Adaptive immunity against Pneumocystis

描述(申请人提供)：由于肺孢子虫与艾滋病毒流行密切相关，已上升为致命性、机会性肺部感染的前线，但这种非典型真菌病原体与药物驱动的免疫抑制以及慢性肺病等慢性肺部疾病的患者越来越相关。我们最近研究了转录因子STAT4在肺免疫中的作用。我们发现，在C57BL/6背景下的STAT4-/-小鼠对P.Murina感染具有抵抗力，而在BALB/c背景上的STAT4-/-小鼠对P.Murina感染敏感(Myers等人)。提交，公共科学图书馆病原体)。令我们惊讶的是，尽管BL/6STAT4-/-和Balb/c STAT4-/-小鼠的Th1(干扰素-γ)反应较低，但它们的肺中CD4Th2(IL-4、IL-5和IL-13)反应却出人意料地受到显著损害。尽管如此，BL/6STAT4-/-，而不是Balb/c STAT4/-，小鼠保持了增强的M2巨噬细胞特征(更高的Retnla/Fizz-1mRNA表达和CCL17/TARC蛋白水平)。与肺CD4T细胞相比，BL/6STAT4-/-小鼠引流淋巴结中的CD4Th2反应增强，血清中P-Murina特异性的IgG1、IgG2b和IgG2c水平升高，而BALB/c-STAT4-/-小鼠中均未观察到这两种情况。综上所述，这些结果表明，当肺CD4T细胞应答受损时，对P.Murina的保护性免疫涉及全身性CD4Th2应答，驱动肺内最佳B细胞应答(抗体产生)和局部2型应答(IL-4/IL-13)，后者可能不是起源于CD4T细胞，推动M2巨噬细胞的发育。新的初步数据进一步支持了这一点，与未定居的艾滋病毒感染者相比，肺孢子虫感染者血浆中Th2细胞因子IL-4、IL-5和IL-13的水平显著降低，但干扰素-γ、IL-17A或IL-10的水平没有差异。在初步研究中，我们发现在肺移植后2周，C57BL/6小鼠肺组织中CD4(-)/CD49b(-)/SiglecF(-)/ICOS()先天辅助性2型细胞显著增加。提示该细胞群在感染P.Murina期间在肺部产生2型反应中可能起到作用。在其他研究中，我们使用CD19-DTR小鼠，即CD19-CRE小鼠与Cre诱导的白喉毒素受体(DTR)转基因小鼠杂交，我们发现当B细胞在P.Murina感染之前耗尽时，小鼠淋巴结中的CD4Th1和Th2反应减弱，而B细胞耗尽导致肺中CD4Th2和Th17反应增强。总而言之，我们的数据引导我们假设，2型和Th2型反应的产生介导了对肺孢子虫的保护性肺免疫。为了解决这一假设，我们提出了以下两个独立的、相互关联的目标：(1)确定在P.Murina肺部感染期间局部和系统的2型/Th2反应的发展；(2)确定B细胞在P.Murina肺部感染期间局部和系统的CD4T细胞反应发展中的作用。

DESCRIPTION (provided by applicant): Pneumocystis has risen to the forefront of lethal, opportunistic lung infections as a result of its close association with the HIV epidemic, yet this atypical fungal pathogen is becoming increasingly associated with pharmacologic-driven immunosuppression as well as patients with chronic lung diseases such as COPD. We have recently investigated the role of transcription factor STAT4 in lung immunity to P. murina. We have discovered that Stat4-/- mice on the C57BL/6 background are resistant to P. murina infection while Stat4-/- mice on the BALB/c background are susceptible (Myers et al. submitted, PLoS Pathogens). To our surprise, although having lower Th1 (IFN-y) responses, both BL/6 Stat4-/- and Balb/c Stat4-/- mice unexpectedly demonstrated significantly impaired CD4+ Th2 (IL-4, IL-5 and IL-13) responses in the lung. In spite of this, BL/6 Stat4-/-, but not Balb/c Stat4/-, mice maintained an enhanced M2 macrophage signature (higher Retnla/FIZZ-1 mRNA expression and CCL17/TARC protein levels). In contrast to lung CD4+ T cells, BL/6 Stat4-/- mice demonstrated enhanced CD4+ Th2 responses in the draining lymph nodes and enhanced P. murina-specific IgG1, IgG2b and IgG2c levels in sera, neither of which were observed in BALB/c Stat4-/- mice. Together, these results suggest that protective immunity to P. murina when lung CD4+ T cell responses are impaired involves systemic CD4+ Th2 responses driving optimal B cell responses (Ab production) and a local type 2 response (IL-4/IL-13) in the lungs, which may not be CD4+ T cell in origin, driving M2 macrophage development. This is further supported by new preliminary data showing that compared to non-colonized HIV- infected individuals, Pneumocystis-colonized HIV-infected individuals have significantly lower plasma levels of the Th2 cytokines IL-4, IL-5 and IL-13, but no difference in the levels of IFN-y, IL-17A or IL-10. In preliminary studies, we show that CD4(-)/CD49b(-)/SiglecF(-)/ICOS(+) innate helper type 2 cells were significantly increased in lung tissue of C57BL/6 mice at 2 weeks post-P. murina challenge, suggesting a potential role for this cell population in generating type 2 responses in the lung during P. murina infection. In other studies, employing CD19-DTR mice, which are CD19-Cre mice crossed with Cre-inducible diphtheria toxin receptor (DTR) transgenic mice, we found that CD4+ Th1 and Th2 responses were attenuated in the lymph nodes of mice when B cells were depleted prior to P. murina infection, yet B cell depletion resulted in enhanced CD4+ Th2 and Th17 responses in the lung. Collectively, our data leads us to hypothesize that the generation of type 2 and Th2 responses mediate protective lung immunity against Pneumocystis. To address this hypothesis, we have proposed the following two independent, interrelated Aims: (1) to define the development of local and systemic type 2/Th2 responses during P. murina lung infection and (2) define the role of B cells in the development of local and systemic CD4+ T cell responses during P. murina lung infection.