Determinants of antibody-based host resistance against Pneumocystis carinii

描述(申请人提供)：卡氏肺孢子虫肺炎(PC)肺炎是一种在全球艾滋病毒感染者中发现的机会性感染。大多数婴儿在两岁时就会产生PC特异性抗体，这突显了PC在环境中遇到的频率。免疫完整的小鼠宿主启动保护性免疫反应，导致亚临床感染，而SCID、CD4T细胞缺陷或B细胞缺陷小鼠死于PC肺炎。然而，被PC攻击并随后耗尽CD4T细胞的小鼠抵抗肺炎，这与PC特异性抗体的高滴度有关。虽然CD4+T细胞似乎在产生针对PC的保护性抗体中起关键作用，但记忆性B细胞对保护性抗体的维持还没有被探索过。此外，PC免疫保护性抗体的特定靶点还没有完全确定，特别是它们与碳水化合物表位的亲和力，最近被证明在疫苗对其他机会性真菌病原体的抵抗力中起着关键作用。我们努力的目标是评估基于抗体的免疫可以预防PC感染的机制，我们的研究通过两个目标进行。具体目的I将通过在存在或不存在CD4+T细胞的情况下抗体回忆反应的动力学特征来评价体液介导的针对PC的免疫记忆的产生。我们还将探索记忆B细胞在非依赖于CD4+的环境中激活的潜力，并重建SCID小鼠的PC免疫。特定目标II将评估PC感染是否引起针对主要表面碳水化合物β-葡聚糖、甘露糖和甲壳素的特异性抗体，以及是否针对这些表位表现出记忆抗体反应。鉴于模式识别受体Dectin-1与PCβ-葡聚糖的亲和力，我们将评估由Dectin-1的胞外区与小鼠lgG1 Fc片段融合而成的抗体样免疫疗法是否能增强SCID小鼠的PC清除。更好地了解肺孢子虫特异性体液免疫的决定因素及其维持将有助于了解对这种环境病原体的耐药机制，并将使我们能够在免疫缺陷的宿主中最佳地接种肺炎衣原体疫苗。PC是一种常见的环境真菌，可导致HIV+患者的致命性肺炎，目前对抗体如何预防感染知之甚少。我们的研究将评估PC抗体识别的分子，以及抗体产生细胞记住以前PC暴露的方式，提供对正常宿主耐药性和HIV背景下疫苗设计要求的洞察。

DESCRIPTION (provided by applicant): Pneumocystis carinii (PC) pneumonia is an opportunistic infection found among HIV-infected patients worldwide. Most infants develop PC-specific antibodies by two years of age, underscoring the frequency at which PC is encountered environmentally. Immuno-intact murine hosts mount protective immune responses leading to subclinical infection, while SCID, CD4 T cell deficient, or B cell deficient mice succumb to PC pneumonia. Yet, mice challenged with PC and thereafter depleted of CD4 T cells resist pneumonia, correlating with high titers of PC specific antibody. While CD4+ T cells appear to be critical in the generation of protective antibodies against PC, maintenance of protective antibodies by memory B cells has not been explored. Further, the specific targets of PC-immunoprotective antibodies have not been fully characterized, particularly their affinity for carbohydrate epitopes, which have recently been shown to be critical in vaccine-based resistance against other opportunistic fungal pathogens. The goal of our efforts is to evaluate the mechanisms whereby antibody based immunity may prevent PC infection, and we approach our studies through two aims. Specific Aim I will evaluate the generation of humoral-mediated immunologic memory against PC through characterization of the kinetics of antibody recall responses in the presence or absence of CD4+ T cells. We will also explore the potential of memory B cells to activate in a CD4+ independent environment and reconstitute PC immunity in SCID mice. Specific Aim II will evaluate whether PC infection elicits specific antibodies against the major surface carbohydrates beta-glucan, mannose, and chitin, and whether memory antibody responses are manifested against these epitopes. Given the affinity of the pattern recognition receptor dectin-1 for PC beta-glucan, we will evaluate whether an antibody-like immunotherapeutic consisting of the extracellular domain of dectin-1 fused to the murine lgG1 Fc fragment enhances PC clearance in SCID mice. Greater understanding of the determinants underlying Pneumocystis-specific humoral immunity and its maintenance will inform on resistance mechanisms against this environmental pathogen and will allow us to optimally vaccinate against PC pneumonia in immunodeficient hosts. PC is a commonly encountered environmental fungus causing lethal pneumonia in HIV+ patients, and little is understood as to how antibodies may prevent infection. Our studies will evaluate the molecules that PC antibodies recognize, and the manner whereby antibody-producing cells remember previous PC exposures, providing insight into normal host resistance and the requirements for vaccine design in the setting of HIV.