The role of the MHC class II transactivator in class II expression and antigen presentation by astrocytes and in susceptibility to central nervous system autoimmune disease

Mycobacterium bovis bacillus Calmette-Guérin secreting active cathepsin S stimulates expression of mature MHC class II molecules and antigen presentation in human macrophages

A successful Th cell response to bacterial infections is induced by mature MHC class II molecules presenting specific Ag peptides on the surface of macrophages. In recent studies, we demonstrated that infection with the conventional vaccine Mycobacterium bovis bacillus Calmette-Guérin (BCG) specifically blocks the surface export of mature class II molecules in human macrophages by a mechanism dependent on inhibition of cathepsin S (Cat S) expression. The present study examined class II expression in macrophages infected with a rBCG strain engineered to express and secrete biologically active human Cat S (rBCG-hcs). Cat S activity was completely restored in cells ingesting rBCG-hcs, which secreted substantial levels of Cat S intracellularly. Thus, infection with rBCG-hcs, but not parental BCG, restored surface expression of mature MHC class II molecules in response to IFN-gamma, presumably as result of MHC class II invariant chain degradation dependent on active Cat S secreted by the bacterium. These events correlated with increased class II-directed presentation of mycobacterial Ag85B to a specific CD4(+) T cell hybridoma by rBCG-hcs-infected macrophages. Consistent with these findings, rBCG-hcs was found to accelerate the fusion of its phagosome with lysosomes, a process that optimizes Ag processing in infected macrophages. These data demonstrated that intracellular restoration of Cat S activity improves the capacity of BCG-infected macrophages to stimulate CD4(+) Th cells. Given that Th cells play a major role in protection against tuberculosis, rBCG-hcs would be a valuable tuberculosis vaccine candidate.

CD11b+Ly-6C(hi) suppressive monocytes in experimental autoimmune encephalomyelitis

Innate immune cells may regulate adaptive immunity by balancing different lineages of T cells and providing negative costimulation. In addition, CD11b(+)Gr-1(+) myeloid-derived suppressor cells have been described in tumor, parasite infection, and severe trauma models. In this study, we observe that splenic CD11b(+) cells markedly increase after experimental autoimmune encephalomyelitis (EAE) immunization, and they suppress T cell proliferation in vitro. Although >80% of CD11b(+) cells express varying levels of Gr-1, only a small population of CD11b(+)Ly-6C(high) inflammatory monocytes (IMC) can efficiently suppress T cell proliferation and induce T cell apoptosis through the production of NO. IFN-gamma produced by activated T cells is essential to induce IMC suppressive function. EAE immunization increases the frequencies of IMC in the bone marrow, spleen, and blood, but not in the lymph nodes. At the peak of EAE, IMC represent approximately 30% of inflammatory cells in the CNS. IMC express F4/80 and CD93 but not CD31, suggesting that they are immature monocytes. Furthermore, IMC have the plasticity to up-regulate NO synthase 2 or arginase 1 expression upon different cytokine treatments. These findings indicate that CD11b(+)Ly-6C(high) IMC induced during EAE priming are powerful suppressors of activated T cells. Further understanding of suppressive monocytes in autoimmune disease models may have important clinical implications for human autoimmune diseases.

Distinct regulation of MHC molecule expression on astrocytes and microglia during viral encephalomyelitis

The potential interplay of glial cells with T cells during viral induced inflammation was assessed by comparing major histocompatibility complex molecule upregulation and retention on astrocytes and microglia. Transgenic mice expressing green fluorescent protein under control of the astrocyte‐specific glial fibrillary acidic protein promoter were infected with a neurotropic coronavirus to facilitate phenotypic characterization of astrocytes and microglia using flow cytometry. Astrocytes in the adult central nervous system up‐regulated class I surface expression, albeit delayed compared with microglia. Class II was barely detectable on astrocytes, in contrast to potent up‐regulation on microglia. Maximal MHC expression in both glial cell types correlated with IFN‐γ levels and lymphocyte accumulation. Despite a decline of IFN‐γ concomitant to virus clearance, MHC molecule expression on glia was sustained. These data demonstrate distinct regulation of both class I and class II expression by microglia and astrocytes in vivo following viral induced inflammation. Furthermore, prolonged MHC expression subsequent to viral clearance implies a potential for ongoing presentation. © 2007 Wiley‐Liss, Inc.

