CONTROL OF PERSISTENT ANTIBODY RESPONSE BY FC RECEPTORS

FC 受体控制持续抗体反应

• 批准号: 6511206
• 负责人: TIMOTHY L MANSER
• 金额: $ 27.45万
• 依托单位: THOMAS JEFFERSON UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-05-15 至 2004-04-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6511206
• 关键词: B cell receptor; B lymphocyte; antibody formation; antibody receptor; biological signal transduction; dendritic cells; enzyme linked immunosorbent assay; flow cytometry; immune complex; immunologic memory; laboratory mouse; leukocyte activation /transformation; tissue /cell culture

Long-term persistence of antigen-specific antibody and the generation of highly specific memory B cells are well recognized features of the humoral immune response. The specialized microenvironment of the germinal center (GC) may be key to these pathways, in particular, the ability of the follicular dendritic cells (FDC) to retain immunogenic antigen in the form of immune complexes (ICs) for extended periods. It has been proposed that this form of antigen both drives the selection of high affinity B cell receptor somatic mutants during the primary immune response, and maintains the stability of the memory B cell compartment over extended periods thereafter. Mice deficient in the activation Fc receptors FcgammaRI and FcgammaRIII display dramatically enhanced IC deposition and retention on FDCs. However, this does not lead to perturbation of the primary immune response. In Aim 1, we propose to test the hypothesis that this enhanced IC deposition and retention on FDCs will result in elevated levels of persistent serum antibody, memory B cells, and antibody forming cells (AFCs) in the bone marrow. We will also determine whether retention of ICs on FDCs is stable to subsequent immunization with a second antigen, and whether the affinity of persistent serum antibody is lower when cognate antigen levels on FDC are higher. B cell activity during the generation and maintenance of memory may also be regulated by direct interaction of ICs with antigen specific B cells via the inhibitory FcR, FcgammaRIIB. Mice deficient in this FcR display elevated serum antibody and AFC levels after immunization, consistent with this idea and with past in vitro studies on the functioning of this FcR. However, since FcgammaRIIB is the most widely expressed FcR, found on many myeloid lineages and FDCs, this conclusion remains tentative. In Aim 2 we propose to test the hypothesis that the dysregulated expression of antibody production observed in FcgammaRIIB. deficient mice is due to absence of this FcR on B cells. Finally, recent data have shown that the mechanism of inhibition of BCR signaling upon BCR-FcgammaRIIB co-ligation is mediated by recruitment of the inositol polyphosphate phosphatase SHIP to the ITIM motif in the cytoplasmic tail of FcgammaRIIB. A mutant form of FcgammaRIIB with a Y-greater than F change in the ITIM motif, precluding the Y phosphorylation necessary for SHIP binding, does not mediate inhibition of BCR signaling in transfected cell lines. In Aim 3, we propose to test the hypothesis that the ITIM-SHIP pathway is the only FcgammaRIIB initiated pathway necessary for inhibition of B cell activity in vivo, using mice engineered to express the FcgammaRIIB Y-greater than F mutant in the B cell compartment.

抗原特异性抗体的长期持续性和高度特异性记忆B细胞的产生是体液免疫应答的公认特征。 生发中心（GC）的特殊微环境可能是这些途径的关键，特别是滤泡树突状细胞（FDC）以免疫复合物（IC）形式保留免疫原性抗原的能力。 已经提出，这种形式的抗原在初次免疫应答期间驱动高亲和力B细胞受体体细胞突变体的选择，并且在其后的延长时期内保持记忆B细胞区室的稳定性。 活化Fc受体Fc γ RI和Fc γ RIII缺陷的小鼠显示出显著增强的IC在FDC上的沉积和保留。 然而，这不会导致初始免疫应答的扰动。 在目标1中，我们提出了一个假设，即这种增强的IC沉积和保留的FDC将导致持续血清抗体，记忆B细胞，和抗体形成细胞（AFC）在骨髓中的水平升高。 我们还将确定FDC上IC的保留是否对随后用第二种抗原免疫保持稳定，以及当FDC上的同源抗原水平较高时，持久性血清抗体的亲和力是否较低。记忆产生和维持期间的B细胞活性也可以通过IC与抗原特异性B细胞经由抑制性FcR、Fc γ RIIB的直接相互作用来调节。 缺乏该FcR的小鼠在免疫后显示升高的血清抗体和AFC水平，这与该想法以及过去关于该FcR功能的体外研究一致。 然而，由于Fc γ RIIB是在许多骨髓谱系和FDC上发现的最广泛表达的FcR，因此该结论仍然是试验性的。 在目的2中，我们提出检验在Fc γ RIIB中观察到的抗体产生的失调表达的假设。缺陷型小鼠是由于B细胞上缺乏这种FcR。最后，最近的数据表明，BCR-Fc γ RIIB共连接后BCR信号传导的抑制机制是通过将肌醇多磷酸磷酸酶SHIP募集到Fc γ RIIB胞质尾区的ITIM基序介导的。 在ITIM基序中具有Y-大于F变化的Fc γ RIIB的突变形式，排除了SHIP结合所必需的Y磷酸化，在转染的细胞系中不介导BCR信号传导的抑制。 在目的3中，我们提出使用经工程改造以在B细胞区室中表达Fc γ RIIB Y-大于F突变体的小鼠来检验ITIM-SHIP途径是体内抑制B细胞活性所必需的唯一Fc γ RIIB起始途径的假设。