Heat-shock proteins induce T-cell regulation of chronic inflammation

Immune responses to certain heat-shock proteins (HSPs) develop in almost all inflammatory diseases; however, the significance of such responses is only now becoming clear. In experimental disease models, HSPs can prevent or arrest inflammatory damage, and in initial clinical trials in patients with chronic inflammatory disease, HSP-derived peptides have been shown to promote the production of anti-inflammatory cytokines, indicating that HSPs have immunoregulatory potential. In this Review, we discuss the unique characteristics of HSPs that endow them with these immunoregulatory qualities.

Interleukin-4 therapy of psoriasis induces Th2 responses and improves human autoimmune disease

Selective skewing of autoreactive interferon-gamma (IFN-gamma)-producing T helper cells (Th1) toward an interleukin-4 (IL-4)-producing (Th2) phenotype can in experimental animals alleviate autoimmune disease without inducing general immunosuppression. In a prospective dose escalation study, we assessed treatment with human IL-4 (rhuIL-4) in 20 patients with severe psoriasis. The therapy was well tolerated, and within six weeks all patients showed decreased clinical scores and 15 improved more than 68%. Stable reduction of clinical scores was significantly better at 0.2-0.5 microg rhuIL-4 than at < or =0.1 microg rhuIL-4 (P = 0.009). In psoriatic lesions, treatment with 0.2-0.5 microg/kg rhuIL-4 reduced the concentrations of IL-8 and IL-19, two cytokines directly involved in psoriasis; the number of chemokine receptor CCR5+ Th1 cells; and the IFN-gamma/IL-4 ratio. In the circulation, 0.2-0.5 microg/kg rhuIL-4 increased the number of IL-4+CD4+ T cells two- to three-fold. Thus, IL-4 therapy can induce Th2 differentiation in human CD4+ T cells and has promise as a potential treatment for psoriasis, a prototypic Th1-associated autoimmune disease.

Mechanisms of disease: the hygiene hypothesis revisited

In industrialized countries the incidence of diseases caused by immune dysregulation has risen. Epidemiologic studies initially suggested this was connected to a reduction in the incidence of infectious diseases; however, an association with defects in immunoregulation is now being recognized. Effector T(H)1 and T(H)2 cells are controlled by specialized subsets of regulatory T cells. Some pathogens can induce regulatory cells to evade immune elimination, but regulatory pathways are homeostatic and mainly triggered by harmless microorganisms. Helminths, saprophytic mycobacteria, bifidobacteria and lactobacilli, which induce immunoregulatory mechanisms in the host, ameliorate aberrant immune responses in the setting of allergy and inflammatory bowel disease. These organisms cause little, if any, harm, and have been part of human microecology for millennia; however, they are now less frequent or even absent in the human environment of westernized societies. Deficient exposure to these 'old friends' might explain the increase in immunodysregulatory disorders. The use of probiotics, prebiotics, helminths or microbe-derived immunoregulatory vaccines might, therefore, become a valuable approach to disease prevention.

The anti-inflammatory mechanisms of Hsp70

Immune responses to heat shock proteins (Hsp) develop in virtually all inflammatory diseases; however, the significance of such responses is only now becoming clear. In experimental disease models, Hsp administration can prevent or arrest inflammatory damage, and in initial clinical trials in patients with chronic inflammatory diseases, Hsp peptides have been shown to promote the production of anti-inflammatory cytokines, indicating immunoregulatory potential of Hsp. Therefore, the presence of immune responses to Hsp in inflammatory diseases can be seen as an attempt of the immune system to correct the inflammatory condition. Hsp70 can modulate inflammatory responses in models of arthritis, colitis and graft rejection, and the mechanisms underlying this effect are now being elucidated. Incubation with microbial Hsp70 was seen to induce tolerogenic dendritic cells (DCs) and to promote a suppressive phenotype in myeloid-derived suppressor cells and monocytes. These DC could induce regulatory T cells (Tregs), independently of the antigens they presented. Some Hsp70 family members are associated with autophagy, leading to a preferential uploading of Hsp70 peptides in MHC class II molecules of stressed cells. Henceforth, conserved Hsp70 peptides may be presented in these situations and constitute targets of Tregs, contributing to downregulation of inflammation. Finally, an interfering effect in multiple intracellular inflammatory signaling pathways is also known for Hsp70. Altogether it seems attractive to use Hsp70, or its derivative peptides, for modulation of inflammation. This is a physiological immunotherapy approach, without the immediate necessity of defining disease-specific auto-antigens. In this article, we present the evidence on anti-inflammatory effects of Hsp70 and discuss the need for experiments that will be crucial for the further exploration of the immunosuppressive potential of this protein.

