Jeffrey J. Bajramovic

Differential expression of stress proteins in human adult astrocytes in response to cytokines

Various lines of evidence suggest a close relationship between heat shock proteins (hsp) and several autoimmune diseases such as arthritis, diabetes and multiple sclerosis. While enhanced expression of hsp in autoimmune diseases is often regarded as a non-specific bystander effect of the inflammatory process, surprisingly little is known on hsp regulation by inflammatory mediators such as cytokines. In this study cytokine-induced expression of hsp60, hsp27 and alphaB-crystallin was studied in cultures of primary human adult astrocytes at the mRNA as well as at the protein level. We show differential hsp expression patterns in response to pro-inflammatory and immunoregulatory cytokines. Hsp60 expression was found to be enhanced in response to cytokines as diverse as IL-1beta, TNF-alpha, IL-4, IL-6 and IL-10. Upregulation of hsp27, however, was primarily induced by immunoregulatory cytokines like IL-4, IL-6 and TGF-beta whereas alphaB-crystallin expression was found to be enhanced by the pro-inflammatory cytokine TNF-alpha only. None of the cytokines studied was able to enhance expression of all three hsp simultaneously. These results show that in human astrocytes induced expression of hsp27 and alphaB-crystallin is dependent on the presence of a defined set of stimuli, while induced expression of hsp60 is a much less selective event. This highly differential pattern of hsp expression in response to inflammatory mediators known to play an important role in the pathogenesis of autoimmune diseases indicates that hsp responses are specific rather than non-specific bystander responses.

αB-Crystallin Is a Target for Adaptive Immune Responses and a Trigger of Innate Responses in Preactive Multiple Sclerosis Lesions

We present the first comparative analysis of serum immunoglobulinG reactivity profiles against the full spectrum of human myelin-associated proteins in multiple sclerosis patients and healthy control subjects. In both groups, serum antibodies display a consistent and prominent reaction to &agr;B-crystallin (CRYAB) versus other myelin proteins. As an apparently major target for the adaptive immune system in humans, CRYAB selectively accumulates in oligodendrocytes, but not in astrocytes, or axons in so-called preactive multiple sclerosis lesions. These are clusters of activated HLA-DR-expressing microglia in myelinated normal-appearing white matter with no obvious leukocyte infiltration. They are found in most multiple sclerosis patients at all stages of disease. In these lesion areas, CRYAB in oligodendrocytes may come directly in contact with activated HLA-DR+ microglia. We demonstrate that CRYAB activates innate responses bymicroglia by stimulating the secretion of leukocyte-recruiting factors, including tumor necrosis factor, interleukin 17, CCL5, and CCL1, and immune-regulatory cytokines such as interleukin 10, transforming growth factor-&bgr;, and interleukin 13. Together, these data suggest that CRYAB accumulation in preactive lesions may be part of a reversible reparative local response that involves both oligodendrocytes and microglia. At the same time, however, accumulated CRYAB may represent a major target for adaptive immune responses that could contribute to progression of preactive lesions to a stage of demyelination.

Presentation of αB-Crystallin to T Cells in Active Multiple Sclerosis Lesions: An Early Event Following Inflammatory Demyelination

In the development of multiple sclerosis (MS), (re)activation of infiltrating T cells by myelin-derived Ags is considered to be a crucial step. Previously, αB-crystallin has been shown to be an important myelin Ag to human T cells. Since αB-crystallin is an intracellular heat shock protein, the question arises at what stage, if any, during lesional development in MS this Ag becomes available for CD4+ T cells. In 3 of 10 active MS lesions, αB-crystallin could be detected inside phagocytic vesicles of perivascular macrophages, colocalizing with myelin basic protein and myelin oligodendrocyte glycoprotein (MOG). Although the detectability of MOG in phagosomes is considered as a marker for very recent demyelination, MOG was detected in more macrophages and in more lesions than αB-crystallin. The disappearance of αB-crystallin from macrophages even before MOG was confirmed by in vitro studies; within 6 h after myelin-uptake αB-crystallin disappears from the phagosomes. αB-Crystallin-containing macrophages colocalized with infiltrating T cells and they were characterized by expression of MHC class II, CD40, and CD80. To examine functional presentation of myelin Ags to T cells, purified macrophages were pulsed in vitro with whole myelin membranes. These macrophages activated both myelin-primed and αB-crystallin-primed T cells in terms of proliferation and IFN-γ secretion. In addition, αB-crystallin-pulsed macrophages activated myelin-primed T cells to the same extent as myelin-pulsed macrophages, whereas myelin basic protein-pulsed macrophages triggered no response at all. These data indicate that, in active MS lesions, αB-crystallin is available for functional presentation to T cells early during inflammatory demyelination.

Preclinical development of monoclonal antibodies: considerations for the use of non-human primates.

The development of mAbs remains high on the therapeutic agenda for the majority of pharmaceutical and biotechnology companies. Often, the only relevant species for preclinical safety assessment of mAbs are non-human primates (NHPs), and this raises important scientific, ethical and economic issues. To investigate evidence-based opportunities to minimize the use of NHPs, an expert working group with representatives from leading pharmaceutical and biotechnology companies, contract research organizations and institutes from Europe and the USA, has shared and analyzed data on mAbs for a range of therapeutic areas. This information has been applied to hypothetical examples to recommend scientifically appropriate development pathways and study designs for a variety of potential mAbs. The addendum of ICHS6 provides a timely opportunity for the scientific and regulatory community to embrace strategies which minimize primate use and increase efficiency of mAb development.

