Induction of IL-10 and inhibition of experimental arthritis are specific features of microbial heat shock proteins that are absent for other evolutionarily conserved immunodominant proteins

Bacterial heat shock proteins (hsp) are evolutionary conserved immunodominant proteins that manifest amino acid homologies with hsp present in mammalian cells. Preimmunization with mycobacterial hsp65 has been found to protect against various forms of experimental arthritis. As these protective effects have previously been attributed to induction of self homologue cross-reactive T cell responses, the question was raised as to whether this protective effect could be extended to other highly conserved and immunodominant microbial Ags with mammalian homologues. Therefore, we immunized Lewis rats with conserved bacterial Ags (superoxide dismutase, aldolase, GAPDH, and hsp70). Although all Ags appeared highly immunogenic, we only found a protective effect in experimental arthritis after immunization with bacterial hsp70. The protective effect of hsp70 was accompanied with a switch in the subclasses of hsp70-specific Abs, suggesting the induction of Th2-like response. The most striking difference between immunization with hsp70 and all other immunodominant Ags was the expression of IL-10 found after immunization with hsp70. Even more, while immunization with hsp70 led to Ag-induced production of IL-10 and IL-4, immunization with aldolase led to increased production of IFN-gamma and TNF-alpha. Thus, the protective effect of conserved immunodominant proteins in experimental arthritis seems to be a specific feature of hsp. Therefore, hsp may offer unique possibilities for immunological intervention in inflammatory diseases.

Arthritis protective regulatory potential of self-heat shock protein cross-reactive T cells

Immunization with heat shock proteins has protective effects in models of induced arthritis. Analysis has shown a reduced synovial inflammation in such protected animals. Adoptive transfer and immunization with selected T cell epitopes (synthetic peptides) have indicated the protection to be mediated by T cells directed to conserved hsp epitopes. This was shown first for mycobacterial hsp60 and later for mycobacterial hsp70. Fine specificity analysis showed that such T cells were cross-reactive with the homologous self hsp. Therefore protection by microbial hsp reactive T cells can be by cross-recognition of self hsp overexpressed in the inflamed tissue. Preimmunization with hsp leads to a relative expansion of such self hsp cross-responsive T cells. The regulatory nature of such T cells may originate from mucosal tolerance maintained by commensal flora derived hsp or from partial activation through recognition of self hsp as a partial agonist (Altered Peptide Ligand) or in the absence of proper costimulation. Recently, we reported the selective upregulation of B7.2 on microbial hsp600 specific T cells in response to self hsp60. Through a preferred interaction with CTLA-4 on proinflammatory T cells this may constitute an effector mechanism of regulation. Also, regulatory T cells produced IL10.

Polyspecific immunoglobulins (IVIg) suppress proliferation of human (auto)antigen-specific T cells without inducing apoptosis

Polyspecific immunoglobulins (IVIg) have been shown to reduce disease activity in multiple sclerosis (MS). To investigate the mechanisms of action of IVIg, we studied the impact of IVIg on growth and death (apoptosis) of human (auto)antigen-specific T cells. We observed a substantial suppression of proliferation of specifically activated T cells, in absence of caspase activation or DNA fragmentation. Further, neither susceptibility of T cells to undergo CD95-mediated apoptosis nor expression of apoptosis-blocking bcl-2 was modulated by IVIg. We conclude that IVIg may inhibit the reactivity of antigen-specific T cells in MS through suppression of proliferation rather than modulation of apoptosis.

Arthritis protective regulatory potential of self-heat shock protein cross-reactive T cells

Immunization with heat shock proteins has protective effects in models of induced arthritis. Analysis has shown a reduced synovial inflammation in such protected animals. Adoptive transfer and immunization with selected T cell epitopes (synthetic peptides) have indicated the protection to be mediated by T cells directed to conserved hsp epitopes. This was shown first for mycobacterial hsp60 and later for mycobacterial hsp70. Fine specificity analysis showed that such T cells were cross-reactive with the homologous self hsp. Therefore protection by microbial hsp reactive T cells can be by cross-recognition of self hsp overexpressed in the inflamed tissue. Preimmunization with hsp leads to a relative expansion of such self hsp cross-responsive T cells. The regulatory nature of such T cells may originate from mucosal tolerance maintained by commensal flora derived hsp or from partial activation through recognition of self hsp as a partial agonist (Altered Peptide Ligand) or in the absence of proper costimulation. Recently, we reported the selective upregulation of B7.2 on microbial hsp600 specific T cells in response to self hsp60. Through a preferred interaction with CTLA-4 on proinflammatory T cells this may constitute an effector mechanism of regulation. Also, regulatory T cells produced IL10.