Combination therapies for multiple sclerosis: scientific rationale, clinical trials, and clinical practice

PURPOSE OF REVIEW

To outline the scientific rationale for combination therapy in multiple sclerosis and to discuss the evidence for combination treatment strategies from animal models and clinical trials of multiple sclerosis.

RECENT FINDINGS

Experiments conducted in experimental autoimmune encephalomyelitis have recently shown beneficial effects of numerous combination therapies. The combination of approved and experimental drugs and two or more experimental agents may positively impact clinical disease activity, inflammation within the central nervous system, and neurorepair. Clinical trials are currently underway to establish the therapeutic efficacy and safety of various combination therapies for multiple sclerosis patients.

SUMMARY

More effective therapies are needed to treat multiple sclerosis. There are good scientific rationales for the use of combination therapy in multiple sclerosis, and the pharmacologic principles for evaluating and understanding their actions are available. The evaluation of specific combination therapies in the controlled setting of clinical trials should be a priority in clinical multiple sclerosis research.

Role of the MHC2TA gene in autoimmune diseases

OBJECTIVES

Expression of major histocompatibility complex (MHC) class II genes is almost exclusively regulated by the class II transactivator. A promoter polymorphism (-168A/G, rs3087456) in the MHC2TA gene was associated with increased susceptibility to rheumatoid arthritis, multiple sclerosis and myocardial infarction in a northern European population. However, no evidence of association of this MHC2TA variant with the two autoimmune diseases could be subsequently detected in independent cohorts.

AIM

To test the aforementioned single nucleotide polymorphism and another G-->C change (nt1614 from coding sequence, rs4774) to analyse the haplotype pattern in this MHC2TA gene.

METHODS

A case-control study was performed with 350 patients with rheumatoid arthritis, 396 patients with multiple sclerosis, 663 patients with inflammatory bowel disease (IBD) and 519 healthy controls from Madrid. Genotyping was ascertained by using TaqMan assays-on-demand on a 7900HT analyser, following the manufacturer's suggestions (Applied Biosystems, Foster City, California, USA). Haplotypes were inferred with the expectation-maximisation algorithm implemented by the Arlequin software.

RESULTS

No independent association with these autoimmune diseases was found for either polymorphism in the Spanish cohorts tested. However, when haplotypes were compared between patients with rheumatoid arthritis and controls, a significant difference in their overall frequency distribution was observed, evidencing a protective haplotype (-168A/1614C, p = 0.006; odds ratio (OR) 0.7) and a risk haplotype (-168G/1614C, p = 0.019; OR 1.6). Patients with multiple sclerosis mirrored these results, but no effect on IBD was identified.

CONCLUSIONS

The MHC2TA gene influences predisposition to rheumatoid arthritis and multiple sclerosis, but not to IBD. The -168G allele is not an aetiological variant in itself, but a genetic marker of susceptibility/protection haplotypes.