The Microtubule Regulator Stathmin Is an Endogenous Protein Agonist for TLR3

TLR3 recognizes dsRNAs and is considered of key importance to antiviral host-defense responses. TLR3 also triggers neuroprotective responses in astrocytes and controls the growth of axons and neuronal progenitor cells, suggesting additional roles for TLR3-mediated signaling in the CNS. This prompted us to search for alternative, CNS-borne protein agonists for TLR3. A genome-scale functional screening of a transcript library from brain tumors revealed that the microtubule regulator stathmin is an activator of TLR3-dependent signaling in astrocytes, inducing the same set of neuroprotective factors as the known TLR3 agonist polyinosinic:polycytidylic acid. This activity of stathmin crucially depends on a long, negatively charged α helix in the protein. Colocalization of stathmin with TLR3 on astrocytes, microglia, and neurons in multiple sclerosis-affected human brain indicates that as an endogenous TLR3 agonist, stathmin may fulfill previously unsuspected regulatory roles during inflammation and repair in the adult CNS.

CNS myelin induces regulatory functions of DC-SIGN-expressing, antigen-presenting cells via cognate interaction with MOG

Human myelin oligodendrocyte glycoprotein is decorated with fucosylated N-glycans that are recognized by DC-SIGN+ DCs and microglia that control immune homeostasis.

The design of chronic toxicology studies of monoclonal antibodies: implications for the reduction in use of non-human primates.

The changing environment of monoclonal antibody (mAb) development is impacting on the cost of drug development and the use of experimental animals, particularly non-human primates (NHPs). The drive to reduce these costs is huge and involves rethinking and improving nonclinical studies to make them more efficient and more predictive of man. While NHP use might be unavoidable in many cases because of the exquisite specificity and consequent species selectivity of mAbs, our increasing knowledge base can be used to improve drug development and maximise the output of experimental data. Data on GLP regulatory toxicology studies for 58mAbs were obtained from 10 companies across a wide range of therapeutic indications. These data have been used to investigate current practice and identify study designs that minimise NHP use. Our analysis shows that there is variation in the number of animals used for similar studies. This information has been used to develop practical guidance and make recommendations on the use of science-based rationale to design studies using fewer animals taking into account the current regulatory guidance. There are eight recommendations intended to highlight areas for consideration. They include guidance on the main group size, the inclusion of recovery groups and the number of dose groups used in short and long term chronic toxicology studies.

The human CMV-UL86 peptide 981-1003 shares a crossreactive T-cell epitope with the encephalitogenic MOG peptide 34-56, but lacks the capacity to induce EAE in rhesus monkeys

Rhesus monkeys immunized with MOG(34-56), a dominant T-cell epitope from myelin/oligodendrocyte glycoprotein, develop an acute neurological disease resembling acute disseminated encephalomyelitis (ADEM) in humans. The typical large demyelinated lesions and mononuclear infiltrates in the monkey brains are caused by MOG(34-56) T-cells. We show that MOG(34-56)-reactive CD4+ and CD8+ T-cells are induced in monkeys immunized with a peptide from the human CMV major capsid protein (UL86; 981-1003), that shares sequence similarity with MOG(34-56). Monkeys sensitized against the viral peptide and subsequently challenged with MOG(34-56) display histological signs of encephalitis, but do not show overt neurological signs.

Identification of Soluble CD14 as an Endogenous Agonist for Toll-Like Receptor 2 on Human Astrocytes by Genome-Scale Functional Screening of Glial Cell Derived Proteins

Human astrocytes express a limited repertoire of Toll‐like receptor (TLR) family members including TLR1‐4, which are expressed on the cell surface. Also, TLR3 but not TLR4 activation on astrocytes induces expression of several factors involved in neuroprotection and down‐regulation of inflammation rather than in the onset of traditional pro‐inflammatory reactions. The notion that astrocyte TLR may thus play a role not only in host defense but also in tissue repair responses prompted us to examine the possibility that endogenous TLR agonists could be expressed in the human central nervous system to regulate the apparently dual astrocyte functions during trauma or inflammation. As a potential source of endogenous agonists, a cDNA library derived from several human brain tumor cell lines was used. Gene pools of this library were transfected into COS‐7 cells and the expression products were screened for their ability to induce TLR activation in human primary astrocytes. The screening resulted in the identification of soluble CD14. By using a panel of TLR‐transfected HEK293 cells, we found that signaling by soluble CD14 was TLR2 dependent. Moreover, the CD14‐triggered TLR2‐mediated response in astrocytes lead to the production of CXCL8, IL‐6, and IL12p40, whereas typical TLR‐induced pro‐inflammatory cytokines, like TNF‐α and IL‐1β, were not produced at detectable levels. In conclusion, our data indicate that apart from its well‐known ability to act as a co‐receptor for TLR‐dependent signaling by peptidoglycans or LPS, soluble CD14 can also act as a direct agonist for TLR2.

Chapter 30 The small heat shock protein αB-crystallin as key autoantigen in multiple sclerosis

Publisher Summary Multiple sclerosis (MS) is the most common neurological disease of young adults in the Western world, affecting about 1 per 1,000. The hallmark of MS is the chronic development of inflammatory demyelinating lesions in central nervous system (CNS) white matter. Several mechanisms have been put forward to explain the possible relationship between anti-viral immunity and CNS myelin-reactive immune responses presumed to precipitate MS. These mechanisms include molecular mimicry (structural similarity between pathogen-specific determinants and CNS myelin determinants) causing pathogen-activated T cells to cross-react against CNS myelin, superantigenic stimulation of myelin-reactive T cells or bystander reactivity to myelin antigens released as the result of cytopathic viral infection of glia cells. Recently, we have collected evidence for yet another mechanism: virus-induced peripheral presentation to helper T cells of the small HSP αB-crystallin, the very same protein that is a known immunodominant T-cell antigen of CNS myelin. This is discussed in this chapter.