Heather A. Arnett

TNF alpha promotes proliferation of oligodendrocyte progenitors and remyelination.

Here we used mice lacking tumor necrosis factor-α (TNFα) and its associated receptors to study a model of demyelination and remyelination in which these events could be carefully controlled using a toxin, cuprizone. Unexpectedly, the lack of TNFα led to a significant delay in remyelination as assessed by histology, immunohistochemistry for myelin proteins and electron microscopy coupled with morphometric analysis. Failure of repair correlated with a reduction in the pool of proliferating oligodendrocyte progenitors (bromodeoxyuridine-labeled NG2+ cells) followed by a reduction in the number of mature oligodendrocytes. Analysis of mice lacking TNF receptor 1 (TNFR1) or TNFR2 indicated that TNFR2, not TNFR1, is critical to oligodendrocyte regeneration. This unexpected reparative role for TNFα in the CNS is important for understanding oligodendrocyte regeneration/proliferation, nerve remyelination and the design of new therapeutics for demyelinating diseases.

BTNL2, a Butyrophilin/B7-Like Molecule, Is a Negative Costimulatory Molecule Modulated in Intestinal Inflammation

Butyrophilin-like 2 (BTNL2) is a butyrophilin family member with homology to the B7 costimulatory molecules, polymorphisms of which have been recently associated through genetic analyses to sporadic inclusion body myositis and sarcoidosis. We have characterized the full structure, expression, and function of BTNL2. Structural analysis of BTNL2 shows a molecule with an extracellular region containing two sets of two Ig domains, a transmembrane region, and a previously unreported cytoplasmic tail. Unlike most other butyrophilin members, BTNL2 lacks the prototypical B30.2 ring domain. TaqMan and Northern blot analysis indicate BTNL2 is predominantly expressed in digestive tract tissues, in particular small intestine and Peyer’s patches. Immunohistochemistry with BTNL2-specific Abs further localizes BTNL2 to epithelial and dendritic cells within these tissues. Despite its homology to the B7 family, BTNL2 does not bind any of the known B7 family receptors such as CD28, CTLA-4, PD-1, ICOS, or B and T lymphocyte attenuator. Because of its localization in the gut and potential role in the immune system, BTNL2 expression was analyzed in a mouse model of inflammatory bowel disease. BTNL2 is overexpressed during both the asymptomatic and symptomatic phase of the Mdr1a knockout model of spontaneous colitis. In functional assays, soluble BTNL2-Fc protein inhibits the proliferation of murine CD4+ T cells from the spleen, mesenteric lymph node, and Peyer’s patch. In addition, BTNL2-Fc reduces proliferation and cytokine production from T cells activated by anti-CD3 and B7-related protein 1. These data suggest a role for BTNL2 as a negative costimulatory molecule with implications for inflammatory disease.

Mechanisms of Oncostatin M-Induced Pulmonary Inflammation and Fibrosis

Oncostatin M (OSM), an IL-6 family cytokine, has been implicated in a number of biological processes including the induction of inflammation and the modulation of extracellular matrix. In this study, we demonstrate that OSM is up-regulated in the bronchoalveolar lavage fluid of patients with idiopathic pulmonary fibrosis and scleroderma, and investigate the pathological consequences of excess OSM in the lungs. Delivery of OSM to the lungs of mice results in a significant recruitment of inflammatory cells, as well as a dose-dependent increase in collagen deposition in the lungs, with pathological correlates to characteristic human interstitial lung disease. To better understand the relationship between OSM-induced inflammation and OSM-induced fibrosis, we used genetically modified mice and show that the fibrotic response is largely independent of B and T lymphocytes, eosinophils, and mast cells. We further explored the mechanisms of OSM-induced inflammation and fibrosis using both protein and genomic array approaches, generating a “fibrotic footprint” for OSM that shows modulation of various matrix metalloproteinases, extracellular matrix components, and cytokines previously implicated in fibrosis. In particular, although the IL-4/IL-13 and TGF-β pathways have been shown to be important and intertwined of fibrosis, we show that OSM is capable of inducing lung fibrosis independently of these pathways. The demonstration that OSM is a potent mediator of lung inflammation and extracellular matrix accumulation, combined with the up-regulation observed in patients with pulmonary fibrosis, may provide a rationale for therapeutically targeting OSM in human disease.

