Alpha B-crystallin is not a dominant peripheral T-cell autoantigen in multiple sclerosis amongst Sardinians

The CD8 T Cell-Epstein-Barr Virus-B Cell Trialogue: A Central Issue in Multiple Sclerosis Pathogenesis

The cause and the pathogenic mechanisms leading to multiple sclerosis (MS), a chronic inflammatory disease of the central nervous system (CNS), are still under scrutiny. During the last decade, awareness has increased that multiple genetic and environmental factors act in concert to modulate MS risk. Likewise, the landscape of cells of the adaptive immune system that are believed to play a role in MS immunopathogenesis has expanded by including not only CD4 T helper cells but also cytotoxic CD8 T cells and B cells. Once the key cellular players are identified, the main challenge is to define precisely how they act and interact to induce neuroinflammation and the neurodegenerative cascade in MS. CD8 T cells have been implicated in MS pathogenesis since the 80's when it was shown that CD8 T cells predominate in MS brain lesions. Interest in the role of CD8 T cells in MS was revived in 2000 and the years thereafter by studies showing that CNS-recruited CD8 T cells are clonally expanded and have a memory effector phenotype indicating in situ antigen-driven reactivation. The association of certain MHC class I alleles with MS genetic risk implicates CD8 T cells in disease pathogenesis. Moreover, experimental studies have highlighted the detrimental effects of CD8 T cell activation on neural cells. While the antigens responsible for T cell recruitment and activation in the CNS remain elusive, the high efficacy of B-cell depleting drugs in MS and a growing number of studies implicate B cells and Epstein-Barr virus (EBV), a B-lymphotropic herpesvirus that is strongly associated with MS, in the activation of pathogenic T cells. This article reviews the results of human studies that have contributed to elucidate the role of CD8 T cells in MS immunopathogenesis, and discusses them in light of current understanding of autoreactivity, B-cell and EBV involvement in MS, and mechanism of action of different MS treatments. Based on the available evidences, an immunopathological model of MS is proposed that entails a persistent EBV infection of CNS-infiltrating B cells as the target of a dysregulated cytotoxic CD8 T cell response causing CNS tissue damage.

The link between small heat shock proteins and the immune system

There is now compelling evidence that members of the family of small heat shock proteins (HSP) can be secreted by a variety of different types of cells. Secretion of small HSP may at times represent altruistic delivery of supporting and stabilizing factors from one cell to another. A probably more general effect of extracellular small HSP, however, is exerted by their ability to activate macrophages and macrophage-like cells. When doing so, small HSP induce an immune-regulatory state of activation, stimulating macrophages to suppress inflammation. For this reason, small HSP deserve consideration as broadly applicable therapeutic agents for inflammatory disorders. In one particular case, however, adaptive immune responses to the small HSP itself may subvert the protective quality of the innate immune response it triggers. This situation only applies to alpha B-crystallin, and is unique for humans as well. In this special case, local concentrations of alpha B-crystallin determine the balance between protective innate responses and destructive adaptive responses, the latter of which are held responsible for the development of multiple sclerosis lesions. This article is part of a Directed Issue entitled: Small HSPs in physiology and pathology.

Chaperone activity of α B-crystallin is responsible for its incorrect assignment as an autoantigen in multiple sclerosis

For 15 y, α B-crystallin (heat shock protein [Hsp] B5) has been labeled an autoantigen in multiple sclerosis (MS) based on humoral and cellular responses found in humans and animal models. However, there have been several scientific inconsistencies with this assignment, ranging from studies demonstrating small differences in anticrystallin responses between patients and healthy individuals to the inability of crystallin-specific T cells to induce symptoms of experimental allergic encephalomyelitis in animal models. Experiments in this article demonstrate that the putative anti-HspB5 Abs from 23 MS patients cross-react with 7 other members of the human small Hsp family and were equally present in normal plasma. Biolayer interferometry demonstrates that the binding was temperature dependent, and that the calculated K(a) increased as the concentration of the sHsp decreased. These two patterns are characteristic of multiple binding sites with varying affinities, the composition of which changes with temperature, supporting the hypothesis that HspB5 bound the Ab and not the reverse. HspB5 also precipitated Ig heavy and L chains from sera from patients with MS. These results establish that small Hsps bind Igs with high affinity and refute much of the serological data used to assign α B-crystallin as an autoantigen.