Heme oxygenase-1 and carbon monoxide suppress autoimmune neuroinflammation

Heme oxygenase-1 (HO-1, encoded by HMOX1) dampens inflammatory reactions via the catabolism of heme into CO, Fe, and biliverdin. We report that expression of HO-1 dictates the pathologic outcome of experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis (MS). Induction of EAE in Hmox1(-/- )C57BL/6 mice led to enhanced CNS demyelination, paralysis, and mortality, as compared with Hmox1(+/+) mice. Induction of HO-1 by cobalt protoporphyrin IX (CoPPIX) administration after EAE onset reversed paralysis in C57BL/6 and SJL/J mice and disease relapse in SJL/J mice. These effects were not observed using zinc protoporphyrin IX, which does not induce HO-1. CoPPIX protection was abrogated in Hmox1(-/-) C57BL/6 mice, indicating that CoPPIX acts via HO-1 to suppress EAE progression. The protective effect of HO-1 was associated with inhibition of MHC class II expression by APCs and inhibition of Th and CD8 T cell accumulation, proliferation, and effector function within the CNS. Exogenous CO mimicked these effects, suggesting that CO contributes to the protective action of HO-1. In conclusion, HO-1 or exposure to its end product CO counters autoimmune neuroinflammation and thus might be used therapeutically to treat MS.

Simvastatin inhibits interferon-gamma-induced MHC class II up-regulation in cultured astrocytes

Based on their potent anti-inflammatory properties and a preliminary clinical trial, statins (HMG-CoA reductase inhibitors) are being studied as possible candidates for multiple sclerosis (MS) therapy. The pathogenesis of MS is unclear. One theory suggests that the development of autoimmune lesions in the central nervous system may be due to a failure of endogenous inhibitory control of MHC class II expression on astrocytes, allowing these cells to adapt an interferon (IFN)-gamma-induced antigen presenting phenotype. By using immunocytochemistry in cultured astrocytes derived from newborn Wistar rats we found that simvastatin at nanomolar concentrations inhibited, in a dose-response fashion, up to 70% of IFN-gamma-induced MHC class II expression. This effect was reversed by the HMG-CoA reductase product mevalonate. Suppression of the antigen presenting function of astrocytes might contribute to the beneficial effects of statins in MS.

Efficient presentation of myelin oligodendrocyte glycoprotein peptides but not protein by astrocytes from HLA-DR2 and HLA-DR4 transgenic mice

The role of astrocytes in the pathogenesis of multiple sclerosis (MS) is not well understood. Astrocytes may modulate the activity of pathogenic T cells by presenting myelin antigens in combination with pro- or anti-inflammatory signals. Astrocytes have been shown to present myelin basic protein (MBP) and proteolipid protein (PLP) to T cells, but it has remained unresolved whether astrocytes present myelin oligodendrocyte glycoprotein (MOG), which has been implicated as an important autoantigen in MS. Here, we asked whether astrocytes presented MOG to T cells. To closer model presentation of human MOG by astrocytes in MS patients, we generated astrocytes from transgenic mice expressing the MS-associated MHC class II alleles HLA-DR2 (DRB1*1501) and HLA-DR4 (DRB1*0401). The results show that IFN-gamma-activated HLA-DR2 and HLA-DR4 expressing astrocytes efficiently presented immunodominant and subdominant MOG peptides to T cells. The hierarchy of the presented MOG epitopes was comparable to that of professional APCs, including dendritic cells and microglia. Importantly, astrocytes were poor at processing and presenting native MOG protein. Furthermore, astrocytes induced a mixed Th1/Th2 cytokine response in MOG-specific T cells, whereas dendritic cells induced a predominantly Th1 cell response. Collectively, the results suggest that astrocytes may modulate anti-MOG T cell responses in the CNS.

Vitamin K2 ameliorates experimental autoimmune encephalomyelitis in Lewis rats

Vitamin K2 (VK2), which has been in wide use for the management of hypoprothrombinemia and osteoporosis in Japan, was tested for its efficacy on experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). The severity of EAE was significantly ameliorated by the prophylactic administration of VK2, though it was not effective when given after the onset. Inflammatory cellular infiltration and the expression of both MHC class II and inducible nitric oxide synthase (iNOS) were reduced in the spinal cords of VK2-treated rats with EAE. The inhibitory effect of VK2 on the iNOS expression in glial cells was also observed in vitro. Considering the long use of VK2 without noticeable untoward effects, it may be applicable to the patients with MS.