Caught with their PAMPs down? The extracellular signalling actions of molecular chaperones are not due to microbial contaminants

In recent years, it has been hypothesised that a new signalling system may exist in vertebrates in which secreted molecular chaperones form a dynamic continuum between the cellular stress response and corresponding homeostatic physiological mechanisms. This hypothesis seems to be supported by the finding that many molecular chaperones are released from cells and act as extracellular signals for a range of cells. However, this nascent field of biological research seems to suffer from an excessive criticism that the biological activities of molecular chaperones are due to undefined components of the microbial expression hosts used to generate recombinant versions of these proteins. In this article, a number of the proponents of the cell signalling actions of molecular chaperones take this criticism head-on. They show that sufficient evidence exists to support fully the hypothesis that molecular chaperones have cell-cell signalling actions that are likely to be part of the homeostatic mechanism of the vertebrate.

Progressive bovine paratuberculosis is associated with local loss of CD4(+) T cells, increased frequency of gamma delta T cells, and related changes in T-cell function

Bovine paratuberculosis is caused by the infection of young calves with Mycobacterium avium subsp. paratuberculosis, resulting in a chronic granulomatous infection of predominantly the ileum. After an incubation period of 2 to 5 years, the disease becomes progressive in some of the chronically infected, but asymptomatic cows. This results in a protein-losing enteropathy that will ultimately be fatal. A loss of cell-mediated immune responses in symptomatic animals has been described, but no information is available concerning immune reactivity in the intestine. We sought to investigate putative disease status-associated lymphocyte subset distributions and antigen-specific functional characteristics of mononuclear cells isolated from blood, gut-associated lymphoid tissue, and the intestinal walls of 22 cows in different stages of disease and in control animals. The results demonstrated a significant decrease in CD4(+) T-cell frequency and a significant increase in TcR1-N12(+) gamma delta T-cell frequency in ileum lamina propria lymphocytes of symptomatic animals compared to the asymptomatic shedders. Immunohistology revealed that there was also an absolute decrease in the number of CD4(+) T cells in sections of the lesional ileum. Our findings also indicated that both peripheral and intestinal cell-mediated responses are decreased in symptomatic animals compared to asymptomatic animals. We conclude that the decrease in cell-mediated responses is likely related to a loss of antigen-specific CD4(+) T cells, which is most prominent in the lesional ileum from symptomatic animals, thus contributing to the progressive nature of bovine paratuberculosis.

A case of mistaken identity: HSPs are no DAMPs but DAMPERs

Until recently, the immune system was seen solely as a defense system with its primary task being the elimination of unwanted microbial invaders. Currently, however, the functional significance of the immune system has obtained a much wider perspective, to include among others the maintenance and restoration of homeostasis following tissue damage. In this latter aspect, there is a growing interest in the identification of molecules involved, such as the so-called danger or damage-associated molecular patterns (DAMPs), also called alarmins. Since heat shock proteins are archetypical molecules produced under stressful conditions, such as tissue damage or inflammation, they are frequently mentioned as prime examples of DAMPs (Bianchi, J Leukoc Biol 81:1-5, 2007; Kono and Rock, Nat Rev Immunol 8:279-289, 2008; Martin-Murphy et al., Toxicol Lett 192:387-394, 2010). See for instance also a recent review (Chen and Nunez, Science 298:1395-1401, 2010). Contrary to this description, we recently presented some of the arguments against a role of heat shock protein as DAMPs (Broere et al., Nat Rev Immunol 11:565-c1, 2011). With this perspective and reflection article, we hope to elaborate on this debate and provide additional thoughts to further ignite this discussion on this critical and evolving issue.