AlphaB-crystallin-reactive T cells from knockout mice are not encephalitogenic

Alpha B-crystallin (alphaB) is a small heat shock protein that is strongly up-regulated in multiple sclerosis (MS) brain tissue, and can induce strong T cell responses. Assessing a potential encephalitogenic function for alphaB protein in MS and experimental autoimmune encephalomyelitis (EAE) has been challenging due to its ubiquitous expression that likely maintains central and peripheral tolerance to this protein in mice. To address this issue, we obtained alphaB-knockout (alphaB-KO) mice in H-2b background that lack immune tolerance to alphaB protein, and thus are capable of developing alphaB-specific T cells that could be tested for encephalitogenic activity after transfer into alphaB-expressing wild type (WT) mice. We found that T cell lines from spleens of alphaB protein-immunized alphaB-KO mice proliferated strongly to alphaB protein itself, and the majority of T cells were CD4+ and capable of secreting pro-inflammatory Th1 cytokines upon restimulation. However, transfer of such alphaB-reactive T cells back into WT recipients was not sufficient to induce EAE, compared to the transfer of mouse MOG-35-55 peptide-reactive T cells from the same donors that induced severe EAE in recipients. Moreover, alphaB-specific T cells failed to augment severity of actively induced EAE in WT mice that were expressing high levels of alphaB message in the CNS at the time of transfer. These results suggest that alphaB-specific T cells are immunocompetent but not encephalitogenic in 129SvEv mice, and that immune tolerance may not be the main factor that limits the encephalitogenic potential of alphaB.

Genes, environment, and susceptibility to multiple sclerosis

Multiple sclerosis (MS) is a chronic disease of the central nervous system affecting young adults and thus representing a major burden also for their families and communities. The etiology of MS is obscure and its pathogenesis is yet incompletely depicted. Increased evidences indicate a strong genetic contribution to MS susceptibility, although others support the view that it is also influenced by environmental factors, possibly related to still unidentified pathogens. MS appears to be more heterogeneous than previously believed at the immunological level, and new pathological studies indicate a series of subset of conditions under the common denominator MS. The use of genetically homogeneous and geographically isolated populations at high MS risk, such as that of Sardinia, insular Italy, becomes in principle a vital requirement to reduce biological variables and the intrinsic complexity of the disease. This review will focus on recent findings on the peculiarity of Sardinian MS concerning epidemiological, genetic, and environmental aspects. Epidemiological studies reveal a clear heterogeneous distribution of MS cases in the Northern province of Sassari which may not be uniquely assigned to genetic variations. Furthermore, a different immunogenetic profile, including the association with other immunomediated diseases, and a progressive change in clinical phenotype, including age at onset, are present in this island which gives us unexpected variations at the level of patients' cohort and territorial distribution, especially when the northern province is compared to the southern one. This renders MS etiopathogenesis more complex than formerly thought even in this selected and genetically stable population.

CD4 T-cell epitopes of human alpha B-crystallin

Of potential importance to multiple sclerosis (MS), oligodendroglial alpha B-crystallin is expressed and associated with the myelin sheath at the earliest stage of MS lesion development. We selected T-cell lines specific for human alpha B-crystallin from peripheral blood mononuclear cells (PBMC) of HLA-DR2 homozygous MS patients and found that the alpha B-crystallin-specific T-cells were CD4+ and restricted by DRB1*1501, and expressed Th1 cytokines. The CD4 T-cell epitopes of human alpha B-crystallin were determined by proliferation of alpha B-crystallin-specific T-cell lines to 17 20-mer synthetic overlapping peptides spanning the entire molecule of human alpha B-crystallin. It was found that the HLA-DR2 donor-derived alpha B-crystallin-specific T-cell lines proliferated to alpha B-crystallin peptides 21-40, 41-60, and to a lesser extent, 131-150. These T-cell proliferation responses were associated with intracellular expression of interleukin-2 (IL-2) and secretion of interferon-gamma (IFN-gamma), and tumor necrosis factor-alpha (TNF-alpha). The amino acid sequences of these peptides were compatible with predicted HLA-DR2-restricted binding motifs. PBMC of an early active MS patient proliferated to the epitope-containing peptides significantly better than did those of later stage MS patients or healthy controls. Taken together, these findings suggest that autoreactive alpha B-crystallin-specific Th1 cells may have the potential to contribute to MS pathogenesis.