Astrocytes as antigen-presenting cells: expression of IL-12/IL-23

Interleukin-12 (IL-12, p70) a heterodimeric cytokine of p40 and p35 subunits, important for Th1-type immune responses, has been attributed a prominent role in multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE). Recently, the related heterodimeric cytokine, IL-23, composed of the same p40 subunit as IL-12 and a unique p19 subunit, was shown to be involved in Th1 responses and EAE. We investigated whether astrocytes and microglia, CNS cells with antigen-presenting cell (APC) function can present antigen to myelin basic protein (MBP)-reactive T cells, and whether this presentation is blocked with antibodies against IL-12/IL-23p40. Interferon (IFN)-gamma-treated APC induced proliferation of MBP-reactive T cells. Anti-IL-12/IL-23p40 antibodies blocked this proliferation. These results support and extend our previous observation that astrocytes and microglia produce IL-12/IL-23p40. Moreover, we show that stimulated astrocytes and microglia produce biologically active IL-12p70. Because IL-12 and IL-23 share p40, we wanted to determine whether astrocytes also express IL-12p35 and IL-23p19, as microglia were already shown to express them. Astrocytes expressed IL-12p35 mRNA constitutively, and IL-23 p19 after stimulation. Thus, astrocytes, under inflammatory conditions, express all subunits of IL-12/IL-23. Their ability to present antigen to encephalitogenic T cells can be blocked by neutralizing anti-IL-12/IL-23p40 antibodies.

MHC2TA is associated with differential MHC molecule expression and susceptibility to rheumatoid arthritis, multiple sclerosis and myocardial infarction

Antigen presentation to T cells by MHC molecules is essential for adaptive immune responses. To determine the exact position of a gene affecting expression of MHC molecules, we finely mapped a previously defined rat quantitative trait locus regulating MHC class II on microglia in an advanced intercross line. We identified a small interval including the gene MHC class II transactivator (Mhc2ta) and, using a map over six inbred strains combined with gene sequencing and expression analysis, two conserved Mhc2ta haplotypes segregating with MHC class II levels. In humans, a -168A --> G polymorphism in the type III promoter of the MHC class II transactivator (MHC2TA) was associated with increased susceptibility to rheumatoid arthritis, multiple sclerosis and myocardial infarction, as well as lower expression of MHC2TA after stimulation of leukocytes with interferon-gamma. We conclude that polymorphisms in Mhc2ta and MHC2TA result in differential MHC molecule expression and are associated with susceptibility to common complex diseases with inflammatory components.

Dendritic cells permit immune invasion of the CNS in an animal model of multiple sclerosis

Immunization with myelin antigens leads to the development of experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. The disease can also be induced by the transfer of encephalitogenic CD4+ T helper (T(H)) lymphocytes into naive mice. These T cells need to re-encounter their cognate antigen in the context of major histocompatibility complex (MHC) class II-bearing antigen-presenting cells (APCs) in order to recognize their target. The cell type and location of the APC mediating T-cell entry into the central nervous system (CNS) remain unknown. Here, we show that APCs of the lymphoreticular system and of the CNS parenchyma are dispensable for the immune invasion of the CNS. We also describe that a discrete population of vessel-associated dendritic cells (DCs) is present in human brain tissue. In mice, CD11c+ DCs alone are sufficient to present antigen in vivo to primed myelin-reactive T cells in order to mediate CNS inflammation and clinical disease development.

