TP: Heat shock inhibits tnf-induced ICAM-1 expression in human endothelial cells via I kappa kinase inhibition. Shock 2002, 17:91-97. 12. Lewthwaite J, Owen N, Coates ARM, Henderson B, Steptoe AD: Circulating heat shock protein (Hsp)60 in the plasma of British civil servants: Relationship to physiological and psychosocial stress. Circulation 2002, 106:196-201. 13. Njemini R, Lambert M, Demanet C, Mets T: Elevated serum heat-shock protein 70 levels in patients with acute infection: use of an optimized enzyme-linked immunosorbent assay. Scand J Immunol 2003, 58:664-669. 14. Xu Q, Schett G, Perschinka H, Mayr M, Egger G, Oberhollenzer F, Willeit J, Kiechl S, Wick G: Serum soluble heat shock protein 60 is elevated in subjects with atherosclerosis in a general population. Circulation 2000, 102:14-20. 15. Flohe SB, Bruggemann J, Lendemans S, Nikulina M, Meierhoff G, Flohe S, Kolb H: Human heat shock protein 60 induces maturation of dendritic cells versus a Th1-promoting phenotype. J Immunol 2003, 170:2340-2348. 16. Asea A, Rehli M, Kabingu E, Boch JA, Bare O, Auron PE, Stevenson MA, Calderwood SK: Novel signal transduction pathway utilized by extracellular HSP70: role of toll-like receptor (TLR) 2 and TLR4. J Biol Chem 2002, 277:15028-15034. 17. Tsan MF, Gao B: Cytokine function of heat shock proteins. Am J Physiol Cell Physiol 2004, 286:C739-C744. Review. 18. Lewthwaite JC, Coates AR, Tormay P, Singh M, Mascagni P, Poole S, Roberts M, Sharp L, Henderson B: Mycobacterium tuberculosis chaperonin 60.1 is a more potent cytokine stimulator than chaperonin 60.2 (Hsp 65) and contains a CD14-binding domain. Infect Immun 2001, 69:7349-7355. 19. Meghji S, White PA, Nair SP, Reddi K, Heron K, Henderson B, Zaliani A, Fossati G, Mascagni P, Hunt JF et al.: Mycobacterium tuberculosis chaperonin 10 stimulates bone resorption: A potential contributory factor in Pott’s disease. J Exp Med 1997, 186:1241-1246. 20. Asea A, Kraeft SK, Kurt-Jones EA, Stevenson MA, Chen LB, Finberg RW: HSP70 stimulates cytokine production through a CD14-dependant pathway, demonstrating its dual role as a chaperone and cytokine. Nat Med 2000, 6:435-442. 21. Becker T, Hartl FU, Wieland F: CD40, an extracellular receptor for binding and uptake of Hsp70-peptide complexes. J Cell Biol 2002, 158:1277-1285. 22. Wang Y, Kelly CG, Karttunen JT, Whittall T, Lehner PJ, Duncan L: CD40 is a cellular receptor mediating mycobacterial heat shock protein 70 stimulation of CC-chemokines. Immunity 2001, 15:971-983. 23. Basu S, Binder RJ, Ramalingam T, Srivastava PK: CD91 is a common receptor for heat shock proteins gp96, hsp90, hsp70, and calreticulin. Immunity 2001, 14:303-313.
