Olle Lidman

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-γ. 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.

Expression of nonclassical MHC class I (RT1‐U) in certain neuronal populations of the central nervous system

Major histocompatibility complex (MHC) class I genes consist of classical (Ia) and nonclassical (Ib) types. Recently, a set of structurally similar MHC class Ib genes in the rat, denoted RT1‐U, was described. We here demonstrate expression of RT1‐U mRNA using highly stringent oligonucleotide in situ hybridization in several different neuronal populations, including different motor nuclei and the substantia nigra in the rat MHC (c) and (n) haplotypes under normal conditions. The expression pattern for β2‐microglobulin mRNA was almost identical. In contrast, neuronal expression of classical MHC class I (RT1‐A) was low. Interestingly, after mechanical nerve injury, glial cells predominantely upregulated expression of RT1‐A, whereas neuronal expression of RT1‐U remained unchanged. Neuronal expression of nonclassical MHC class I may thus be important for immune surveillance in the nervous system.

Neurodegeneration and glial activation patterns after mechanical nerve injury are differentially regulated by non-MHC genes in congenic inbred rat strains.

Ventral root avulsion in the rat leads to a retrograde response, with activation of glia and up‐regulation of immunologic cell surface molecules such as major histocompatibility complex (MHC) antigens, and the subsequent degeneration of a large proportion of the lesioned motoneurons. Herein, we examined several inbred congenic rat strains previously known to react differently to experimentally induced autoimmune diseases and demonstrate a substantial genetic diversity in the regulation of glial activation and neuron death in this injury model. The panel of examined inbred rat strains included DA(RT1AV1), PVG.1AV1, LEW.1AV1, LEW.1N, BN(RT1N) and E3(RT1U), and the following parameters were determined: (1) MHC class II expression on glia; (2) expression of glial fibrillary acidic protein, C3 complement, and microglial response factor‐1 mRNAs in glia; (3) levels of the tumor necrosis factor‐α and interleukin‐1β cytokine mRNAs; (4) degree of motoneuron loss. The findings of considerable strain‐dependent differences in all parameters studied demonstrate important polymorphisms in the genetic regulation of these events. Furthermore, some of the studied features segregated from each other, suggesting independent regulatory mechanisms. Genes outside of the MHC complex are mainly implicated as being of importance for the phenotypic differences, as significant differences were recorded between the MHC congenic strains differing in the non‐MHC genes but not vice versa. These results contribute new important insights into the genetic regulation of glial reactivity and neuron death after mechanical nerve injuries. In addition, the finding of conspicuous strain‐dependent differences makes it necessary to consider the genetic background when designing and interpreting animal experiments involving noxious insults to the central nervous system resulting in glial activation and nerve cell loss. J. Comp. Neurol. 431:75–87, 2001.

Neuroinflammation in the rat – CNS cells and their role in the regulation of immune reactions

Summary: Recent discoveries suggest that the resident cells of the central nervous system (CNS) the nerve cells and glia, play a more immunologically active role than was previously assumed. Neuroglial communication is of central interest in virtually all types of pathological conditions that affect the brain and several features of the activation that results from nerve cell damage resemble the type of innate immune reactions that occur in other parts of the body. In particular, the characteristics of the activation of these CNS cells will affect both the interaction with cells of the immune system as well as processes related to neurodegeneration and regeneration. We here review data regarding 3 different aspects of local inflammatory activation in the rat nervous system: (i) the genetic heterogeneity of glial activation across inbred strains after nerve injury, (ii) expression of MHC class I genes in the CNS and (iii) neuroprotective effects of CNS antigen autoreactive immune reactions. Apart from neuroimmune diseases such as experimental autoimmune encephalomyelitis/multiple sclerosis, these features are also of relevance for a wider range of neurological diseases which present pathological signs of inflammation, such as Alzheimers dementia, cerebrovascular diseases and CNS trauma.

Naturally Occurring Variation in the Glutathione-S-Transferase 4 Gene Determines Neurodegeneration After Traumatic Brain Injury

AIM Genetic factors are important for outcome after traumatic brain injury (TBI), although exact knowledge of relevant genes/pathways is still lacking. We here used an unbiased approach to define differentially activated pathways between the inbred DA and PVG rat strains. The results prompted us to study further if a naturally occurring genetic variation in glutathione-S-transferase alpha 4 (Gsta4) affects the outcome after TBI. RESULTS Survival of neurons after experimental TBI is increased in PVG compared to the DA strain. Global expression profiling analysis shows the glutathione metabolism pathway to be the most regulated between the strains, with increased Gsta4 in PVG among top regulated transcripts. A congenic strain (R5) with a PVG genomic insert containing the Gsta4 gene on DA background displays a reversal of the strain pattern for Gsta4 expression and increased survival of neurons compared to DA. Gsta4 is known to effectively reduce 4-hydroxynonenal (4-HNE), a noxious by-product of lipid peroxidation. Immunostaining of 4-HNE was evident in both rat and human TBI. Intracerebral injection of 4-HNE resulted in neurodegeneration with increased levels of a marker for nerve injury in cerebrospinal fluid of DA compared to R5. INNOVATION These findings provide strong support for the notion that the inherent capability of coping with increased 4-HNE after TBI affects outcome in terms of nerve cell loss. CONCLUSION A naturally occurring variation in Gsta4 expression in rats affects neurodegeneration after TBI. Further studies are needed to explore if genetic variability in Gsta4 can be associated to outcome also in human TBI.