The Protective Role of Nitric Oxide in a Neurotoxicant- Induced Demyelinating Model

Demyelination is often associated with acute inflammatory events involving the recruitment-activation of microglia/macrophage, astrocytes, and leukocytes. The ultimate role of inflammatory products in demyelinating disease and in the survival of oligodendrocytes, the myelin forming cells, is unresolved. The current study examines the role of inducible NO synthase (iNOS)-derived NO in a neurotoxicant-induced model of demyelination. NO levels were greatly elevated in the midline corpus callosum during demyelination in genetically intact C57BL/6 mice, and this NO was due solely to the induction of iNOS, as the correlates of NO were not found in mice lacking iNOS. C57BL/6 mice lacking iNOS exhibited more demyelination, but did not display an increased overall cellularity in the corpus callosum, attributable to an unimpeded microglia/macrophage presence. An enhanced course of pathology was noted in mice lacking iNOS. This was associated with a greater depletion of mature oligodendrocytes, most likely due to apoptosis of oligodendrocytes. Microglia and astrocytes did not undergo apoptosis during treatment. Our results suggest a moderately protective role for NO during acute inflammation-association demyelination.

Astroglial-derived lymphotoxin-α exacerbates inflammation and demyelination, but not remyelination

Tumor necrosis factorα (TNFα) and lymphotoxin‐α (Ltα) are upregulated in and around multiple sclerosis plaques and are proposed to play a role during chronic inflammation in demyelinating disease. Despite the perceived detrimental role of these cytokines, human clinical trials inhibiting TNFα signaling has led to worsening of symptoms in multiple sclerosis (MS) patients. Our laboratory has verified a role for TNFα in the exacerbation of demyelination but, more importantly, has demonstrated a novel role for TNFα in reparative remyelination in a cuprizone‐induced demyelination model. This may explain the worsening of symptoms experienced by MS patients. In view of the cross‐talk in TNF family signaling, the aim of this study is to understand the role of Ltα in demyelination and remyelination in hopes of improving therapeutic strategies for MS. Using the same model, we show that mice lacking Ltα exhibit a delay in demyelination that is greater than that exhibited by TNFα null mice. In this model, Ltα is expressed primarily by astroglia. The delay in demyelination is accompanied by a delay in the loss of mature GSTπ‐positive oligodendrocytes in Ltα−/− mice compared with wild‐type mice. Ltα−/− mice have decreased numbers of microglia at the site of insult during demyelination, although the number of astrocytes present is similar between strains. In contrast to TNFα the lack of Ltα did not alter the time course of remyelination, or the number of mature oligodendrocytes during the remyelination phase. Since Ltα is detrimental in inflammation and demyelination, but not necessary for remyelination and repair, inhibiting Ltα signaling may represent a promising strategy to treat MS.

Immune modulation by butyrophilins

The B7 family of co-stimulatory molecules has an important role in driving the activation and inhibition of immune cells. Evolving data have shown that a related family of molecules — the butyrophilins — have similar immunomodulatory functions to B7 family members and may represent a novel subset of co-stimulatory molecules. These studies have taken the field by surprise, as the butyrophilins were previously thought to only be important in lactation and milk production. In this Review, we describe the expression patterns of the various members of the butyrophilin family and explore their immunomodulatory functions. In particular, we emphasize the contribution of butyrophilins to immune homeostasis and discuss the potential of targeting these molecules for therapeutic purposes.

A CIITA-independent pathway that promotes expression of endogenous rather than exogenous peptides in immune-privileged sites.

A CIITA‐independent pathway of MHC class II expression has been found in the eye and the brain, both immune‐privileged sites. Although corneal endothelial cells were unable to express MHC class II in response to IFN‐γ alone, these cells readily expressed MHC class II molecules via a CIITA‐independent pathway when triggered by simultaneous exposure to IFN‐γ and TNF‐α. CIITA‐independent expression of MHCclass II molecules enabled corneal endothelial cells to present cytosolic, but not endosomal, ovalbumin (OVA) to OVA‐primed T cells. To determine whether CIITA‐independentexpression of MHC class II is relevant in vivo, minor H‐only‐incompatible corneal allografts prepared from CIITA knockout (KO) mice, MHC class II KO mice or wild‐type donors were placed ineyes of normal mice. Cornea allografts from wild‐type and CIITA KO mice suffered similar rejection fates, whereas far fewer class II‐deficient corneas were rejected. In addition, MHC class II‐bearing macrophages were observed in cuprizone‐induced inflammatory and demyelinating brain lesions of CIITA KO mice. We conclude that class II expression via the CIITA‐independent pathway enhances the vulnerability to rejection of corneal grafts expressing minor antigens. The potential relevance of CIITA‐independent MHC class II expression at immune‐privileged sites is discussed in relation to tolerance to strong autoantigens.