Dual effect of glucocorticoids on apoptosis of human autoreactive and foreign antigen-specific T cells

The efficacy of glucocorticoids in the treatment of multiple sclerosis may involve the induction of T cell apoptosis. Here, we report that glucocorticoids have two different effects on the vulnerability of human antigen-specific T cells: (i) steroids induce T cell apoptosis in a CD95-independent, but caspase-dependent manner; (ii) steroids protect T cells from CD95-mediated apoptosis which, however, is also caspase-dependent. An increase in BCL-2 expression is observed upon incubation with steroids. Thus, inhibition of CD95-mediated T cell apoptosis may be an undesirable side-effect resulting in survival of activated T cells and the maintenance of pathogenic immune responses might explain the lack of long-term glucocorticoid therapy.

[Apoptosis in multiple sclerosis. Etiopathogenetic relevance and prospects for new therapeutic strategies]

Apoptosis, or programmed cell death, is a physiological cell suicide program mainly leading to selective elimination of useless cells. This mechanism is important for the homeostasis of the immune system and presumably plays a two-sided role in the pathogenesis of multiple sclerosis (MS). On the one hand, evidence has been provided that impaired apoptosis might result in increased numbers or persistence of activated myelin-specific T cells, thus inducing the pathophysiologic processes in MS. On the other hand, local tissue damage might involve apoptosis of glial and neuronal cells and lead to the clinical symptoms. Here, an overview is presented on the current knowledge of the role of apoptosis in the pathogenesis of MS, and implications for related therapeutic strategies are discussed.

Human brain-cell death induced by tumour-necrosis-factor-related apoptosis-inducing ligand (TRAIL)

Cell death induced by tumour-necrosis-factor-related apoptosis-inducing ligand (TRAIL) was believed to occur exclusively in tumour cells, suggesting that this drug is safe to use as an antitumour therapy. Concerns were raised, however, when cultured normal human hepatocytes were shown to be susceptible to TRAIL. Here we report that TRAIL induces apoptosis in the human brain. Our finding therefore argues against the use of TRAIL for therapy of human brain tumours. However, neuroinflammatory T cells that express TRAIL might induce apoptosis of brain tissue, indicating a potential target for treatment of multiple sclerosis.

Expression of TRAIL receptors in human autoreactive and foreign antigen-specific T cells

Deletion of T cells due to apoptosis induction is a regulatory mechanism in the human immune system that may be impaired in autoimmune diseases such as multiple sclerosis (MS). Involvement of the apoptosis-mediating CD95/CD95 ligand system in MS has been demonstrated. Here, we report that (auto)antigen-specific human T cells are not killed in vitro by soluble TNF-related apoptosis-inducing ligand (TRAIL) although expressing death-inducing receptors, TRAIL receptor 1 (TRAIL-R1) and TRAIL-R2. Apoptosis was assessed by caspase activation and DNA fragmentation, receptor expression was detected by RT - PCR and flow cytometry. The (auto)antigen-specific T cells were also resistant to specific TRAIL-R1/TRAIL-R2-directed induction of apoptosis, indicating that coexpression of the truncated TRAIL-R3 and TRAIL-R4 in these T cells is not responsible for the observed resistance. Upon stimulation, levels of death-inducing TRAIL receptors decreased whereas TRAIL was up-regulated on the cell surface. In contrast to CD95, the role of TRAIL receptors in MS might not involve regulation of T cell vulnerability.

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

Immunization with Mycobacterium tuberculosis heat shock protein (hsp) 60 has been shown to protect rats from experimental arthritis. Previously, the protection-inducing capacity was shown to reside in the evolutionary conserved parts of the molecule. Now we have studied the nature of the arthritis suppressive capacity of a distinct, antigenically unrelated protein, M. tuberculosis hsp70. Again, a conserved mycobacterial hsp70 sequence was found to be immunogenic and to induce T cells that cross-reacted with the rat homologue sequence. However, in this case parenteral immunization with the peptide containing the critical cross-reactive T cell epitope did not suppress disease. Upon analysis of cytokines produced by these peptide-specific T cells, high IL-10 production was found, as was the case with T cells responsive to whole hsp70 protein. Nasal administration of this peptide was found to lead to inhibition of subsequent adjuvant arthritis induction. The data presented here shows the intrinsic capacity of conserved bacterial hsp to trigger self-hsp cross-reactive T cells with the potential to down-regulate arthritis via IL-10.

Partial synergy of bisindolylmaleimide with apoptotic stimulus in antigen-specific T cells--implications for multiple sclerosis

In multiple sclerosis (MS), induction of T cell apoptosis constitutes a promising therapeutic strategy. Recently, bisindolylmaleimide has been shown to be an effective treatment of experimental autoimmune encephalomyelitis, presumably due to enhancement of CD95-mediated T cell apoptosis. Therefore, we studied the effects of bisindolylmaleimide on human (auto)antigen-specific T cells. We observed a synergistic effect of bisindolylmaleimide with apoptotic stimulus assessed via caspase activity and annexin V-binding, but no potentiation of DNA fragmentation or cell death. Thus, bisindolylmaleimide might be useful for modulating T cell apoptosis, yet more potent substances have to be generated re-establishing immunological control over auto-reactive T cells.

Oral administration of HSP-containing E. coli extract OM-89 has suppressive effects in autoimmunity. Regulation of autoimmune processes by modulating peripheral immunity towards hsp's?

