Immune response to Pneumocystis and bone marrow failure

描述(申请人提供)：艾滋病患者易受机会性感染，如肺孢子虫肺炎(PCP)，由于失去了CD4T细胞和产生浆细胞样树突状细胞(PDC)的I型干扰素(I型干扰素)。这些感染极大地增加了发病率和死亡率。艾滋病的另一个看似独立的问题是由于再生骨髓衰竭而导致的进行性全血细胞减少(所有血细胞减少)。全血细胞减少的机制还知之甚少。全血细胞减少症通常发生在艾滋病的晚期。因此，免疫系统衰竭和机会性感染之间可能存在直接联系。我们通过与IFNAR-/-和RAG-/-小鼠杂交，产生了同时缺乏功能性I型干扰素受体(IFNAR)和T和B细胞的小鼠(称为IFRAG-/-小鼠)。我们发现，在IFRAG-/-小鼠中，肺孢子虫(PC)的肺部感染导致快速进行性的全血细胞减少，这是由于骨髓细胞凋亡增加而导致的完全骨髓衰竭。相反，具有完整IFNAR的T和B细胞缺陷RAG-/-小鼠在感染过程中表现出正常的造血功能，而IFNAR-/-小鼠在PC感染后表现出抑制的造血功能。用野生型脾细胞或纯化的B细胞进行IFRAG-/-小鼠的免疫重建可以防止骨髓衰竭对感染的反应。用来自IFNAR-/-供者小鼠的脾细胞对IFRAG-/-小鼠进行免疫重建，仅能部分挽救PC肺部感染后的造血。IFRAG-/-和RAG-/-小鼠之间的骨髓嵌合实验表明，在PC肺部感染期间，造血细胞上需要表达IFNAR，但基质细胞上不需要表达IFNAR。我们的假设是，在B细胞的支持下，I型IFN通过影响HSC的生态位，在机会性感染(如肺部PC感染)的压力下维持造血，并平衡由全身急性时相反应启动的增殖和促凋亡信号。为了验证这一假设，我们提出了以下具体研究：1)确定I型干扰素信号的缺乏是否通过启动促凋亡和促增殖信号之间的失衡来影响骨髓微环境。2)确定B细胞维持髓质和诱导髓外造血的机制。3)确定与RAG-/-小鼠相比，IFRAG-/-小鼠肺部的先天免疫反应是如何改变的，以及这可能如何决定骨髓反应。这些研究应该有助于更好地理解在这些急性应激反应中对特定病原体的免疫反应与维持造血之间的联系。这可能会对艾滋病等复杂免疫缺陷期间全血细胞减少症的治疗产生影响。公共卫生相关性：我们的建议是研究在肺孢子虫肺炎的压力下，I型干扰素系统和获得性免疫系统如何支持造血(血细胞产生)。在艾滋病的过程中，患者遭受反复感染，如肺孢子虫肺炎以及全血细胞减少症，这是一种广泛的血液细胞成分缺陷。我们的小鼠模型将在这项拟议的拨款中得到进一步发展，证明在肺孢子虫的压力下，I型干扰素系统和获得性免疫系统的丧失会导致由于骨髓衰竭而导致的全血细胞减少。需要了解免疫系统如何支持造血，以制定预防和治疗艾滋病患者全血细胞减少症的策略。

DESCRIPTION (provided by applicant): In AIDS patients' susceptibility to opportunistic infections, such as Pneumocystis Pneumonia (PCP), occurs due to the loss of CD4 T cells and type I interferon (type-I-IFN) producing plasmacytoid dendritic cell (pDC). These infections contribute greatly to morbidity and mortality. An additional and seemingly independent problem in AIDS is the occurrence of progressive pancytopenia (reduction of all blood cells) due to regenerative bone marrow failure. Mechanisms of pancytopenia are poorly understood. Pancytopenia commonly occurs during later stages of AIDS. Therefore, a direct link between the failing immune system and opportunistic infections may exist. We generated mice lacking both a functional type-I-interferon receptor (IFNAR) and T and B cells (referred to as IFrag-/- mice) by crossing IFNAR-/- and RAG-/- mice. We found that Pneumocystis (PC) lung infection in IFrag-/- mice results in a rapidly progressing pancytopenia due to complete bone marrow failure due to increased bone marrow cell apoptosis. In contrast T and B cell deficient RAG-/- mice with intact IFNAR demonstrated normal hematopoiesis during the course of infection and lymphocyte-competent but IFNAR- deficient IFNAR-/- mice showed depressed hematopoiesis in response to PC infection. Immune reconstitution of IFrag-/- mice with wildtype splenocytes or purified B cells prevented bone marrow failure in response to the infection. Immune reconstitution of IFrag-/- mice with splenocytes from IFNAR-/- donor mice resulted in only partial rescue of hematopoiesis following PC lung infection. Bone marrow chimera experiments between IFrag- /- and RAG-/- mice revealed that IFNAR expression is required on hematopoietic cells but not on stromal cells in order to maintain hematopoiesis during PC lung infection. Our hypothesis is that type-I-IFNs, supported by B cells, maintain hematopoiesis during the pressure of opportunistic infections such as PC infection of the lung by affecting the HSC niche and balance proliferative versus pro-apoptotic signals initiated by the systemic acute phase response. To validate this hypothesis, we propose the following specific studies: 1) Determine whether the lack of type I IFN-signaling affects the bone marrow microenvironment by initiating a misbalance between pro-apoptotic and pro-proliferative signals. 2) Determine the mechanisms by which B cells act to maintain medullar and induce extra-medullar hematopoiesis. 3) Determine how the innate immune response of the lung is altered in IFrag-/- mice compared to RAG-/- mice and how this may determine the bone marrow response These studies should lead to a better understanding between connections of immune responses to specific pathogens and maintenance of hematopoiesis during these acute stress responses. This may have implications in the management of pancytopenia during complex immunodeficiencies such as AIDS. PUBLIC HEALTH RELEVANCE: Our proposal is to study how the type-I-interferon system and the acquired immune system support hematopoiesis (blood cell production) when under the stress of Pneumocystis pneumonia. During the course of AIDS, patients suffer from recurrent infections such as Pneumocystis pneumonia as well as pancytopenia, a broad deficiency of all blood cell components. Our mouse model would be further developed in this proposed grant demonstrating loss of the type-I-interferon system and acquired immune system resulting in pancytopenia due to bone marrow failure, when under the stress of Pneumocystis. Understanding how the immune system supports hematopoiesis is needed to develop strategies for the prevention and treatment of pancytopenia in AIDS patients.