Isotype specific regulation of lg class switching

描述(申请人提供)：B细胞在被抗原激活后，经历抗体类型(同型)的转换，从表达IgM转变为表达Ig G、Ig A或Ig E，同时保持对同一抗原的特异性。由于同种类型决定了抗体的效应器功能，因此类别转换允许体液免疫反应对不同的感染性生物做出适应性反应。类转换是通过位于每个重链恒定(CH)区基因上游的开关(S)区序列之间的DNA重组事件发生的。许多研究(包括本实验室的许多研究)已经证实，特定的未重排CH基因的转录发生在切换之前，并且这种转录是切换所必需的。然而，最近的数据表明，开关重组的同型特异性在其他未确定的水平上受到调节。免疫球蛋白A转换的调节尤其神秘，因为它只能在培养中诱导到低水平，但却是体内含量最丰富的抗体类别，特异性地在粘膜组织中表达。免疫球蛋白是抵御病原体通过体孔进入的重要第一道防线。我们实验室的数据表明，Lsf/Cp2/LBP-1c结合了与Ig A CH基因相关的转换区(S)DNA序列，并调节了1.29u B细胞系向Ig A的转换。我们还发现，组蛋白甲基转移酶SUV39H1特异性地增加了质粒开关底物中的IgA开关。本研究的目的是研究这一调控机制，并为染色质可及性和S特定区域的组蛋白修饰调控类开关重组的假说提供证据。在目标1中，我们建议研究SUV39H1在内源性开关重组中的作用及其作用机制。我们将调查SUV39H1抑制序列特异性DNA结合蛋白的活性以抑制向IgA的开关重组的假设。这种抑制蛋白最有可能的候选者是LSF/CP-2/LBP-1c，它已知与组蛋白脱乙酰酶和多色素基团蛋白结合。目的2确定LSF是否特异性地抑制正常脾B细胞中的IgA开关重组，并探讨LSF抑制IgA开关的机制。

DESCRIPTION (provided by applicant): Upon activation by antigen, B cells undergo antibody class (isotype) switching, changing from expression of IgM to expression of IgG, IgA or IgE, while maintaining specificity for the same antigen. Since the isotype determines the effector function of the antibody, class switching allows the humoral immune response to adaptively respond to different infectious organisms. Class switching occurs by a DNA recombination event between switch (S) region sequences located upstream of each heavy chain constant (Ch) region gene. Numerous studies (including many from this laboratory) have established that transcription of specific unrearranged Ch genes occurs prior to switching and that this transcription is required for switching. Recent data, however, indicate that isotype specificity of switch recombination is regulated at additional undefined levels. Regulation of IgA switching is especially mysterious because it can only be induced to low levels in culture and yet is the most abundant antibody class in the body, expressed specifically in mucosal tissues. IgA is an important first line of defense against pathogens entering through body orifices. Data from our lab indicate that LSF/CP2/LBP-1c binds the switch (S) region DNA sequences associated with the IgA Ch gene and regulates switching to IgA in the l.29u B cell line. We have also found that the histone methyltransferase Suv39h1 specifically increases IgA switching in a plasmid switch substrate. The goal of this proposal is to investigate the mechanism of this regulation and to provide evidence for the hypothesis that chromatin accessibility and histone modifications of specific S regions regulate class switch recombination. In Aim 1 we propose to investigate the role of Suv39h1 in endogenous switch recombination and the mechanism of its function. We will investigate the hypothesis that Suv39h1 inhibits the activity of a sequence-specific DNA binding protein to repress switch recombination to IgA. The most likely candidate for this inhibitory protein is LSF/CP-2/LBP-1c, which is known to bind histone deacetylases and polychrome group proteins. Aim 2 will be to determine whether LSF specifically inhibits IgA switch recombination in normal splenic B cells and to examine the mechanism of inhibition of IgA switching by LSF.