Mycobacterial 70 kD heat-shock protein is an effective subunit vaccine against bovine paratuberculosis

Paratuberculosis is a chronic granulomatous inflammation of the small intestine of cattle and other ruminants, caused by infection with Mycobacterium avium ssp. paratuberculosis (MAP). The disease can be found in ruminant herds worldwide, causing substantial economic losses at farm level due to premature culling and production losses. In previous studies, it has been shown that immune responses to recombinant MAP Hsp70 proteins were predominantly cell mediated. As protective immunity to the intracellular mycobacterial pathogens is thought to be cell-mediated in origin, we have studied the use of a recombinant MAP Hsp70 as a subunit vaccine in cattle experimentally infected with MAP. The results of the current study demonstrate that recombinant MAP Hsp70 can be successfully used as a subunit vaccine against bovine paratuberculosis, significantly reducing shedding of bacteria in feces during the first 2 years following experimental infection.

Cell stress induced HSP are targets of regulatory T cells: A role for HSP inducing compounds as anti-inflammatory immuno-modulators?

T cell responses to heat shock proteins (HSP) have disease suppressive activities through production of anti-inflammatory cytokines in patients and in models of inflammatory diseases. There is evidence that the anti-inflammatory activity of HSP-specific T cells depends on their recognition of endogenous HSP epitopes as expressed by stressed cells at sites of inflammation. Previously, we have demonstrated that such T cells can be induced by conserved sequences of microbial HSP. Now we propose that drug induced up-regulation of endogenous HSP can contribute to anti-inflammatory T cell regulation.

Immunopotentiating heat shock proteins: negotiators between innate danger and control of autoimmunity

Heat shock proteins (hsps) are known to be immunodominant antigens of bacteria. Hsps are evolutionarily strongly conserved proteins present in all eukaryotic and prokaryotic cellular organisms and upregulated by several forms of stress. Despite (the paradigm of) self-tolerance, hsp-epitopes homologous to endogenous host hsp sequences have been implicated as T cell epitopes to endow crossreactive, hsp-specific T cells with the capacity to regulate inflammation, such as in experimentally induced autoimmune diseases. Such T cells were found to produce regulatory cytokines like IL10, in contrast to T cells induced with other conserved microbial proteins that are not upregulated by stress. Hsps have been implicated in immune regulation not only as upregulated targets of adaptive immunity during inflammatory stress, but recently also as triggering factors for innate immunity through activation via Toll-like receptors (TLRs).

A novel heat-shock protein coinducer boosts stress protein Hsp70 to activate T cell regulation of inflammation in autoimmune arthritis

OBJECTIVE

Stress proteins, such as members of the heat-shock protein (HSP) family, are up-regulated by cells in inflamed tissue and can be viewed functionally as "biomarkers" for the immune system to monitor inflammation. Exogenous administration of stress proteins has induced immunoregulation in various models of inflammation and has also been shown to be effective in clinical trials in humans. This study was undertaken to test the hypothesis that boosting of endogenous HSP expression can restore effective immunoregulation through T cells specific for stress proteins.

METHODS

Stress protein expression was manipulated in vivo and in vitro with a food component (carvacrol), and immune recognition of stress proteins was studied.

RESULTS

Carvacrol, a major compound in the oil of many Origanum species, had a notable capacity to coinduce cellular Hsp70 expression in vitro and, upon intragastric administration, in Peyer's patches of mice in vivo. As a consequence, carvacrol specifically promoted T cell recognition of endogenous Hsp70, as demonstrated in vitro by the activation of an Hsp70-specific T cell hybridoma and in vivo by amplified T cell responses to Hsp70. Carvacrol administration also increased the number of CD4+CD25+FoxP3+ T cells, systemically in the spleen and locally in the joint, and almost completely suppressed proteoglycan-induced experimental arthritis. Furthermore, protection against arthritis could be transferred with T cells isolated from carvacrol-fed mice.

CONCLUSION

These findings illustrate that a food component can boost protective T cell responses to a self stress protein and down-regulate inflammatory disease, i.e., that the immune system can respond to diet.

The bovine CD1 family contains group 1 CD1 proteins, but no functional CD1d

The CD1 family of proteins presents lipid Ags to T cells. Human CD1a, CD1b, and CD1c have been shown in humans to present mycobacterial lipid Ags. Cattle, like humans, are a natural host of several mycobacterial pathogens. In this study, we describe the CD1 family of genes in cattle (Bos taurus) and provide evidence that B. taurus expresses CD1a, CD1e, and multiple CD1b molecules, but no CD1c and CD1d molecules. In mice and humans, CD1d is known to present Ag to NKT cells, a T cell lineage that is characterized by a limited TCR repertoire, capable of rapidly secreting large amounts of IFN-gamma and IL-4. In cattle, two CD1D pseudogenes were found and no intact CD1D genes. Consistent with this, we found complete lack of reactivity to a potent, cross-reactive Ag for NKT cells in mice and humans, alpha-galactosylceramide. Our data suggest the absence of NKT cells in cattle. It remains open whether other cells with the NKT-like phenotype and functions are present in this species. With its functional CD1A and CD1B genes, B. taurus is well equipped to present Ags to CD1-restricted T cells other than NKT cells. Cattle can be used as a model to study group 1 CD1-restricted T cell immunity, including its role in the defense against mycobacterial infections that occur naturally in this species.