Current Opinion in Immunology 2004, 16:531–534
24. Delneste Y, Magistrelli G, Gauchat J, Haeuw J, Aubry J, Nakamura K: Involvement of LOX-1 in dendritic cell-mediated antigen cross-presentation. Immunity 2002, 17:353-362. 25. Baker-LePain JC, Sarzotti M, Nicchitta CV: Glucose-regulated protein 94/glycoprotein 96 elicits bystander activation of CD4(R) T cell Th1 cytokine production in vivo. J Immunol 2004, 172:4195-4203. 26. Vabulas RM, Braedel S, Hilf N, Singh-Jasuja H, Herter S, Ahmad-Nejad P, Kirschning CJ, Da Costa C, Rammensee HG, Wagner H, Schild H: The endoplasmic reticulum-resident heat shock protein Gp96 activates dendritic cells via the Toll-like receptor 2/4 pathway. J Biol Chem 2002, 277:20847-20853. 27. Li Z, Dai J, Zheng H, Liu B, Caudill M: An integrated view of the roles and mechanisms of heat shock protein. Front Biosci 2002, 7:d731-d751. 28. Srivastava PK, Udono H, Blachere NE, Li Z: Heat shock proteins transfer peptides during antigen processing and CTL priming. Immunogenetics 1994, 39:93-98. 29. Van Eden W, Wendling U, Paul L, Prakken B, van Kooten P, van der Zee R: Arthritis protective regulatory potential of self-heat shock protein cross-reactive T cells. Cell Stress Chaperones 2000, 5:452-457. 30. Wendling U, Paul L, van der Zee R, Prakken B, Singh M, van Eden W: A conserved mycobacterial heat shock protein (hsp) 70 sequence prevents adjuvant arthritis upon nasal administration and induces IL-10-producing T cells that cross-react with the mammalian self-hsp70 homologue. J Immunol 2000, 164:2711-2717. 31. Corrigall VM, Bodman-Smith MD, Brunst M, Cornell H, Panayi GS: Inhibition of antigen-presenting cell function and stimulation of human peripheral blood mononuclear cells to express an antiinflammatory cytokine profile by the stress protein BiP: relevance to the treatment of inflammatory arthritis. Arthritis Rheum 2004, 50:1164-1171. 32. Vittecoq O, Corrigall VM, Bodman-Smith MD, Panayi GS: The molecular chaperone BiP (GRP78) inhibits the differentiation of normal human monocytes into immature dendritic cells. Rheumatology (Oxford) 2003, 42(suppl):43. 33. MacHt LM, Elson CJ, Kirwan JR, Gaston JS, Lamont AG, Thompson JM, Thompson SJ: Relationship between disease severity and responses by blood mononuclear cells from patients with rheumatoid arthritis to human heat-shock protein60. Immunology 2000, 99:208-214. 34. de Kleer IM, Kamphuis SM, Rijkers GT, Scholtens L, Gordon G, De Jager W, Hafner R, van de Zee R, van Eden W, Kuis W, Prakken BJ: The spontaneous remission of juvenile idiopathic arthritis is characterized by CD30R T cells directed to human heat-shock protein 60 capable of producing the regulatory cytokine interleukin-10. Arthritis Rheum 2003, 48:2001-2010. 35. Hilf N, Singh-Jasuja H, Schwarzmaier P, Gouttefangeas C, Rammensee HG, Schild H: Human platelets express heat shock protein receptors and regulate dendritic cell maturation. Blood 2002, 99:3676-3682. 36. Bodman-Smith MD, Corrigall VM, Kemeny DM, Panayi GS: BiP, a putative autoantigen in rheumatoid arthritis, stimulates IL-10-producing CD8-positive T cells from normal individuals. Rheumatology (Oxford) 2003, 42:637-644.
www.sciencedirect.com
Current Opinion in Immunology 2004, 16:531–534 Available online 15th June 2004 0952-7915/$ – see front matter ß 2004 Elsevier Ltd. All rights reserved. DOI 10.1016/j.coi.2004.05.017 Abbreviations BiP binding immunoglobulin protein Cpn chaperonin gp glycoprotein HSP heat-shock protein IFN interferon IL interleukin LPS lipopolysaccharide TLR Toll-like receptors TNF tumour necrosis factor
Introduction Discovered as a novel puffing pattern in the polytene chromosomes of Drosophila melanogaster, the heat shock or cell stress response is now recognized as an essential reaction to unfolded proteins. The refolding of proteins is the function of a growing number of protein families called molecular chaperones [1], which were recognized as paradoxical immunogens [2], and in the past decade have been identified as intercellular signals in immunity — acting either directly [3] or as peptide complexes [4]. Early studies suggested that molecular chaperones were cell-activating ligands [3]. It is now emerging that, in addition to this, they can also act as receptors/ www.sciencedirect.com
co-receptors for bacterial inflammogens and as negative regulators of inflammation. The paradigm proposed in this article is that cell surface and extracellular molecular chaperones act not only as intercellular broadcasters of cell stress but also as regulators of immunoinflammatory responses. This is illustrated in Figure 1. Molecular chaperones in such environments may be better classified as stress cytokines — the term that will be used hereafter.
Stress cytokines as receptors With the possible exception of heat shock protein 10 (HSP10), which resides in the mitochondria, the most important human molecular chaperones can exist on the surface of cells. Surprisingly, the receptor for the potent inflammogen Gram-negative lipopolysaccharide (LPS) contains the two molecular chaperones HSP70 and HSP90, and antibodies to HSP70 block LPS signalling [5]. The HSP90 family member glycoprotein 96 (gp96) is not a stress protein, but rather a constitutive molecular chaperone involved in surface expression of the Toll-like receptors (TLRs; [6]). Cell-surface expression of gp96 is upregulated by bacteria [7], and this protein has now been identified as a receptor for the OmpA protein of Escherichia coli [8].
