Expression of Scavenger receptor A on antigen presenting cells is important for CD4+ T-cells proliferation in EAE mouse model

Levy-Barazany and Frenkel Journal of Neuroinflammation 2012, 9:120 http://www.jneuroinflammation.com/content/9/1/120 RESEARCH JOURNAL OF NEUROINFLAMMATION Open Access Expression of Scavenger receptor A on antigen presenting cells is important for CD4+ T-cells proliferation in EAE mouse model Hilit Levy-Barazany and Dan Frenkel* Abstract Background: Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) characterized by damage to the neuronal myelin sheath. One of the key effectors for inflammatory injury is the antigenpresenting cell (APC). The class A scavenger receptor (SRA), constitutively expressed by APCs, such as macrophages and dendritic cells in peripheral tissues and the CNS, was shown to play a role in the phagocytosis of myelin; however, the role of SRA in the development of experimental autoimmune encephalomyelitis (EAE) and autoimmune reaction in the periphery has not yet been studied. Methods: We investigated EAE progression in wild-type (WT) vs. SRA−/− mice using clinical score measurements and characterized CNS pathology using staining. Furthermore, we assessed SRA role in mediating anti myelin proinflammatory response in cell cultures. Results: We discovered that EAE progression and CNS demyelination were significantly reduced in SRA−/− mice compared to WT mice. In addition, there was a reduction of infiltrating peripheral immune cells, such as T cells and macrophages, in the CNS lesion of SRA−/− mice, which was associated with reduced astrogliosis. Immunological assessment showed that SRA deficiency resulted in significant reduction of pro-inflammatory cytokines that play a major role in EAE progression, such as IL-2, IFN-gamma, IL-17 and IL-6. Furthermore, we discovered that SRA−/− APCs showed impairments in activation and in their ability to induce pro-inflammatory CD4+ T cell proliferation. Conclusion: Expression of SRA on APCs is important for CD4+ T-cells proliferation in EAE mouse model. Further studies of SRA-mediated cellular pathways in APCs may offer useful insights into the development of MS and other autoimmune diseases, providing future avenues for therapeutic intervention. Keywords: Scavenger receptor A, SRA, CD4+ T-cell, EAE, Multiple sclerosis, Macrophage, APC, Microglia, Astrocyte Introduction Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system (CNS) characterized by the formation of focal demyelinating plaques in the brain and spinal cord [1-3]. Understanding the mechanisms leading to cumulative neurological disability in MS and developing effective therapeutic strategies to reduce disease progression are major goals in MS research [4-6]. Scavenger receptor A (SRA), also known as CD204, is a trimeric type II transmembrane glycoprotein expressed as two functional splice variants, SRA-I and SRA-II. SRA is * Correspondence: Department of Neurobiology, George S. Wise Faculty of Life Sciences, Sherman Building, Room 424, Tel Aviv 69978, Israel constitutively expressed by mononuclear phagocytes, such as macrophages, dendritic cells (DCs), and Kupffer cells in peripheral tissues, and by microglia in the CNS [7,8]. The scavenger receptors have been demonstrated to play an important role in innate immune defense against pathogens by acting as pattern recognition receptors (PRRs) [9]. PRRs are capable of binding a broad range of ligands, including bacterial surface components, chemically modified and endogenous danger molecules released from damaged cells [10]. Recently, it was shown by Cotena et al. [11] that SRA could ensure an inflammatory response of the appropriate magnitude via modulation of the activities of pro-inflammatory receptors and production of chemokines. This suggests that © 2012 Levy-Barazany and Frenkel; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Levy-Barazany and Frenkel Journal of Neuroinflammation 2012, 9:120 http://www.jneuroinflammation.com/content/9/1/120 Page 2 of 8 SRA might regulate inflammation via macrophage function and consequent in tissue remodeling in pathological conditions. Furthermore, it was shown that SRA deficiency might cause impairment of infarct remodeling, which results in cardiac rupture via insufficient production of interleukin (IL)-10 and enhanced expression of tumor necrosis factor (TNF)α. This suggests that SRA might contribute to the prevention of cardiac rupture after injury [12]. It was reported that SRA, expressed on microglia and macrophages, plays a role in mediating clearance of neurotoxic β-amyloid plaques in CNS tissues in Alzheimer’s disease animal models [13,14]. Along with other receptors of the SR family, such as class B2 scavenger receptors or CD36 [15], RAGE [16] and others [17]. Furthermore, it was found that the expression of these microglial Aβ phagocytic receptors decreased significantly in transgenic AD mice and, thereby, promoted Aβ accumulation and contributed to neurodegeneration [18]. In approximately 85% of cases, MS patients experience a relapsing-remitting form of disease, which is characterized by acute inflammatory demyelinating episodes, and followed by decreased inflammation and partial remyelination. The process of remyelination is insufficient in this disease, and the accumulated load of lesions that fail to remyelinate results in an eventual secondary progressive neurological state [19-21]. Reports using cell culture systems suggested that phagocytosis of myelin by microglia is mediated by SRA and that this process could result in beneficial remyelination, leading to regeneration of axons in the CNS [22-24]. The experimental autoimmune encephalomyelitis (EAE) mouse model is commonly used to study disease pathogenesis and to test new therapeutic approaches. In this model, mice are immunized with myelin antigen and develop different levels of paralysis that can be monitored [25]. Impairment in remyelination was found to accelerate disease progression in the EAE mouse model [26]. Therefore, we hypothesized that SRA deficiency will exacerbate disease progression in the EAE mouse model. emulsion containing 250 μg of MOG35–55 peptide (MEVGWYRSPFSRVVHLYRNGK) and 400 μg of Mycobacterium tuberculosis extract H37 Ra (BD Biosciences, Austin, TX, USA) in incomplete Freund’s adjuvant oil. In addition, the animals received intraperitoneal injection of 250 ng of pertussis toxin (List Biological Laboratories, Campbell, CA, USA). on Day 0 and Day 2. Clinical signs of EAE were assessed according to the following score: 0, no disease; 1, loss of tone in the tail; 2, hind limb weakness; 3, hind limb paralysis; 4, hind limb plus forelimb paralysis; 5, moribund state. Methods Animals WT female mice, and mice that are deficient in type I and type II (...truncated)