OM-89 (Subreum) is an E. coli extract used for oral administration in the treatment of rheumatoid arthritis. It contains bacterial heat shock proteins, namely hsp60 and hsp70, which were shown to be major immunogenic constituents of the drug. Immunity to bacterial heat-shock antigens was shown to be a means of immunomodulation of (experimental) autoimmune disease and possibly inflammation in general. This was demonstrated for mycobacterial hsp60 respectively hsp70 in autoimmune disease models for arthritis, diabetes and encephalitis. Parallel to the effects displayed by immunisation with hsp, oral administration of hsp-containing OM-89 was found to modify autoimmune disease in a number of animal models, such as for arthritis, diabetes and SLE. In rats immunisation with OM-89 was found to lead to proliferative T cell responses to hsp60 and hsp70 of both E. coli and mycobacterial origin. Conversely, immunisation with hsp antigens could induce T cell reactivity specific for OM-89. Given this and the autoimmune disease modulating properties of both hsp and OM-89 it is argued that OM-89 acts via the same mechanism as proposed for hsp: that peripheral tolerance is induced at the level of regulatory T cells with specificity for heat-shock proteins. This may constitute one mode of action for OM-89 as an arthritis suppressive oral drug in man.

Antirheumatic E. coli extract OM-89 induces T cell responses to HSP60 and 70

Oral administration of E. coli extract OM-89 is used in treating RA. It has been shown that immune reactivity to heat-shock proteins (hsp) is involved in immunomodulation of arthritis. We evaluated the postulated presence and immunogenicity of hsp's in OM-89. The effects of OM-89 in experimental arthritis were analyzed. Proliferative T cell responses to bacterial hsp60 and hsp70 were found in rats immunized with OM-89. And conversely, immunization with hsp antigens induced OM-89-specific T cell responses. Hsp70 (DnaK) was found to be a major immunogenic constituent of OM-89. Parenteral immunization with OM-89 reduces resistance to adjuvant arthritis (AA), whereas oral administration protects against AA. Given the arthritis inhibitory effect of oral OM-89 in AA our findings suggest peripheral tolerance induced by hsp-specific regulatory T cells as a mode of action for OM-89 as an arthritis suppressive oral drug.

Full length cDNA of rat RT1.DMa and RT1.DMb and expression of RT1.DM genes in dendritic and Langerhans cells

MHC encoded DM heterodimers and classical MHC class II complexes meet in an endosomal/lysosomal compartment where DM heterodimers support peptide loading of MHC class II. Studies on peptide loading of rat class II and on peptide persistence in cells of the dendritic lineage prompted us to establish full length cDNA clones coding for the subunits alpha and beta of rat DM molecules as well as a mAb directed against the luminal moiety of the beta subunit. Here we describe the establishment of the first full length cDNA clones of rat RT1.DMa and RT1.DMb. The mode of expression of RT1.DM at the transcript level in bone marrow culture-derived dendritic cells, in Langerhans cells and in a number of additional accessory cells is reported. The beta protein was identified in detergent lysates of RT1.DM expressing cells by Western blot analysis using a newly established monoclonal antibody directed against the luminal part of RT1.DMbeta.

An MHC class II-expressing T cell clone presenting conventional antigen lacks the ability to present bacterial superantigen

We have analyzed the response of rat T cells to myelin basic protein (MBP) and the bacterial superantigen, staphylococcal enterotoxin E (SEE). Rat T cells reactive with MBP can respond to SEE presented by spleen cells but not to SEE presented by LOA, a rat T cell clone that expresses both I-A and I-E MHC class II molecules, even though LOA is much more efficient than splenic APC in the presentation of MBP. The inability of LOA to present superantigen is not due to a structural difference in MHC II molecules between LOA and the splenic APC or to differential expression of major accessory/adhesion molecules, including CD2, CD5, CD4 and CD44, on LOA. The non-responsiveness of SEE/LOA-induced T cells differs from anergy, in that such cells do not lose their subsequent responsiveness to either MBP or SEE. Our results demonstrate that: (i) MHC class II molecules (I-A and I-E) alone are insufficient for the activation of T cells by bacterial superantigen, (ii) failure to respond to antigen presented upon inappropriate APC or in inadequate doses may not necessarily represent anergy, and (iii) the quality of the T cell response towards certain ligands can be strongly influenced by the nature of the APC.

Complete coding nucleotide sequence of cDNA for the class II RT1.B beta I chain of the Lewis rat

We have established the first full length cDNA clone for the beta light chain of the MHC class II alpha, beta heterodimer (isotype RT1.B) of the rat. Clone pLR beta 118 was obtained from a self-primed lambda gt10 cDNA library of IFN-tau treated bone marrow-derived macrophages of the Lewis rat. Subcloning of pLR beta 118 into a transcription vector with subsequent in vitro transcription and translation using the reticulocyte lysate system in the presence of microsomes followed by immunoprecipitation with mAb OX6 and two-dimensional gel electrophoresis revealed the intact RT1.B beta I-chain.