Stress cytokines as pro-inflammatory mediators Induced upregulation of HSPs by a cell under stress alters cytokine gene activation. For instance, intracellular upregulation of HSP70 attenuates NF-kB expression, inhibits TNF-a, IL-1b and IL-8 production [9,10], and downregulates adhesion molecule expression (e.g. CD54; [11]). Concomitantly, HSPs are secreted into the local environment; indeed, HSP70 or HSP60 can be detected in the blood of normal individuals [12], patients with acute infection [13] and patients with coronary artery disease [14] suggesting a ’hormonal’ function for these proteins. As extracellular proteins with specific receptors, HSP60 and HSP70 target the infiltrating monocytes and induce a pro-inflammatory response [15,16]. Activation by intact stress cytokines
Extracellular chaperonin (Cpn) 60 from both bacteria and Homo sapiens (HSP60) can stimulate pro-inflammatory behaviour in various cells including monocytes/macrophages, dendritic cells and vascular endothelial cells. This behaviour includes increased cell-surface adhesion receptor expression and the release of pro-inflammatory mediators, including cytokines. The receptor(s) for human Cpn60 is CD14 and/or TLR2 and/or TLR4 Current Opinion in Immunology 2004, 16:531–534
532 Opinion
Figure 1
Anti-inflammatory Phase
Infection
Pro-inflammatory phase
Inflammation
HSP60 & HSP70
Suppression BiP transcription and production
Bacterial HSP-specific T cells
NF-κB
+ Progress of inflammation + Stimulated by homologous host peptides (altered peptide ligand)
Inflammatory cytokines
– IL-10
Hypoxia Hypoglycaemia Heat O2 radicals
–
BiP
–
IL-10
Production and secretion of BiP and (?) HSP27
HSP60, HSP70 Initiation
Progression Time
Resolution Current Opinion in Immunology
The contribution of stress cytokines to the initiation, propagation and resolution of inflammation. Pro-inflammatory pathways are shown in red and anti-inflammatory pathways are shown in blue. The temporal relationship of the various events is emphasized by the horizontal time-line. Infection or inflammation leads to the release of human HSP60 and HSP70, which can suppress production of BiP. Bacterial HSP-specific T cells are stimulated by homologous host HSP peptides (acting as altered peptide ligands) to secrete IL-10 that will dampen down the magnitude of any ongoing immune response. HSP60 and HSP70 acting via cell membrane receptors activate NF-kB and induce the production of inflammatory cytokines such as TNF-a and IL-1 while inhibiting BiP production. Ongoing inflammation stimulates the production of more host HSPs. However, the ongoing inflammation induces hypoxia, hypoglycaemia, produces reactive oxygen radicals and it may elevate local temperature. These conditions, apart from the elevated temperature, lead to the production of BiP and possibly HSP27. BiP and IL-10 (which is induced by BiP and HSP27) then downregulate inflammation.
[17]. By contrast, and depending on the species and the protein involved, bacterial Cpn60 proteins can bind to CD14 and/or TLR receptors or to, as yet, unidentified receptors. Lectin-like oxidised low density lipoprotein receptor-1 (LOX-1) binds HSP70 [18]. Curiously, high levels of circulating HSP60, sufficient to activate cells, are found in approximately one-third of the normal population, suggesting that this protein may have a humoral function as well as being involved in the pathogenesis of atheroma [14]. Chaperonin 10, which forms a complex with Cpn60, is a potent inducer of osteoclast differentiation through an unidentified receptor [19]. Exogenous human and bacterial HSP70 proteins also stimulate monocytes/macrophages and dendritic cells via a plethora of receptors, including CD14, TLRs, CD40, CD91 and LOX-1 [16,20–24]. Surprisingly, human and bacterial Current Opinion in Immunology 2004, 16:531–534
HSP70 proteins employ different domains to bind to the same human receptor, CD40 [21]. gp96 (an endoplasmic reticulum-resident protein) undergoes receptormediated endocytosis, thus activating antigen-presenting cells [25] and/or dendritic cells [26] via CD91 and/or TLR2/4. Activation by processed antigenic peptides
There is compelling evidence that the endoplasmic reticulum chaperone gp96 (also called glucose-regulated protein 94 (grp94) directly activates antigen-presenting cells and that, furthermore, it acts as an antigenic peptide carrier, mediating cross-priming of antigen-specific T lymphocytes [27]. A similar role has been ascribed to both HSP90 and HSP70 [28]. Immunisation of rats with HSP has protective effects on microbial HSP-induced www.sciencedirect.com
Stress cytokines Panayi, Corrigall and Henderson 533
arthritis [29]. T cells directed to conserved HSP epitopes mediate the protection. These T cells are cross-reactive with the homologous self-HSP and respond as if to an altered peptide ligand with the release of IL-10 [30]. The relevance of these phenomena to human arthritis is not clear but, may be a mechanism by which inflammation induced by bacteria is regulated (see Figure 1). However, it is of interest that human binding immunoglobulin protein (BiP)-responsive T cells secrete IL-10 and may have immunoregulatory function [31].