The Enigma of Heat Shock Proteins in Immune Tolerance

The fundamental problem of autoimmune diseases is the failure of the immune system to downregulate its own potentially dangerous cells, which leads to destruction of tissue expressing the relevant autoantigens. Current immunosuppressive therapies offer relief but fail to restore the basic condition of self-tolerance. They do not induce long-term physiological regulation resulting in medication-free disease remissions. Heat shock proteins (HSPs) have shown to possess the capacity of inducing lasting protective immune responses in models of experimental autoimmune diseases. Especially mycobacterial HSP60 and HSP70 were shown to induce disease inhibitory IL-10-producing regulatory T cells in many different models. This in itself may seem enigmatic, since based on earlier studies, HSPs were also coined sometimes as pro-inflammatory damage-associated molecular patterns. First clinical trials with HSPs in rheumatoid arthritis and type I diabetes have also indicated their potential to restore tolerance in autoimmune diseases. Data obtained from the models have suggested three aspects of HSP as being critical for this tolerance promoting potential: 1. evolutionary conservation, 2. most frequent cytosolic/nuclear MHC class II natural ligand source, and 3. upregulation under (inflammatory) stress. The combination of these three aspects, which are each relatively unique for HSP, may provide an explanation for the enigmatic immune tolerance promoting potential of HSP.

Inhibition of adjuvant-induced arthritis by interleukin-10-driven regulatory cells induced via nasal administration of a peptide analog of an arthritis-related heat-shock protein 60 T cell epitope

OBJECTIVE

To prevent and treat experimental arthritis via nasal administration of an altered peptide ligand (APL) from the major arthritogenic epitope in adjuvant-induced arthritis (AIA) and to explore the mechanisms involved.

METHODS

Peptides were administered nasally before and after induction of arthritis. Splenocytes and lymph node cells draining both the site of inflammation and the site of tolerance induction were used for cell transfer and were studied for antigen-specific T cell characteristics. In addition, attempts were made to stop T cell tolerance in vitro, using anticytokine antibodies.

RESULTS

Nasal administration of a modulatory APL of the heat-shock protein 60 (Hsp60) 180-188 T cell epitope, alanine 183, had a suppressive effect in AIA that far exceeded that of the wild-type epitope. In addition to its effectiveness in preventing AIA, alanine 183 may be effective in the treatment of ongoing AIA. The protective effect of alanine 183 can be passively transferred using activated splenocytes. Nasal administration of alanine 183 did not lead to detectable T cell proliferation or interleukin-2 (IL-2) production in mandibular lymph node cells, while transforming growth factor beta (TGF beta), IL-10, and IL-4 were readily produced. Likewise, after nasally induced tolerance, followed by induction of arthritis, inguinal lymph node cells produced IL-4, TGF beta, and IL-10. After neutralizing in vitro the individual cytokines with anticytokine antibodies, only blocking of IL-10 production led to reversal of tolerance, at the site of tolerance induction and the site of inflammation.

CONCLUSION

Nasal administration of an APL of Hsp60 180-188 induces highly effective protection against AIA through generation of regulatory cells that produce IL-4, TGF beta, and IL-10, whereas the induced tolerance is driven mainly by production of IL-10.

