Rocha-Perugini Vera, Martínez Del Hoyo Gloria, González-Granado José María, Ramírez-Huesca Marta, Zorita Virginia, Rubinstein Eric, Boucheix Claude, Sánchez-Madrid Francisco
Servicio de Inmunología, Hospital de la Princesa, Instituto de Investigación Sanitaria La Princesa, Madrid, Spain
Vascular Pathophysiology Research Area, Centro Nacional de Investigaciones Cardiovasculares Carlos III (CNIC), Madrid, Spain.
Mol Cell Biol. 2017 Jul 14;37(15). doi: 10.1128/MCB.00202-17. Print 2017 Aug 1.
Antigen presentation by dendritic cells (DCs) stimulates naive CD4 T cells, triggering T cell activation and the adaptive arm of the immune response. Newly synthesized major histocompatibility complex class II (MHC-II) molecules accumulate at MHC-II-enriched endosomal compartments and are transported to the plasma membrane of DCs after binding to antigenic peptides to enable antigen presentation. In DCs, MHC-II molecules are included in tetraspanin-enriched microdomains (TEMs). However, the role of tetraspanin CD9 in these processes remains largely undefined. Here, we show that CD9 regulates the T cell-stimulatory capacity of granulocyte-macrophage colony-stimulating factor (GM-CSF)-dependent bone marrow-derived DCs (BMDCs), without affecting antigen presentation by fms-like tyrosine kinase 3 ligand (Flt3L)-dependent BMDCs. CD9 knockout (KO) GM-CSF-dependent BMDCs, which resemble monocyte-derived DCs (MoDCs), induce lower levels of T cell activation than wild-type DCs, and this effect is related to a reduction in MHC-II surface expression in CD9-deficient MoDCs. Importantly, MHC-II targeting to the plasma membrane is largely impaired in immature CD9 KO MoDCs, in which MHC-II remains arrested in acidic intracellular compartments enriched in LAMP-1 (lysosome-associated membrane protein 1), and MHC-II internalization is also blocked. Moreover, CD9 participates in MHC-II trafficking in mature MoDCs, regulating its endocytosis and recycling. Our results demonstrate that the tetraspanin CD9 specifically regulates antigenic presentation in MoDCs through the regulation of MHC-II intracellular trafficking.
树突状细胞（DCs）的抗原呈递刺激初始CD4 T细胞，触发T细胞活化和免疫反应的适应性分支。新合成的主要组织相容性复合体II类（MHC-II）分子在富含MHC-II的内体区室中积累，并在与抗原肽结合后转运至DCs的质膜以实现抗原呈递。在DCs中，MHC-II分子包含在富含四跨膜蛋白的微结构域（TEMs）中。然而，四跨膜蛋白CD9在这些过程中的作用仍 largely undefined。在这里，我们表明CD9调节粒细胞-巨噬细胞集落刺激因子（GM-CSF）依赖性骨髓来源的DCs（BMDCs）的T细胞刺激能力，而不影响fms样酪氨酸激酶3配体（Flt3L）依赖性BMDCs的抗原呈递。与单核细胞衍生的DCs（MoDCs）相似的CD9基因敲除（KO）GM-CSF依赖性BMDCs诱导的T细胞活化水平低于野生型DCs，这种效应与CD9缺陷型MoDCs中MHC-II表面表达的降低有关。重要的是，在未成熟的CD9 KO MoDCs中，MHC-II靶向质膜在很大程度上受损，其中MHC-II仍停滞在富含LAMP-1（溶酶体相关膜蛋白1）的酸性细胞内区室中，并且MHC-II的内化也被阻断。此外，CD9参与成熟MoDCs中MHC-II的转运，调节其胞吞作用和再循环。我们的结果表明，四跨膜蛋白CD9通过调节MHC-II的细胞内转运特异性地调节MoDCs中的抗原呈递。