Vra4 congenic rats with allelic differences in the class II transactivator gene display altered susceptibility to experimental autoimmune encephalomyelitis.

Presentation of Ag bound to MHC class II (MHC II) molecules to CD4+ T cells is a key event in adaptive immune responses. Genetic differences in MHC II expression in the rat CNS were recently positioned to allelic variability in the CIITA gene (Mhc2ta), located within the Vra4 locus on rat chromosome 10. In this study, we have examined reciprocal Vra4-congenic strains on the DA and PVGav1 backgrounds, respectively. After experimental nerve injury the strain-specific MHC II expression on microglia was reversed in the congenic strains. Similar findings were obtained after intraparenchymal injection of IFN-γ in the brain. Expression of MHC class II was also lower on B cells and dendritic cells from the DA.PVGav1-Vra4- congenic strain compared with DA rats after in vitro stimulation with IFN-γ. We next explored whether Vra4 may affect the outcome of experimental autoimmune disease. In experimental autoimmune encephalomyelitis induced by immunization with myelin oligodendrocyte glycoprotein, DA.PVGav1-Vra4 rats displayed a lower disease incidence and milder disease course compared with DA, whereas both PVGav1 and PVGav1.DA-Vra4 rats were completely protected. These results demonstrate that naturally occurring allelic differences in Mhc2ta have profound effects on the quantity of MHC II expression in the CNS and on immune cells and that this genetic variability also modulates susceptibility to autoimmune neuroinflammation.

Harm or heal - divergent effects of autoimmune neuroinflammation?

The central nervous system (CNS) has been viewed as an organ that is especially sensitive to inflammatory reactions and, therefore, needs a shield in the form of ‘immune privilege’. However, recent evidence clearly demonstrates that this standpoint is, at least in part, erroneous. In the November issue of Trends in Immunology, Kipnis and Schwartz contribute a highly interesting discussion of the neuroprotective potential of autoimmune inflammation [1]. We now give our additional views on this topic. The observation that, primarily non-inflammatory insults to the CNS can lead to systemic expansion of myelin–antigen-specific autoimmune responses is not new. Thus, facial nerve trauma in the rat leads to expansion of myelin basic protein (MBP) peptide-specific T cells in draining lymph nodes [2] and similar effects are also present in humans after peripheral and central injuries [3,4]. This type of trauma-induced immune response can, under certain circumstances, be pathogenic because encephalomyelitis ensues in rat strains genetically susceptible to experimental autoimmune encephalomyelitis (EAE) [2]. Furthermore, a worsened outcome of spinal cord lesion in transgenic mice expressing MBPspecific T-cell receptors (TCRs) compared with wild-type control mice was recently demonstrated [5] and neurons die during acute EAE [6]. Collectively, these observations suggest that autoimmunity secondary to mechanical nerve lesions might promote damage. A second important notion is that of immune regulatory effects of the target tissue, where recruitment of inflammatory cells preferentially occurs in injured CNS areas [7–9]. Teleologically, these physiological autoimmune reactions could be viewed as an apt response serving to focus inflammation to injured areas and the tidying up of damaged tissue. Interestingly, however, Schwartz et al. have demonstrated beneficial and/or neuroprotective effects of CNS autoimmune reactions in several experimental models. The concept of neuroprotective autoimmunity, pioneered by this group, has also been corroborated by independent observations from other laboratories, for example, we have shown that ventral nerve root avulsion (VRA)-induced degeneration of motor-neurons is ameliorated if rats are induced to develop EAE [10]. That myelin directed autoimmune responses induced either by non-specific insults or deliberate immunization can be neuroprotective obviously has important implications for both CNS inflammatory and primarily non-inflammatory conditions, and needs to be considered in immunomodulatory treatments applied to these diseases. A major question is under what genetic and environmental circumstances particular qualities of autoimmune responses are beneficial and/or detrimental, that is, what mechanisms and/or mediators govern autoaggression versus neuroprotection. Despite years of effort, it is still unclear which functional differentiation of autoimmune T-cell responses renders them pathogenic. A Th1 cytokine bias can be disease promoting (reviewed in Ref. [11]) but certain autoimmune myelin peptide Th1 biased responses are completely non-pathogenic [12]. Schwarz and Kipnis argue that a Th1 biased immune response, somehow regulated by CD4þCD25þ regulatory cells, is an important requisite for neuroprotection [1]. We believe that this might well be the case. Additionally, circumstantial data suggest that a pure Th1 response with production of proinflammatory cytokines, such as interferon-g (IFN-g) and tumour necrosis factor-a (TNF-a), might be autoaggressive, although an additional production of neurotrophins or neuronal growth factors might render such T cells non-encephalitogenic and even neuroprotective (Fig. 1). Thus, neurotrophins are expressed in inflammatory cells in the immediate vicinity of neurons and death of motoneurons cultured in vitro in the presence of IFN-g and TNF-a is retarded by the addition of neurotrophins [10], and transfection of an encephalitogenic MBP-specific T-cell clone with a neurotrophin gene makes it nonencephalitogenic [13]. Furthermore, spinal cord trauma recruiting Th1 cells in an MBP TCR-transgenic mouse strain results in a worsened outcome compared with wild type, without evidence of increased neurotrophin production [5]. Finally, in MBP63–88 peptide induced EAE, encephalitogenic T cells using the TCRBV8S2þ display a much higher proinflammatory cytokine:neurotrophin ratio than potentially non-encephalitogenic cells bearing other TCRs [10,14]. With regard to the genetic influence, Schwartz and Kipnis state that EAE resistant strains are more resistant to CNS damage than EAE susceptible strains [1], which is not true in all situations. Using an experimental CNS damage paradigm in a variety of inbred rat strains with different EAE susceptibilities, we only found a rough correlation between EAE susceptibility and neuron death, with the EAE susceptible DA rat and the EAE resistant PVG rat strains as extremes. However, the resistant E3 rat strain developed as conspicuous neuron death as the susceptible DA rat strain [14]. The absence of an effect by in vivo depletion of T cells [16], as well as mapping of the Corresponding author: Tomas Olsson (tomas.olsson@cmm.ki.se).

