Department of Immunology and Infectious Diseases, Montana State University, Bozeman, MT 59718, USA.
J Immunol. 2011 May 15;186(10):5956-67. doi: 10.4049/jimmunol.1003558. Epub 2011 Apr 6.
We recently demonstrated that lack of type I IFN signaling (IFNAR knockout) in lymphocyte-deficient mice (IFrag(-/-)) results in bone marrow (BM) failure after Pneumocystis lung infection, whereas lymphocyte-deficient mice with intact IFNAR (RAG(-/-)) had normal hematopoiesis. In the current work, we performed studies to define further the mechanisms involved in the induction of BM failure in this system. BM chimera experiments revealed that IFNAR expression was required on BM-derived but not stroma-derived cells to prevent BM failure. Signals elicited after day 7 postinfection appeared critical in determining BM cell fate. We observed caspase-8- and caspase-9-mediated apoptotic cell death, beginning with neutrophils. Death of myeloid precursors was associated with secondary oxidative stress, and decreasing colony-forming activity in BM cell cultures. Treatment with N-acetylcysteine could slow the progression of, but not prevent, BM failure. Type I IFN signaling has previously been shown to expand the neutrophil life span and regulate the expression of some antiapoptotic factors. Quantitative RT-PCR demonstrated reduced mRNA abundance for the antiapoptotic factors BCL-2, IAP2, MCL-1, and others in BM cells from IFrag(-/-) compared with that in BM cells from RAG(-/-) mice at day 7. mRNA and protein for the proapoptotic cytokine TNF-α was increased, whereas mRNA for the growth factors G-CSF and GM-CSF was reduced. In vivo anti-TNF-α treatment improved precursor cell survival and activity in culture. Thus, we propose that lack of type I IFN signaling results in decreased resistance to inflammation-induced proapoptotic stressors and impaired replenishment by precursors after systemic responses to Pneumocystis lung infection. Our finding may have implications in understanding mechanisms underlying regenerative BM depression/failure during complex immune deficiencies such as AIDS.
我们最近证明，在淋巴细胞缺陷小鼠（IFrag(-/-)）中缺乏 I 型 IFN 信号（IFNAR 敲除）会导致肺炎球菌肺部感染后骨髓（BM）衰竭，而具有完整 IFNAR（RAG(-/-)）的淋巴细胞缺陷小鼠则具有正常的造血功能。在目前的工作中，我们进行了研究，以进一步确定该系统中诱导 BM 衰竭的机制。BM 嵌合体实验表明，IFNAR 的表达需要在 BM 衍生细胞上，但不需要在基质衍生细胞上，以防止 BM 衰竭。感染后第 7 天产生的信号似乎对决定 BM 细胞命运至关重要。我们观察到半胱天冬酶-8 和半胱天冬酶-9 介导的细胞凋亡，从中性粒细胞开始。髓系前体的死亡与继发性氧化应激有关，并与 BM 细胞培养物中的集落形成活性降低有关。用 N-乙酰半胱氨酸治疗可以减缓 BM 衰竭的进展，但不能预防。I 型 IFN 信号已被证明可以延长中性粒细胞的寿命并调节某些抗凋亡因子的表达。定量 RT-PCR 显示，与 RAG(-/-)小鼠的 BM 细胞相比，IFrag(-/-)小鼠的 BM 细胞在第 7 天的抗凋亡因子 BCL-2、IAP2、MCL-1 等的 mRNA 丰度降低。促凋亡细胞因子 TNF-α的 mRNA 和蛋白增加，而生长因子 G-CSF 和 GM-CSF 的 mRNA 减少。体内抗 TNF-α治疗可改善前体细胞在培养物中的存活和活性。因此，我们提出缺乏 I 型 IFN 信号会导致对炎症诱导的促凋亡应激的抵抗力降低，并且在对肺炎球菌肺部感染的全身反应后，前体细胞的补充受损。我们的发现可能对理解艾滋病等复杂免疫缺陷情况下再生性 BM 抑制/衰竭的机制具有重要意义。
