Ramachandra L, Noss E, Boom W H, Harding C V
Institute of Pathology, Case Western Reserve University, 10900 Euclid Ave., Cleveland, OH 44106-4943 USA.
J Exp Med. 2001 Nov 19;194(10):1421-32. doi: 10.1084/jem.194.10.1421.
Mycobacterium tuberculosis (MTB) inhibits phagosomal maturation to promote its survival inside macrophages. Control of MTB infection requires CD4 T cell responses and major histocompatibility complex (MHC) class II (MHC-II) processing of MTB antigens (Ags). To investigate phagosomal processing of MTB Ags, phagosomes containing heat-killed (HK) or live MTB were purified from interferon-gamma (IFN-gamma)-activated macrophages by differential centrifugation and Percoll density gradient subcellular fractionation. Flow organellometry and Western blot analysis showed that MTB phagosomes acquired lysosome-associated membrane protein-1 (LAMP-1), MHC-II, and H2-DM. T hybridoma cells were used to detect MTB Ag 85B(241-256)-I-A(b) complexes in isolated phagosomes and other subcellular fractions. These complexes appeared initially (within 20 min) in phagosomes and subsequently (>20 min) on the plasma membrane, but never within late endocytic compartments. Macrophages processed HK MTB more rapidly and efficiently than live MTB; phagosomes containing live MTB expressed fewer Ag 85B(241-256)-I-A(b) complexes than phagosomes containing HK MTB. This is the first study of bacterial Ag processing to directly show that peptide-MHC-II complexes are formed within phagosomes and not after export of bacterial Ags from phagosomes to endocytic Ag processing compartments. Live MTB can alter phagosome maturation and decrease MHC-II Ag processing, providing a mechanism for MTB to evade immune surveillance and enhance its survival within the host.
结核分枝杆菌（MTB）抑制吞噬体成熟以促进其在巨噬细胞内的存活。控制MTB感染需要CD4 T细胞反应以及MTB抗原（Ags）的主要组织相容性复合体（MHC）II类（MHC-II）加工。为了研究MTB Ags的吞噬体加工过程，通过差速离心和Percoll密度梯度亚细胞分级分离，从干扰素-γ（IFN-γ）激活的巨噬细胞中纯化出含有热灭活（HK）或活MTB的吞噬体。流式细胞器分析和蛋白质印迹分析表明，MTB吞噬体获得了溶酶体相关膜蛋白-1（LAMP-1）、MHC-II和H2-DM。T杂交瘤细胞用于检测分离的吞噬体和其他亚细胞组分中的MTB Ag 85B(241-256)-I-A(b)复合物。这些复合物最初（20分钟内）出现在吞噬体中，随后（>20分钟）出现在质膜上，但从未出现在晚期内吞区室中。巨噬细胞处理HK MTB比活MTB更快、更有效；含有活MTB的吞噬体比含有HK MTB的吞噬体表达的Ag 85B(241-256)-I-A(b)复合物更少。这是第一项关于细菌Ag加工的研究，直接表明肽-MHC-II复合物在吞噬体内形成，而不是在细菌Ags从吞噬体输出到内吞Ag加工区室后形成。活MTB可以改变吞噬体成熟并减少MHC-II Ag加工，为MTB逃避免疫监视并增强其在宿主体内的存活提供了一种机制。
