Immune response to Pneumocystis and bone marrow failure

描述（由申请人提供）：在艾滋病患者中，由于CD 4 T细胞和I型干扰素（I型-IFN）产生的浆细胞样树突状细胞（pDC）的丢失，导致对机会性感染（如肺孢子虫肺炎（PCP））的易感性。这些感染大大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症（所有血细胞减少）。全血细胞减少症的机制知之甚少。全血细胞减少症通常发生在艾滋病的晚期。因此，失败的免疫系统和机会性感染之间可能存在直接联系。我们通过杂交IFNAR-/-和RAG-/-小鼠产生了缺乏功能性I型干扰素受体（IFNAR）以及T和B细胞的小鼠（称为IFrag-/-小鼠）。我们发现IFrag-/-小鼠中的肺孢子虫（PC）肺部感染导致由于骨髓细胞凋亡增加而导致的完全骨髓衰竭导致的快速进展的全血细胞减少症。相反，具有完整IFNAR的T和B细胞缺陷型RAG-/-小鼠在感染过程中表现出正常的造血，而淋巴细胞活性但IFNAR缺陷型IFNAR-/-小鼠在PC感染后表现出抑制的造血。用野生型脾细胞或纯化的B细胞对IFrag-/-小鼠进行免疫重建，可预防感染引起的骨髓衰竭。IFrag-/-小鼠与IFNAR-/-供体小鼠脾细胞的免疫重建仅导致PC肺感染后造血的部分拯救。IFrag- /-和RAG-/-小鼠之间的骨髓嵌合体实验显示，IFNAR表达需要在造血细胞上，而不是在基质细胞上，以便在PC肺感染期间维持造血。我们的假设是，I型-IFN，支持B细胞，维持造血过程中的压力的机会性感染，如PC感染的肺，通过影响HSC的生态位和平衡的增殖与促凋亡信号启动的全身急性期反应。为了验证这一假设，我们提出了以下具体的研究：1）确定是否缺乏I型IFN-信号通过启动促凋亡和促增殖信号之间的失衡影响骨髓微环境。2)确定B细胞维持骨髓和诱导髓外造血的机制。3)确定与RAG-/-小鼠相比，IFrag-/-小鼠的肺先天免疫应答如何改变，以及这如何决定骨髓应答。这些研究应有助于更好地理解对特定病原体的免疫应答与这些急性应激反应期间造血维持之间的联系。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。

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.