The Journal of Experimental Medicine
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Published 12 November 2001. doi:10.1084/jem.194.10.1421
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© Rockefeller University Press, 0022-1007/2001/11/1421/ $5.00
The Journal of Experimental Medicine, Volume 194, Number 10, November 19, 2001 1421-1432

Original Article

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

Lakshmi Ramachandra1, Erika Noss1,2, W. Henry Boom2 and Clifford V. Harding1

1 Institute of Pathology, Case Western Reserve University, Cleveland, OH 44106
2 Division of Infectious Diseases, Case Western Reserve University, Cleveland, OH 44106

Address correspondence to Lakshmi Ramachandra, Department of Pathology, BRB 947, Case Western Reserve University, 10900 Euclid Ave., Cleveland, OH 44106-4943. Phone: 216-368-1287; Fax: 216-368-1300; E-mail: lxr2{at}po.cwru.edu

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-Ab 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-Ab 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.

Key Words: Mycobacterium tuberculosis • phagosome • MHC • antigen processing • antigen presentation


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