title: Processing of Mycobacterium tuberculosis antigen 85B involves intraphagosomal formation of peptide-major histocompatibility complex II complexes and is inhibited by live bacilli that decrease phagosome maturation.
abstract: 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.
authors.affiliation: Institute of Pathology, Case Western Reserve University, 10900 Euclid Ave., Cleveland, OH 44106-4943 USA. lxr2@po.cwru.edu
authors.forename: L
authors.initials: L
authors.lastname: Ramachandra
authors.forename: E
authors.initials: E
authors.lastname: Noss
authors.forename: W H
authors.initials: WH
authors.lastname: Boom
authors.forename: C V
authors.initials: CV
authors.lastname: Harding
mesh_terms: D000217:Acyltransferases; D000818:Animals; D017951:Antigen Presentation; D000942:Antigens, Bacterial; D015703:Antigens, CD / Q000378:metabolism; D000944:Antigens, Differentiation, B-Lymphocyte / Q000032:analysis; D001426:Bacterial Proteins / Q000378:metabolism*; D015153:Blotting, Western; D002499:Centrifugation, Density Gradient; D000949:Histocompatibility Antigens Class II / Q000032:analysis* / Q000378:metabolism*; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009169:Mycobacterium tuberculosis / Q000276:immunology*; D010588:Phagosomes / Q000378:metabolism*
chemical_list: D000942:Antigens, Bacterial; D015703:Antigens, CD; D000944:Antigens, Differentiation, B-Lymphocyte; D001426:Bacterial Proteins; C416189:H2-M antigens; D000949:Histocompatibility Antigens Class II; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins; C045084:invariant chain; D000217:Acyltransferases; C121433:antigen 85B, Mycobacterium tuberculosis