Beneficial effect of erythropoietin on experimental allergic encephalomyelitis

We have known for a long time that erythropoietin signaling plays a key role in bone marrow erythrocyte proliferation. However, recent studies have indicated that erythropoietin also may have protective effects on the nervous system. This unexpected role remains incompletely characterized. To investigate the potential neuroprotective role of erythropoietin in the central nervous system, we assessed its effects on a well-characterized autoimmune demyelinating model of multiple sclerosis-myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis (EAE) in the mouse. We found that erythropoietin administered intravenously for 14 days after the onset of symptoms reduced both disease severity and duration of maximum impairment at dose levels as low as 50U/kg (p < 0.001). We assessed the neuropathology of diseased spinal cords and found that erythropoietin-treated EAE animals had reduced axonal damage, inflammatory cell infiltration and demyelination, and diminished blood-brain barrier leakage when compared with saline-treated EAE controls. Moreover, the pronounced upregulation of spinal cord major histocompatibility complex (MHC) class II expression found in saline-treated EAE was significantly reduced in erythropoietin-treated animals, a finding we replicated in vitro, using microglial cultures. The notion that short-term erythropoietin therapy might be of clinical benefit in human autoimmune demyelinating diseases needs investigation.

? lipoic acid inhibits human T-cell migration: Implications for multiple sclerosis

We have demonstrated previously the ability of the antioxidant alpha lipoic acid (ALA) to suppress and treat a model of multiple sclerosis (MS), relapsing experimental autoimmune encephalomyelitis (EAE). We describe the effects of ALA and its reduced form, dihydrolipoic acid (DHLA), on the transmigration of human Jurkat T cells across a fibronectin barrier in a transwell system. ALA and DHLA inhibited migration of Jurkat cells in a dose-dependent fashion by 16-75%. ALA and DHLA reduced matrix metalloproteinase-9 (MMP-9) activity by 18-90% in Jurkat cell supernatants. GM6001, a synthetic inhibitor of MMP, reduced Jurkat cell migration, but not as effectively as ALA and DHLA did. Both ALA and DHLA downmodulated the surface expression of the alpha4beta1 integrin (very late activation-4 antigen; VLA-4), which binds fibronectin and its endothelial cell ligand vascular cell adhesion molecule-1 (VCAM-1). Moreover, ALA, but not DHLA, reduced MMP-9-specific mRNA and extracellular MMP-9 from Jurkat cells and their culture supernatants as detected by relative reverse transcriptase-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA), respectively. ALA and DHLA inhibited Jurkat cell migration and have different mechanisms for inhibiting MMP-9 activity. These data, coupled with its ability to treat relapsing EAE, suggest that ALA warrants investigation as a therapy for MS.

Regulation of MHC class II expression in glioma cells by class II transactivator (CIITA)

We first classified 12 malignant glioma cell lines into three different groups (types 1-3) with respect to major histocompatibility complex (MHC) class II expression and analyzed each group based on the different expression status of the class II transactivator (CIITA) gene. Glioma type 1 (2 of 12) showed constitutive expression of all class II molecules that might be mediated by activation of B cell-specific CIITA promoter III. Glioma type 2 represented the major phenotype (66.7 %) of malignant glioma cell lines, and MHC class II expression was induced by interferon-gamma (IFN-gamma) in this phenotype. Analysis of glioma tissue samples revealed that CIITA promoter IV was detected in 9 of 11 patients (81.8%); however, promoter III was only in two (18.2%). Moreover, cultured glioma cells obtained from a fresh tumor sample upregulated expression of CIITA and class II molecules in the presence of IFN-gamma, strongly suggesting that glioma type 2 might be predominant in glioma tissues. Glioma type 3 (2 of 12) showed CIITA transcripts but loss of MHC class II expression even in the presence of IFN-gamma. In addition, we determined that the constitutive MHC class II expression in the glioma cell lines (type 1) was the result of transcriptional activation of the CIITA gene. This phenomenon was mediated by global histone acetylation over 6 kb upstream from the transcriptional start site of CIITA promoter III. Moreover, stable transfection of CIITA promoter IV as well as promoter III into MHC class II inducible cell lines restored the constitutive expression of all class II molecules. These studies lay the foundation to understand the molecular basis for the expression of class II molecules in gliomas.

