Immune response to Pneumocystis and bone marrow failure

描述（由申请人提供）：艾滋病患者对机会性感染的易感性，如肺囊虫肺炎（PCP），是由于CD4 T细胞和I型干扰素（I- ifn）产生浆细胞样树突状细胞（pDC）的损失而发生的。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发生进行性全血细胞减少（所有血细胞减少）。全细胞减少症的机制尚不清楚。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。我们通过将IFNAR-/-和RAG-/-小鼠杂交，产生了既缺乏功能性i型干扰素受体（IFNAR）又缺乏T细胞和B细胞的小鼠（称为IFrag-/-小鼠）。我们发现肺囊虫（PC）肺部感染IFrag-/-小鼠，由于骨髓细胞凋亡增加导致骨髓完全衰竭，导致全血细胞减少症迅速进展。相比之下，具有完整IFNAR的T细胞和B细胞缺陷的RAG-/-小鼠在感染过程中表现出正常的造血功能和淋巴细胞能力，但IFNAR-缺陷的IFNAR-/-小鼠在PC感染时表现出造血功能抑制。用野生型脾细胞或纯化的B细胞对IFrag-/-小鼠进行免疫重建，可防止对感染的骨髓衰竭。用IFNAR-/-供体小鼠的脾细胞对IFrag-/-小鼠进行免疫重建后，PC肺感染后只能部分恢复造血功能。IFrag- /-和RAG-/-小鼠骨髓嵌合体实验显示，在PC肺感染期间，IFNAR在造血细胞上表达，而在基质细胞上不表达，以维持造血功能。我们的假设是，在B细胞的支持下，i型ifn通过影响HSC生态位，在机会性感染（如肺PC感染）的压力下维持造血功能，并平衡由全身急性期反应引发的增殖与促凋亡信号。为了验证这一假设，我们提出以下具体研究：1)确定I型ifn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细胞维持髓质造血和诱导髓外造血的机制。3)确定与RAG-/-小鼠相比，IFrag-/-小鼠肺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。这些研究将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。这可能对复杂免疫缺陷（如艾滋病）期间全血细胞减少症的管理有影响。公共卫生相关性：我们的建议是研究i型干扰素系统和获得性免疫系统在肺囊虫肺炎应激下如何支持造血（血细胞生成）。在艾滋病病程中，患者会反复感染，如肺囊虫性肺炎和全血细胞减少症，即所有血细胞成分普遍缺乏。我们的小鼠模型将在本次拨款中进一步发展，证明在肺囊虫病的压力下，i型干扰素系统和获得性免疫系统的丧失导致骨髓衰竭导致全血细胞减少。了解免疫系统如何支持造血是需要制定策略预防和治疗艾滋病患者全血细胞减少症。

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.