Stress cytokines as anti-inflammatory mediators By intact stress cytokine
In contrast to the pro-inflammatory response, elicited by the ‘danger’ signals, there is evidence that there are also innate ‘protection’ signals that modulate the danger signals and act as a buffer against inappropriate reactions to antigenic challenge. Two such HSPs are BiP, also called grp78, and the small molecular weight HSP27. Both of these proteins induce a strong anti-inflammatory response with sustained production of IL-10 when acting as extracellular stress cytokines. BiP further modulates inflammation by the inhibition of TNF-a secretion, reduction of the IL-1b:IL-1 receptor antagonist ratio and increased transcription of soluble TNF receptor II (TNFRII; [31]). In addition, expression of HLA-DR and CD86 is downregulated [31] and the differentiation of immature dendritic cells is inhibited [32]. A similar regulatory function for extracellular HSP60 has been suggested following increased IL-10 production when HSP60 is added in vitro to monocytes [33,34]. The IL-10 concentrations reported in these studies are, however, >100 times less than that stimulated by BiP or HSP27. Furthermore, the production of TNF-a in these studies is not reported. It is possible that HSPs may initially stimulate both anti- and pro-inflammatory cytokines, but it is their relative concentration and the temporal sequence of production of the protein that is of ultimate importance. Thus, BiP transiently upregulates TNF-a secretion within the first 24 hours of human monocyte stimulation, followed by the sustained production of IL-10 at high concentration [31]. Interestingly, activated platelets express receptors for gp96 and are thereby able to neutralise systemic gp96, especially in the blood. This interaction does not interfere with thrombin-induced platelet activation or platelet aggregation. This anti-inflammatory effect might prevent the development of autoimmunity during wound repair [35].
by T cells. Evidence for a T helper 2 (Th2)-biased maturation of T cells following BiP stimulation of naı¨ve T cells is derived from our data on BiP-specific T-cell clones cultured from peripheral blood mononuclear cells from normal individuals. BiP T-cell clones are either CD4þ or CD8þ and can produce IL-4, IL-5 or occasionally IFN-g. All clones, however, produce IL-10 [36]. This being so, these cells proliferate poorly, and this is mirrored by the low proliferative response to BiP, which is observed in peripheral blood T-cell cultures. This condition is not always countered by the addition of antiIL-10 [31], but might be partially reversed by the addition of bystander cells transfected with human CD80 in trans co-stimulation (GS Panayi et al., unpublished).
Conclusions Molecular chaperones, acting as peptide, free intact proteins and chaperones carrying intracellular peptides, are integrating factors in immunity, linking the cell stress response to immunophysiology. In addition to acting as pro-inflammatory stimuli, evidence is emerging that certain molecular chaperones, such as BiP and HSP27 are able to counteract the inflammogenic signals including those from HSPs. The interaction and regulation of HSP60 and/or HSP70 by BiP and/or HSP27 has not been investigated, but an important area of future research should be the temporal sequence in which pro- and anti-inflammatory stress cytokines are released, thereby forming a regulatory network during inflammation.
References and recommended reading Papers of particular interest, published within the annual period of review, have been highlighted as: of special interest of outstanding interest 1.
Hartl FU, Hayer-Hartl M: Molecular chaperones in the cytosol: from nascent chain to folded protein. Science 2002, 295:1852-1858.
2.
Cohen IR, Young DB: Autoimmunity, microbial immunity and the immunological homunculus. Immunol Today 1991, 12:105-110.
3.
Maguire M, Coates ARM, Henderson B: Chaperonin 60 Unfolds Its Secrets of Cellular Communication. Cell Stress Chaperones 2002, 7:317-329.