Ligand-induced differential cross-regulation of Toll-like receptors 2, 4 and 5 in intestinal epithelial cells

Toll-like receptors (TLR) 2, TLR4 and TLR5 are primary mucosal sensors of microbial patterns. Dissection of the cross-talk between TLRs in intestinal cells has thus far been hampered by the lack of functional TLR2 and TLR4 in in vitro model systems. Here we report that the mouse intestinal epithelial cell line mIC(cl2) expresses these TLRs and that receptor expression and function are regulated by environmental TLR stimuli. Our results show that stimulation of TLR5 by bacterial flagellin resulted in upregulated TLR2 and TLR4 mRNA and concomitant sensitization of the cells for subsequent TLR2 (Pam(3)CSK(4)) and TLR4 (LPS) stimulation. Exposure to low amounts of either Pam(3)CSK(4) or LPS in turn downregulated TLR5 mRNA and attenuated subsequent flagellin-mediated NF-kappaB activation, pointing to a negative feedback mechanism. Pam(3)CSK(4) and LPS also downregulated TLR4 mRNA but upregulated TLR2 mRNA and sensitized cells for subsequent TLR2 stimulation. Inhibition of the phosphatidyl-inositol-3-kinase/Akt pathway only affected LPS-mediated TLR cross-talk indicating that differential TLR cross-regulation was conferred via different mechanisms. Together, our results demonstrate that the expression and function of TLR in intestinal cells are highly dynamic and tightly regulated in response to encountered bacterial stimuli.

IL-10 is critically involved in mycobacterial HSP70 induced suppression of proteoglycan-induced arthritis

Background

The anti-inflammatory capacity of heat shock proteins (HSP) has been demonstrated in various animal models of inflammatory diseases and in patients. However, the mechanisms underlying this anti-inflammatory capacity are poorly understood. Therefore, the possible protective potential of HSP70 and its mechanisms were studied in proteoglycan (PG) induced arthritis (PGIA), a chronic and relapsing, T cell mediated murine model of arthritis.

Methodology/Principal Findings

HSP70 immunization, 10 days prior to disease induction with PG, inhibited arthritis both clinically and histologically. In addition, it significantly reduced PG-specific IgG2a but not IgG1 antibody production. Furthermore, IFN-γ and IL-10 production upon in vitro restimulation with HSP70 was indicative of the induction of an HSP70-specific T cell response in HSP70 immunized mice. Remarkably, HSP70 treatment also modulated the PG-specific T cell response, as shown by the increased production of IL-10 and IFN-γ upon in vitro PG restimulation. Moreover, it increased IL-10 mRNA expression in CD4⁺CD25⁺ cells. HSP70 vaccination did not suppress arthritis in IL-10^−/− mice, indicating the crucial role of IL-10 in the protective effect.

Conclusions/Significance

In conclusion, a single mycobacterial HSP70 immunization can suppress inflammation and tissue damage in PGIA and results in an enhanced regulatory response as shown by the antigen-specific IL-10 production. Moreover, HSP70 induced protection is critically IL-10 dependent.

Identification of new populations of chicken natural killer (NK) cells

Natural killer (NK) cell activity is conserved throughout vertebrate development, but characterization of non-mammalian NK-cells has been hampered by the absence of specific mAbs for these cells. Monoclonal antibodies were generated against in vitro IL-2 expanded sorted CD3-CD8alpha+ peripheral blood lymphocytes, previously described to contain chicken NK-cells. Screening of embryonic and adult splenocytes with hybridoma supernatants resulted in five candidate NK markers. Activation of chicken NK-cells with PMA/Ionomycin or with the NK target cell-line LSCC-RP9 resulted in increased expression of CD107 (LAMP-1) and a newly developed flow cytometry based cytotoxicity assay showed that NK-cells were able to kill target cells. Combining NK markers with functional assays indicated that marker positive cells showed NK-cell function. In conclusion, we generated new monoclonal antibodies and developed two functional assays which will enhance our understanding of the role of NK-cells in healthy and diseased chickens.

Heat shock protein 60 and adjuvant arthritis: a model for T cell regulation in human arthritis

Heat shock proteins (hsp) are highly conserved, immune-dominant microbial proteins, whose expression is increased at sites of inflammation. In the experimental model of adjuvant arthritis (AA) immune responses to hsp determine the outcome of disease. AA can be transferred with a single T cell clone specific for a sequence of mycobacterial hsp65 (Mhsp65). Immunization with whole Mhsp65 on the other hand, protects in virtually all forms of experimental arthritis, including AA. This protective effect seems the consequence of the induction of a T cell response directed against self-hsp60. A similar protective effect of self-hsp60-specific T cells seems present in patients with a spontaneous remitting form of juvenile idiopathic arthritis. Next to hsp60, other hsp have similar protective effects in arthritis, while other conserved microbial proteins lack such capacity. Nasal administration of hsp60 peptides induces IL-10-driven regulatory T cells that are highly effective in suppressing arthritis. Thus hsp60, or peptides derived from hsp60, are suitable candidates for immune therapy in chronic arthritis.

