Innate Immunity and Allergy: Modulation by CTLA4

包括toll样受体（TLR） 4调节的免疫反应为适应性过敏免疫反应奠定了基础。我们的初步数据通过将TLR4激活与细胞毒性T淋巴细胞抗原4 （CTLA4）上调联系起来，揭示了肺部潜在的新型免疫途径。我们证明CTLA4信号可以抑制实验性哮喘的过敏反应。具体来说，我们发现阻断CTLA4会增加过敏性炎症，而过表达CTLA4则会抑制过敏性炎症。有两种途径扩展了这些发现。首先，先天TLR4配体在体外和体内上调CTLA4，抑制实验性哮喘；与这一观察结果一致，TLR4突变小鼠的TLR4反应不足，其过敏反应增强。其次，通过CD45RB信号增加CTLA4，降低过敏反应。由于这三种分子（CTLA4、TLR4和CD45RB）都在T调节性细胞（Tregs）上表达，我们将研究Tregs在TLR4和CD45RB介导的实验性哮喘抑制中的功能。有趣的是，我们的初步数据还显示，内毒素成分脂质A是一种TLR4配体，可以改善实验性哮喘。与我们的小鼠研究结果一致，流行病学研究表明，暴露于富含内毒素的环境可降低儿童哮喘的风险。此外，在我们的模型中，体内Treg细胞的消耗增强了过敏反应，阻断了TLR4配体介导的实验性哮喘抑制。这些观察结果表明，TLR4介导的哮喘抑制是由表达Tregs的CTLA4介导的。因此，我们的假设是TLR4通过调节CTLA4的上调来减弱适应性免疫反应，CTLA4是抑制过敏性炎症的关键途径。Aim 1将通过确定CTLA4的抑制（使用抗CTLA4抗体或缺陷小鼠）如何促进过敏性炎症，以及CTLA4表达增加如何减少过敏性炎症（使用过表达CTLA4的CTLA4转基因或CD45RB抗体）来表征CTLA4在抑制过敏性炎症中的作用。目的2将研究TLR4信号是否在体内调节CTLA4的表达。Aim 3将确定TLR4信号抑制变应性炎症的机制，包括细胞成分（APC， T细胞），以及CTLA4信号是否增强TLR4诱导的变应性炎症抑制活性。Aim 4将通过分析CTLA4启动子区域，确定TLR4和CD45RB调控CTLA4在T细胞中的表达的分子机制。该项目的目的是确定新的途径，并通过先天免疫调节过敏性哮喘潜在的治疗靶点。

The immune responses, including those modulated by Toll-like receptor (TLR) 4 set the stage for the adaptive allergic immune response. Our preliminary data have uncovered a potential novel immune pathway in the lung by linking TLR4 activation with upregulation of cytotoxic T lymphocyte antigen 4 (CTLA4). We demonstrate that CTLA4 signals can inhibit allergic responses in experimental asthma. Specifically, we show that blocking CTLA4 increases allergic inflammation, whereas over expression of CTLA4 suppresses allergic inflammation. Two pathways extend these findings. First, innate TLR4 ligands upregulate CTLA4 both in vitro and in vivo and inhibit experimental asthma; and consistent with this observation, TLR4 mutant mice, which have deficient TLR4 responses, have enhanced allergic responses. Second, increased CTLA4, by CD45RB signals, decreases allergic responses. Because all three molecules (CTLA4, TLR4, and CD45RB) are expressed on T regulatory (Tregs) cells, we will investigate the function of Tregs in the TLR4 and CD45RB mediated inhibition of experimental asthma. Interestingly, our preliminary data also show that the endotoxin component lipid A, which is a TLR4 ligand, ameliorates experimental asthma. Consistent with our murine results, epidemiological studies show that exposure to an endotoxin rich environment decreases the risk of childhood asthma. Furthermore, in our model, the depletion of Treg cells in vivo enhances allergic responses and blocks TLR4 ligand mediated inhibition of experimental asthma. These observations indicate that TLR4 mediated suppression of asthma is mediated by CTLA4 expressing Tregs. Thus, our hypothesis is that TLR4 attenuates the adaptive immune response by modulating upregulation of CTLA4, a critical pathway in the suppression of allergic inflammation. Aim 1 will characterize the role of CTLA4 in the suppression of allergic inflammation by determining how inhibition of CTLA4 (using anti-CTLA4 antibody or deficient mice) promotes allergic inflammation, and how increased CTLA4 expression decreases allergic inflammation (using CTLA4 transgenics that overexpress CTLA4, or CD45RB antibody). Aim 2 will investigate whether TLR4 signals modulate CTLA4 expression in vivo. Aim 3 will determine the mechanisms by which TLR4 signals suppress allergic inflammation, including the cellular components (APC, T cells), and whether CTLA4 signals enhance TLR4-induced suppressor activity in allergic inflammation. Aim 4 will determine the molecular mechanisms by which TLR4 and CD45RB regulate CTLA4 expression in T cells by analysis of the CTLA4 promoter region. The objective of this project is to identify novel pathways, and potential therapeutic targets by which innate immunity modulates allergic asthma.