Recovery from spinal cord injury differs between rat strains in a major histocompatibility complex-independent manner

Inflammation is a common characteristic of spinal cord injury. The nature of this response, whether it is beneficial or detrimental, has been the subject of debate. It has been reported that susceptibility to autoimmunity is correlated with increased functional impairment following spinal cord injury. As the ability to mount an autoimmune response has most consistently been associated with certain haplotypes of the major histocompatibility complex (MHC), we analysed the possible effects of the MHC haplotype on functional impairment and recovery following spinal cord injury. A contusion injury was induced in experimental autoimmune encephalomyelitis‐susceptible and ‐resistant rats [Dark Agouti, Lewis and Piebald Viral Glaxo (PVG), respectively]. We found that locomotion recovered significantly better in Dark Agouti rats compared with PVG and Lewis rats but an F2 intercross (PVG × PVG‐RT1av1) excluded the possibility that this difference was MHC haplotype‐dependent. Thus, we conclude that recovery following spinal cord injury is subject to considerable genetic heterogeneity that is not coupled to the MHC haplotype region. Continued research of genetic variants regulating recovery following spinal cord injury is warranted.

Facial nerve lesion response; strain differences but no involvement of IFN-γ, STAT4 or STAT6

Facial nerve lesions lead to a retrograde response characterized by activation of glia surrounding axotomized motoneurons and up-regulation of immunological cell surface molecules such as major histocompatibility complex (MHC) antigens. Cytokines, in particular interferon-&ggr;, are potent inducers of MHC expression and glial activation. We have here tested whether axotomy-induced activation is changed in transgenic mouse strains lacking components of the IFN-&ggr; signaling pathway, STAT4 or STAT6. No differences regarding astrocyte activation, ß2-microglobulin or MHC class I expression were discernible as compared to wild type controls. In contrast, there were conspicuous differences in the reaction between the examined wild type strains (C57BL/6J, BALB/c and 129/SvJ), suggesting considerable polymorphisms in the genetic regulation of these events, however, not involving IFN-&ggr;, STAT4 or STAT6.

Genetic Regulation of Nerve Avulsion-Induced Spinal Cord Inflammation

Abstract: In the animal model for multiple sclerosis (MS), experimental autoimmune encephalitis (EAE), genetic loci correlating with incidence or severity of disease are located both within and outside of the major histocompatibility complex (MHC). Whereas polymorphisms within MHC class I and II molecules are likely to be a major determinant of MHC gene influence in rat EAE, it is still unclear how non‐MHC gene regions influence disease. Genetic control of inflammation can hypothetically be either general or specific for a particular target tissue. For the latter, gene regulation of pathomechanisms in the CNS could affect reactivity of microglia or astrocytes, local cytokine/chemokine production, or even neuronal vulnerability. We have obtained strong support for this notion by observations of rat strain‐dependent variation in the inflammatory response after ventral root avulsion, a model in which mainly non‐antigen‐specific elements of the immune system promote inflammation. A comparison of strains with similar MHC haplotypes on different backgrounds and strains with different MHC haplotypes on the same background, respectively, demonstrates that the inflammatory phenotype is regulated mainly by non‐MHC genes. Interestingly, different features of the inflammatory response, such as induction of MHC class II expression, glial activation, cytokine expression, and neuronal vulnerability, varied between rat strains and were largely independent of each other. The genetic control of several basic features of inflammation in the CNS is of great relevance not only for MS/EAE, but also for several other neurological conditions with inflammatory components such as cerebrovascular and neurogenerative dieases and trauma.