Early host responses to avian influenza A virus are prolonged and enhanced at transcriptional level depending on maturation of the immune system

Newly hatched chickens are more susceptible to infectious diseases than older birds because of an immature immune system. The aim of this study was to determine to what extent host responses to avian influenza virus (AIV) inoculation are affected by age. Therefore, 1- and 4-week (wk) old birds were inoculated with H9N2 AIV or saline. The trachea and lung were sampled at 0, 8, 16 and 24h post-inoculation (h.p.i.) and gene expression profiles determined using microarray analysis. Firstly, saline controls of both groups were compared to analyse the changes in gene profiles related to development. In 1-wk-old birds, higher expression of genes related to development of the respiratory immune system and innate responses were found, whereas in 4-wk-old birds genes were up regulated that relate to the presence of higher numbers of leukocytes in the respiratory tract. After inoculation with H9N2, gene expression was most affected at 16 h.p.i. in 1-wk-old birds and at 16 and 24h.p.i. in 4-wk-old birds in the trachea and especially in the lung. In 1-wk-old birds less immune related genes including innate related genes were induced which might be due to age-dependent reduced functionality of antigen presenting cells (APC), T cells and NK cells. In contrast cytokine and chemokines gene expression was related to viral load in 1-wk-old birds and less in 4-wk-old birds. Expression of cellular host factors that block virus replication by interacting with viral factors was independent of age or tissue for most host factors. These data show that differences in development are reflected in gene expression and suggest that the strength of host responses at transcriptional level may be a key factor in age-dependent susceptibility to infection, and the cellular host factors involved in virus replication are not.

Functional CD1d and/or NKT cell invariant chain transcript in horse, pig, African elephant and guinea pig, but not in ruminants

CD1d-restricted invariant natural killer T cells (NKT cells) have been well characterized in humans and mice, but it is unknown whether they are present in other species. Here we describe the invariant TCR alpha chain and the full length CD1d transcript of pig and horse. Molecular modeling predicts that porcine (po) invariant TCR alpha chain/poCD1d/alpha-GalCer and equine (eq) invariant TCR alpha chain/eqCD1d/alpha-GalCer form complexes that are highly homologous to the human complex. Since a prerequisite for the presence of NKT cells is the expression of CD1d protein, we performed searches for CD1D genes and CD1d transcripts in multiple species. Previously, cattle and guinea pig have been suggested to lack CD1D genes. The CD1D genes of European taurine cattle (Bos taurus) are known to be pseudogenes because of disrupting mutations in the start codon and in the donor splice site of the first intron. Here we show that the same mutations are found in six other ruminants: African buffalo, sheep, bushbuck, bongo, N'Dama cattle, and roe deer. In contrast, intact CD1d transcripts were found in guinea pig, African elephant, horse, rabbit, and pig. Despite the discovery of a highly homologous NKT/CD1d system in pig and horse, our data suggest that functional CD1D and CD1d-restricted NKT cells are not universally present in mammals.

DEC205+ Dendritic Cell-Targeted Tolerogenic Vaccination Promotes Immune Tolerance in Experimental Autoimmune Arthritis

Previous studies in mouse models of autoimmune diabetes and encephalomyelitis have indicated that the selective delivery of self-antigen to the endocytic receptor DEC205 on steady-state dendritic cells (DCs) may represent a suitable approach to induce Ag-specific immune tolerance. In this study, we aimed to examine whether DEC205(+) DC targeting of a single immunodominant peptide derived from human cartilage proteoglycan (PG) can promote immune tolerance in PG-induced arthritis (PGIA). Besides disease induction by immunization with whole PG protein with a high degree of antigenic complexity, PGIA substantially differs from previously studied autoimmune models not only in the target tissue of autoimmune destruction but also in the nature of pathogenic immune effector cells. Our results show that DEC205(+) DC targeting of the PG peptide 70-84 is sufficient to efficiently protect against PGIA development. Complementary mechanistic studies support a model in which DEC205(+) DC targeting leads to insufficient germinal center B cell support by PG-specific follicular helper T cells. Consequently, impaired germinal center formation results in lower Ab titers, severely compromising the development of PGIA. Overall, this study further corroborates the potential of prospective tolerogenic DEC205(+) DC vaccination to interfere with autoimmune diseases, such as rheumatoid arthritis.