Molecular Basis for Overcoming Tolerance to Sm

描述（由申请人提供）：自身反应性B细胞失调与系统性红斑狼疮（SLE）有关。当B细胞耐受被克服，核抗原特异性细胞通过BCR更新信号转导导致自身抗体分泌时，疾病就发生了。了解诱导和维持B细胞无应答状态的机制对于理解SLE的分子基础至关重要。在这个应用中，我们将测试当抗原表位显示在凋亡细胞的膜泡上时，对Sm的耐受性被克服的假设。我们提出，这种独特的高度有序的膜结合表位通过BCR更新信号转导，克服了抗sm B细胞的部分能量状态。

DESCRIPTION (provided by applicant): Dysregulation of autoreactive B cells has been implicated in systemic lupus erythematosus (SLE). Disease occurs when B cell tolerance is overcome and cells specific for nuclear antigens renew signal transduction through the BCR leading to autoantibody secretion. Understanding the mechanisms that induce and maintain an unresponsive state in B cells is crucial to understanding the molecular basis of SLE. In this application we will test the hypothesis that tolerance to Sm is overcome when antigenic epitopes are displayed on the membrane blebs of apoptotic cells. We propose that this unique display of highly ordered membrane-bound epitopes overcomes a state of partial anergy in anti-Sm B cells by renewing signal transduction through the BCR. Sm-specific B cells (2-12/Vk8 Dbl) develop into mature B2 cells that exhibit an activated cell surface phenotype and fail to secrete anti-Sm antibodies in response to LPS. Interestingly, other phenotypic changes associated with anergic B cells are absent in the 2-12Nk8 Dbl B cells suggesting a state of partial anergy. In aims 1 and 2a, we will assess if the partially anergic phenotype is associated with incomplete desensitization of the BCR and if antigens displaying higher valency epitopes, such as spliceosomes, tetramers of Sm, or apoptotic membranes, are capable of renewing signal transduction. Mechanistically, renewed signal transduction may occur when desensitized receptors repartition to membrane microdomains called lipid rafts. In aim 2b we will assess if the BCR on 2-12/Vk8 Dbl B cells are excluded from lipid rafts and if these receptors are capable of translocating to the rafts upon ligation by high valency antigens. In aim 3 we will assess the effect of apoptotic cells on tolerance to Sm using an in vivo model. First, we will inject apoptotic cells into the 2-12/Vk8 Dbl mice and assess if tolerance to Sm can be overcome. In a second approach, we will introduce a defective mer gene into the 2-12/Vk8 Dbl immunoglobulin transgenic model and assess if increased levels of apoptotic cells overcome tolerance by inducing Sm-specific autoantibodies.