4.
Robert J: Evolution of heat shock protein and immunity. Dev Comp Immunol 2003, 27:449-464.
5.
Triantafilou K, Triantafilou M, Dedrick RL: A CD14-independent LPS receptor cluster. Nat Immunol 2001, 2:338-345.
6.
Randow F, Seed B: Endoplasmic reticulum chaperone gp96 is required for innate immunity but not cell viability. Nat Cell Biol 2001, 3:891-896.
7.
Morales H, Muharemagic A, Gantress J, Cohen N, Robert J: Bacterial stimulation upregulates the surface expression of the stress protein gp96 on B cells in the frog Xenopus. Cell Stress Chaperones 2003, 8:265-271.
8.
Prasadarao NV, Srivastava PK, Rudrabhatla RS, Kim KS, Huang SH, Sukumaran SK: Cloning and expression of the Escherichia coli K1 outer membrane protein A receptor, a gp96 homologue. Infect Immun 2003, 71:1680-1688.
9.
Yoo CG, Lee S, Lee CT, Kim YW, Han SK, Shim YS: Anti-inflammatory effect of heat shock protein induction is related to stabilization of I kappa B alpha through preventing I
By processed antigenic peptides of stress-cytokine
In addition to innate immune responses to extracellular HSPs, the presentation of HSP peptides by antigenpresenting cells also elicits an adaptive immune response www.sciencedirect.com
Current Opinion in Immunology 2004, 16:531–534
534 Opinion
kappa B kinase activation in respiratory epithelial cells. J Immunol 2000, 164:5416-5423. 10. Hall TJ: Role of hsp70 in cytokine production. Experientia 1994, 50:1048-1053. 11. Kohn G, Wong HR, Bshesh K, Zhao B, Vasi N, Denenberg A, Morris C, Stark J, Shanley TP: Heat shock inhibits tnf-induced ICAM-1 expression in human endothelial cells via I kappa kinase inhibition. Shock 2002, 17:91-97. 12. Lewthwaite J, Owen N, Coates ARM, Henderson B, Steptoe AD: Circulating heat shock protein (Hsp)60 in the plasma of British civil servants: Relationship to physiological and psychosocial stress. Circulation 2002, 106:196-201. 13. Njemini R, Lambert M, Demanet C, Mets T: Elevated serum heat-shock protein 70 levels in patients with acute infection: use of an optimized enzyme-linked immunosorbent assay. Scand J Immunol 2003, 58:664-669. 14. Xu Q, Schett G, Perschinka H, Mayr M, Egger G, Oberhollenzer F, Willeit J, Kiechl S, Wick G: Serum soluble heat shock protein 60 is elevated in subjects with atherosclerosis in a general population. Circulation 2000, 102:14-20. 15. Flohe SB, Bruggemann J, Lendemans S, Nikulina M, Meierhoff G, Flohe S, Kolb H: Human heat shock protein 60 induces maturation of dendritic cells versus a Th1-promoting phenotype. J Immunol 2003, 170:2340-2348. 16. Asea A, Rehli M, Kabingu E, Boch JA, Bare O, Auron PE, Stevenson MA, Calderwood SK: Novel signal transduction pathway utilized by extracellular HSP70: role of toll-like receptor (TLR) 2 and TLR4. J Biol Chem 2002, 277:15028-15034. 17. Tsan MF, Gao B: Cytokine function of heat shock proteins. Am J Physiol Cell Physiol 2004, 286:C739-C744. Review. 18. Lewthwaite JC, Coates AR, Tormay P, Singh M, Mascagni P, Poole S, Roberts M, Sharp L, Henderson B: Mycobacterium tuberculosis chaperonin 60.1 is a more potent cytokine stimulator than chaperonin 60.2 (Hsp 65) and contains a CD14-binding domain. Infect Immun 2001, 69:7349-7355. 19. Meghji S, White PA, Nair SP, Reddi K, Heron K, Henderson B, Zaliani A, Fossati G, Mascagni P, Hunt JF et al.: Mycobacterium tuberculosis chaperonin 10 stimulates bone resorption: A potential contributory factor in Pott’s disease. J Exp Med 1997, 186:1241-1246. 20. Asea A, Kraeft SK, Kurt-Jones EA, Stevenson MA, Chen LB, Finberg RW: HSP70 stimulates cytokine production through a CD14-dependant pathway, demonstrating its dual role as a chaperone and cytokine. Nat Med 2000, 6:435-442. 21. Becker T, Hartl FU, Wieland F: CD40, an extracellular receptor for binding and uptake of Hsp70-peptide complexes. J Cell Biol 2002, 158:1277-1285. 22. Wang Y, Kelly CG, Karttunen JT, Whittall T, Lehner PJ, Duncan L: CD40 is a cellular receptor mediating mycobacterial heat shock protein 70 stimulation of CC-chemokines. Immunity 2001, 15:971-983. 23. Basu S, Binder RJ, Ramalingam T, Srivastava PK: CD91 is a common receptor for heat shock proteins gp96, hsp90, hsp70, and calreticulin. Immunity 2001, 14:303-313.
