Cathepsin B-Deficient Mice Resolve Leishmania major Inflammation Faster in a T Cell-Dependent Manner

A critical role for intracellular TLR9 has been described in recognition and host resistance to Leishmania parasites. As TLR9 requires endolysosomal proteolytic cleavage to achieve signaling functionality, we investigated the contribution of different proteases like asparagine endopeptidase (AEP) or cysteine protease cathepsins B (CatB), L (CatL) and S (CatS) to host resistance during Leishmania major (L. major) infection in C57BL/6 (WT) mice and whether they would impact on TLR9 signaling. Unlike TLR9-/-, which are more susceptible to infection, AEP-/-, CatL-/- and CatS-/- mice are as resistant to L. major infection as WT mice, suggesting that these proteases are not individually involved in TLR9 processing. Interestingly, we observed that CatB-/- mice resolve L. major lesions significantly faster than WT mice, however we did not find evidence for an involvement of CatB on either TLR9-dependent or independent cytokine responses of dendritic cells and macrophages or in the innate immune response to L. major infection. We also found no difference in antigen presenting capacity. We observed a more precocious development of T helper 1 responses accompanied by a faster decline of inflammation, resulting in resolution of footpad inflammation, reduced IFNγ levels and decreased parasite burden. Adoptive transfer experiments into alymphoid RAG2-/-γc-/- mice allowed us to identify CD3+ T cells as responsible for the immune advantage of CatB-/- mice towards L. major. In vitro data confirmed the T cell intrinsic differences between CatB-/- mice and WT. Our study brings forth a yet unappreciated role for CatB in regulating T cell responses during L. major infection.细胞内Toll样受体9（TLR9）在利什曼原虫的识别以及宿主抗该病原体感染过程中的关键作用已有相关报道。鉴于TLR9需经内溶体蛋白水解切割才能实现信号转导功能，本研究针对C57BL/6野生型（WT）小鼠在感染硕大利什曼原虫（L. major）过程中，诸如天冬酰胺内肽酶（AEP）以及半胱氨酸蛋白酶家族的组织蛋白酶B（CatB）、L（CatL）与S（CatS）等不同蛋白酶对宿主抗性的贡献，以及这些蛋白酶是否会影响TLR9信号通路展开了探究。TLR9基因敲除（TLR9-/-）小鼠的感染易感性更高，而AEP基因敲除、CatL基因敲除及CatS基因敲除小鼠的抗感染能力与野生型小鼠相当，提示这些蛋白酶并非单独参与TLR9的加工过程。有趣的是，我们观察到CatB基因敲除小鼠的硕大利什曼原虫感染相关皮损消退速度显著快于野生型小鼠，但未发现CatB参与树突状细胞与巨噬细胞的TLR9依赖型或非依赖型细胞因子应答，亦或在抗硕大利什曼原虫感染的天然免疫应答中发挥作用的证据。我们同样未检测到抗原呈递功能存在差异。研究发现，辅助性T细胞1（Th1）应答更早出现，伴随炎症反应更快消退，最终实现足垫炎症消退、干扰素γ（IFNγ）水平降低以及寄生虫负荷减少。向无淋巴细胞的RAG2敲除γc链敲除（RAG2-/-γc-/-）小鼠进行过继转移实验，使我们明确了CD3阳性T细胞是CatB基因敲除小鼠相较于野生型小鼠具备硕大利什曼原虫抗感染免疫优势的关键因素。体外实验数据证实了CatB基因敲除小鼠与野生型小鼠之间存在T细胞固有差异。本研究揭示了组织蛋白酶B在硕大利什曼原虫感染过程中调控T细胞应答的此前未被认知的作用。