Determinants of antibody-based host resistance against Pneumocystis carinii

描述（由申请方提供）：卡氏肺孢子虫（PC）肺炎是一种在全球HIV感染患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，这凸显了环境中遇到PC的频率。免疫完整的鼠宿主产生保护性免疫应答，导致亚临床感染，而SCID、CD 4 T细胞缺陷或B细胞缺陷小鼠死于PC肺炎B。然而，用PC攻击并且随后耗尽CD 4 T细胞的小鼠抵抗肺炎，这与PC特异性抗体的高滴度相关。虽然CD 4 + T细胞似乎在产生抗PC的保护性抗体中是关键的，但尚未探索记忆B细胞对保护性抗体的维持。此外，PC-免疫保护性抗体的特异性靶标尚未完全表征，特别是它们对碳水化合物表位的亲和力，最近已显示其在基于疫苗的针对其它机会性真菌病原体的抗性中是关键的。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，我们通过两个目标来进行我们的研究。具体目的I将通过在存在或不存在CD 4 + T细胞的情况下表征抗体回忆应答的动力学，评价体液介导的抗PC免疫记忆的产生。我们还将探索记忆B细胞在CD 4+非依赖性环境中激活并在SCID小鼠中重建PC免疫的潜力。特异性目标II将评估PC感染是否激发针对主要表面碳水化合物β-葡聚糖、甘露糖和几丁质的特异性抗体，以及是否针对这些表位表现出记忆抗体应答。鉴于模式识别受体dectin-1对PC β-葡聚糖的亲和力，我们将评估由dectin-1的胞外结构域与鼠IgG 1 Fc片段融合组成的抗体样免疫球蛋白是否增强了SCID小鼠中的PC清除。更好地了解肺孢子虫特异性体液免疫及其维持的决定因素将告知对这种环境病原体的抗性机制，并使我们能够在免疫缺陷宿主中最佳地接种预防PC肺炎的疫苗。PC是一种常见的环境真菌，可导致HIV+患者的致命性肺炎，人们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，以及产生抗体的细胞记住先前PC暴露的方式，从而深入了解正常宿主的抵抗力和HIV背景下疫苗设计的要求。

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.