Current Opinion in Immunology 2004, 16:531–534
24. Delneste Y, Magistrelli G, Gauchat J, Haeuw J, Aubry J, Nakamura K: Involvement of LOX-1 in dendritic cell-mediated antigen cross-presentation. Immunity 2002, 17:353-362. 25. Baker-LePain JC, Sarzotti M, Nicchitta CV: Glucose-regulated protein 94/glycoprotein 96 elicits bystander activation of CD4(R) T cell Th1 cytokine production in vivo. J Immunol 2004, 172:4195-4203. 26. Vabulas RM, Braedel S, Hilf N, Singh-Jasuja H, Herter S, Ahmad-Nejad P, Kirschning CJ, Da Costa C, Rammensee HG, Wagner H, Schild H: The endoplasmic reticulum-resident heat shock protein Gp96 activates dendritic cells via the Toll-like receptor 2/4 pathway. J Biol Chem 2002, 277:20847-20853. 27. Li Z, Dai J, Zheng H, Liu B, Caudill M: An integrated view of the roles and mechanisms of heat shock protein. Front Biosci 2002, 7:d731-d751. 28. Srivastava PK, Udono H, Blachere NE, Li Z: Heat shock proteins transfer peptides during antigen processing and CTL priming. Immunogenetics 1994, 39:93-98. 29. Van Eden W, Wendling U, Paul L, Prakken B, van Kooten P, van der Zee R: Arthritis protective regulatory potential of self-heat shock protein cross-reactive T cells. Cell Stress Chaperones 2000, 5:452-457. 30. Wendling U, Paul L, van der Zee R, Prakken B, Singh M, van Eden W: A conserved mycobacterial heat shock protein (hsp) 70 sequence prevents adjuvant arthritis upon nasal administration and induces IL-10-producing T cells that cross-react with the mammalian self-hsp70 homologue. J Immunol 2000, 164:2711-2717. 31. Corrigall VM, Bodman-Smith MD, Brunst M, Cornell H, Panayi GS: Inhibition of antigen-presenting cell function and stimulation of human peripheral blood mononuclear cells to express an antiinflammatory cytokine profile by the stress protein BiP: relevance to the treatment of inflammatory arthritis. Arthritis Rheum 2004, 50:1164-1171. 32. Vittecoq O, Corrigall VM, Bodman-Smith MD, Panayi GS: The molecular chaperone BiP (GRP78) inhibits the differentiation of normal human monocytes into immature dendritic cells. Rheumatology (Oxford) 2003, 42(suppl):43. 33. MacHt LM, Elson CJ, Kirwan JR, Gaston JS, Lamont AG, Thompson JM, Thompson SJ: Relationship between disease severity and responses by blood mononuclear cells from patients with rheumatoid arthritis to human heat-shock protein60. Immunology 2000, 99:208-214. 34. de Kleer IM, Kamphuis SM, Rijkers GT, Scholtens L, Gordon G, De Jager W, Hafner R, van de Zee R, van Eden W, Kuis W, Prakken BJ: The spontaneous remission of juvenile idiopathic arthritis is characterized by CD30R T cells directed to human heat-shock protein 60 capable of producing the regulatory cytokine interleukin-10. Arthritis Rheum 2003, 48:2001-2010. 35. Hilf N, Singh-Jasuja H, Schwarzmaier P, Gouttefangeas C, Rammensee HG, Schild H: Human platelets express heat shock protein receptors and regulate dendritic cell maturation. Blood 2002, 99:3676-3682. 36. Bodman-Smith MD, Corrigall VM, Kemeny DM, Panayi GS: BiP, a putative autoantigen in rheumatoid arthritis, stimulates IL-10-producing CD8-positive T cells from normal individuals. Rheumatology (Oxford) 2003, 42:637-644.
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