Integrin CD11b and its role in immune suppression

描述(申请人提供)：口服诱导免疫耐受(口服耐受)因其特异性和持久的免疫抑制而在临床应用中具有巨大的潜力，如类风湿性关节炎。然而，目前以口服耐受为基础的治疗效果较低，这阻碍了其在人类患者中的实际应用。因此，我们的长期目标是确定口服耐受介导的免疫抑制的分子和细胞过程。最近的研究表明，口服耐受的形成依赖于抗原提呈细胞(APC)，包括CD11b+CD11c-巨噬细胞和CD11c+树突状细胞(DC)，也依赖于表达转录因子Foxp3的独特的CD4+CD25+T调节细胞(Treg)群体的形成。体内已鉴定出两种不同的Foxp3+Treg细胞亚型：自然产生的Treg细胞(NTreg)和适应性/诱导的Treg细胞(ITreg)。在这一应用中，我们建议研究整合素CD11b/CD18(Mac-1，1M22)，一种在巨噬细胞和DC上高表达的受体，如何促进口服耐受的建立。我们的初步结果表明，在口服耐受诱导条件下，CD11b的基因失活不会影响免疫激活、DC分化或CD4+CD25+Foxp3+Treg细胞总数；但它完全取消了抗原诱导的口服耐受。我们发现，小鼠CD11b/CD18缺陷会导致IL-6表达增强，并优先偏向Th17，Th17是一种独特的T细胞谱系，其特征是产生大量IL-17。此外，过继转移CD11b+CD11c-巨噬细胞而不是CD11c+DC可以恢复CD11b-/-小鼠的口服耐受。基于这些发现，我们假设CD11b通过抑制Th17分化促进口服耐受的发展。我们计划在两个具体目标上检验我们的假设。首先，鉴于最近的报告显示口服耐受不需要nTreg细胞，我们将使用CD11b-/-OTIIRag1-/-小鼠和Foxp3(GFP)OTIIRag1/-转基因小鼠来验证我们的假设，即CD11b缺陷专门影响Foxp3+iTreg细胞的生成或功能，这将使我们能够更好地监测口服耐受诱导条件下外周淋巴器官中iTreg细胞的生成和功能。在特定的目标2中，我们将使用针对IL-6和IL-6受体的功能阻断抗体以及IL-6-/-小鼠，验证CD11b缺陷通过增加粘膜巨噬细胞产生IL-6来消除口服耐受性的假设。鉴于口服耐受在治疗各种自身免疫性疾病中的潜力，该项目产生的信息不仅将帮助我们更好地了解免疫耐受的生物学，还可能为我们提供更好的策略，以提高基于口服耐受的治疗效果。 公共卫生相关性：这项研究的完成将通过调节Treg和Th17分化之间的平衡，为整合素CD11b在口腔耐受发展中的独特作用提供新的见解。考虑到Th17细胞与人类患者各种自身免疫性疾病之间的强烈关联，产生的信息也可能帮助我们设计更好的基于口服耐受的方案，这些方案可以用于治疗自身免疫性疾病的临床应用。

DESCRIPTION (provided by applicant): Orally-induced immune tolerance (oral tolerance) has great potential in clinical applications, such as rheumatoid arthritis, owing to its specific and long-lasting immune suppression. However, the current oral tolerance-based therapy suffers from low therapeutic efficacy, which prevents it from actual use in human patients. Thus, our long term goal is to determine the molecular and cellular processes underlying oral tolerance-mediated immune suppression. Recent studies demonstrate that the development of oral tolerance is dependent on antigen-presenting cells (APC), including CD11b+CD11c- macrophages and CD11c+ dendritic cells (DC), and also on the formation of a distinct CD4+CD25+ T regulatory (Treg) cell population that expresses the transcription factor Foxp3. Two distinct subtypes of Foxp3+ Treg cells have been identified in vivo: the naturally occurring Treg cells (nTreg) and the adaptive/induced Treg cells (iTreg). In this application, we propose to study how integrin CD11b/CD18 (Mac-1, 1M22), a receptor that is highly expressed on macrophages and DC, facilitates the establishment of oral tolerance. Our preliminary results demonstrate that genetic inactivation of CD11b does not affect immune activation, DC differentiation, or the number of total CD4+CD25+Foxp3+ Treg cells under oral tolerance-inducing conditions; but it completely abolishes antigen- induced oral tolerance. We show that deficiency of CD11b/CD18 in mice leads to enhanced expression of IL-6 and preferential immune deviation toward Th17, a distinct T cell lineage characterized by the production of large quantities of IL-17. In addition, we show that adoptive transfer of CD11b+CD11c- macrophages but not CD11c+ DC could restore the defective oral tolerance in CD11b-/- mice. Based on these discoveries, we hypothesize that CD11b facilitates the development of oral tolerance by suppressing Th17 differentiation. We plan to test our hypothesis in two specific aims. First, in light of the recent report showing that nTreg cells are not required for oral tolerance, we will test our hypothesis that CD11b deficiency specifically affects the generation or function of Foxp3+ iTreg cells, using CD11b-/-OTIIRag1-/- mice and Foxp3(gfp)OTIIRag1-/- transgenic mice, which will enable us to better monitor the generation and function of iTreg cells in the peripheral lymphoid organs under oral tolerance inducing conditions. In Specific Aim 2, we will test the hypothesis that CD11b deficiency abrogates oral tolerance by enhancing IL-6 production by mucosal macrophages, using function-blocking antibodies against IL-6 and IL-6 receptor, as well as IL-6-/- mice. Given the potential of oral tolerance in the treatment of various autoimmune diseases, the information generated from this project will not only helps us better understand the biology of immune tolerance, it may also offer us better strategies to enhance the therapeutic efficacy of oral tolerance-based therapies. PUBLIC HEALTH RELEVANCE: Completion of this study will provide novel insights into the unique role of integrin CD11b in the development of oral tolerance by regulating the balance between Treg and Th17 differentiation. Given the strong association between Th17 cells and various autoimmune diseases in human patients, the information generated may also help us design better oral-tolerance-based regimens that can be used in clinical applications for the treatment of autoimmune diseases.