B细胞介导的肺纵隔淋巴结结构重塑在结核感染免疫中的作用机制

Lung mediastinal lymph nodes, the major site of pathogen trapping and T cell priming, have largely been overlooked during Mycobacterium tuberculosis infection. We have recently observed that Mtb infection leads to a profound and persistent alternation of the architecture, composition and cellularity of the lymph nodes in the infected mice. This tissue alteration is characterized by an unproportional expansion of B cell compartment and emergence of Mtb-specific Th1 cells that also display the molecules commonly associated by T follicular helper (Tfh) cells. Significantly, B cell depletion decreases pathogen loads and Ag-specific T cell numbers at the site. Theses observations suggest a previously unappreciated host-pathogen standoff in lymph nodes, centred on the role of B cells in the infection and immunity in the secondary lymphoid tissue. We hypothesize that: B cell-mediated re-structure of lymph nodes promotes Mtb dissemination and subsequent development of CD4 T effectors capable of surveying B cell enriched lesions is one host mechanism for restraining mycobacterial growth at the site. In this study, we will examine following specific aims: To determine the mechanisms underlying lymphoid alteration and B cell-dependent Mtb dissemination in mice and To define the mechanisms that regulate CD4+ T cell effector functions in Mtb-infected lymph nodes. Our proposed this study will lead to a deeper understanding of tissue-specific immunity and mechanisms underlying pathogenesis of mycobacterial diseases.

肺纵隔淋巴结是宿主捕获病原菌和T细胞启动的主要组织，然而其在结核菌感染过程中的作用机制并不明确。我们前期研究发现，结核菌感染导致小鼠淋巴结中B细胞不成比例地大量增殖，同时产生了结核菌抗原特异性Th1细胞，这些细胞具有Tfh的特性；另外，耗竭 B细胞可以显著降低淋巴结中细菌载量和Tfh细胞的数量，而耗竭CD4 T细胞，淋巴结中的B细胞并没有受到影响，表明淋巴结中Tfh的产生依赖于B细胞。基于此，我们提出B细胞介导的淋巴结重塑可促进细菌传播，而随后产生抗原特异性Tfh是宿主抑制结核菌在淋巴结中增殖的假说。本项目拟在前期的基础上，通过多色免疫组化技术和小鼠骨髓细胞过继转移等，进一步研究结核菌感染后小鼠B细胞介导的淋巴组织重塑和结核菌传播的机制以及淋巴结Tfh细胞的功能及其作用机制。项目完成，将加深我们对淋巴结在结核病发生中的作用机制的理解，为结核病免疫干预、疫苗研发和治疗提供新的思路和可能靶点。

肺纵隔淋巴结（LN）是宿主捕获病原菌和T细胞启动的主要组织，然而其在结核菌感染过程中的作用机制并不明确。在本项目中，我们发现结核分枝杆菌感染通过增加B细胞的数量和皮质旁易位来重塑LN结构。皮质旁B淋巴细胞和CD35+滤泡树突状细胞簇的形成分散了产生CCL21的成纤维网状细胞，并将含有病原体的髓细胞与抗原特异性CD4+T细胞分离。B细胞的耗竭恢复了慢性感染小鼠的趋化因子和淋巴结构，并减少了LNs中的细菌负荷。重要的是，在慢性结核感染期间，这种重塑过程损害了初始CD4+T细胞对分枝杆菌和无关抗原的反应。同时，我们也观察到在LN中产生了结核菌抗原特异性Th1细胞，这些细胞具有Tfh的特性；条件性敲除BCL6发现，BCL6对结核菌感染急性期没有明显的保护作用，然而对于感染的慢性期是必须的。我们的研究揭示了炎症过程中LN微观的调节机制，并确定B细胞是限制LN中T细胞对持续性细胞内感染反应的关键因素。