In vitro biological activity of anti-C II TA hammerhead ribozyme--a novel approach for autoimmune diseases

This study investigated the feasibility of using an hammerhead ribozyme against C II TA, a major regulator of MHC II antigens, to repress the expression of MHC II molecules on Hela cells. A hammerhead ribozyme (Rz464) specific to 463-465 GUC triplet of C II TA and its target gene were transcribed, then mixed up and incubated in vitro. The cleavage products were analyzed by PAGE and silver-staining. Rz464 was then inserted into the pIRES2-EGFP vector (pRz464). Stable transfectants of Hela with pRz464 were tested for class II MHC induction by recombinant human interferon-gamma (IFN-gamma). mRNA of C II TA was measured by RT-PCR. Our results showed that Rz464 could exclusively cleave C II TA RNA. When induced with IFN-gamma, the expression of HLA-DR, -DP, -DQ on pRz464+ Hela was induced, and the mRNA content of C II TA decreased too. It is concluded that Rz464 could inhibit C II TA and thus the family of genes was regulated by C II TA:MHC II molecules. These results provided insight into the future application of Rz464 as a new nucleic acid drug against auto-immune diseases.

Diverse targets for intervention during inflammatory and neurodegenerative phases of multiple sclerosis

Multiple sclerosis (MS) is an autoimmune central nervous system (CNS) demyelinating disease that causes relapsing and chronic neurologic impairment. Recent observations have altered certain traditional concepts regarding MS pathogenesis. A greater diversity of cell types and molecules involved in MS is now evident. While remyelination can occur during the early inflammatory phase when damage may be reversible, it is impaired in the later stages, which involve axonal death. These observations have important therapeutic implications.

Repression of allo-cell transplant rejection through CIITA ribonuclease P+ hepatocyte

AIM: Allo-cell transplant rejection and autoimmune responses were associated with the presence of class II major histocompatibility complex (MHC II) molecules on cells. This paper studied the effect of Ribonuclease P (RNase P) against CIITA, which was a major regulator of MHCII molecules, on repressing the expression of MHCII molecules on hepatocyte.

METHODS: M1-RNA is the catalytic RNA subunit of RNase P from Escherichia coli. It were constructed that M1-RNA with guide sequences (GS) recognizing the 452, 3408 site of CIITA by PCR from pTK117 plasmid, then were cloned into the EcoR I/Bgl II or EcoR I/Sal I site of vector psNAV (psNAV-M1-452-GS, psNAV-M1-3408-GS) respectively. The target mould plate (3176-3560) of CIITA was obtained from Raji cell by RT-PCR, and then inserted into the Xho I/EcoR I of pGEM-7zf(+) plasmid (pGEM-3176). These recombinant plasmids were screened out by sequence analysis. psNAV-M1-452-GS, psNAV-M1-3408-GS and its target RNA pGEM-3176 were transcribed and then mixed up and incubated in vitro. It showed that M1-3408-GS could exclusively cleave target RNA that formed a base pair with the GS. Stable transfectants of hepatocyte cell line with psNAV-M1-3408-GS were tested for expression of class II MHC through FCM, for mRNA abundance of MHCII, Ii and CIITA by RT-PCR, for the level of IL-2 mRNA on T cell by mixed lymphocyte reaction.

RESULTS: When induced with recombinant human interferon-gamma (IFN-γ), the expression of HLA-DR, -DP, -DQ on psNAV-M1-3408-GS⁺ hepatocyte was reduced 83.27%, 88.93%, 58.82% respectively, the mRNA contents of CIITA, HLA-DR, -DP, -DQ and Ii decreased significantly. While T cell expressed less IL-2 mRNA in the case of psNAV-M1-3408-GS⁺ hepatocyte.

CONCLUSION: The Ribonuclease P against CIITA-M1-3408-GS could effectively induce antigen-specific tolerance through cleaving CIITA. These results provided insight into the future application of M1-3408-GS as a new nucleic acid drug against allo-transplantation rejection and autoimmune diseases.