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Processing of Mycobacterium tuberculosis antigen 85B involves intraphagosomal formation of peptide-major

L Ramachandra1, E Noss, W H Boom

  • 1Institute of Pathology, Case Western Reserve University, 10900 Euclid Ave., Cleveland, OH 44106-4943 USA. lxr2@po.cwru.edu

The Journal of Experimental Medicine
|November 21, 2001
PubMed
Summary

Mycobacterium tuberculosis (MTB) evades immune surveillance by inhibiting phagosomal maturation. This study reveals that peptide-MHC-II complexes form within phagosomes, but live MTB impairs this crucial antigen processing pathway.

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Area of Science:

  • Immunology
  • Cell Biology
  • Microbiology

Background:

  • Mycobacterium tuberculosis (MTB) survives within macrophages by disrupting phagosomal maturation.
  • Effective control of MTB infection relies on CD4 T cell responses and major histocompatibility complex (MHC) class II antigen processing.
  • Investigating antigen processing within phagosomes is key to understanding MTB immune evasion.

Purpose of the Study:

  • To investigate the phagosomal processing of MTB antigens (Ags) and the formation of peptide-MHC-II complexes.
  • To determine if antigen processing occurs within phagosomes or after antigen export.

Main Methods:

  • Purification of MTB-containing phagosomes from IFN-gamma-activated macrophages.
  • Flow organellometry and Western blot analysis to detect LAMP-1, MHC-II, and H2-DM.
  • T hybridoma cells used to detect specific MTB Ag 85B-I-A(b) complexes.

Main Results:

  • MTB phagosomes acquired LAMP-1, MHC-II, and H2-DM.
  • Peptide-MHC-II complexes formed within phagosomes within 20 minutes and later appeared on the plasma membrane.
  • Heat-killed MTB were processed more efficiently than live MTB, with fewer complexes on live MTB phagosomes.

Conclusions:

  • This study provides the first direct evidence of peptide-MHC-II complex formation within phagosomes.
  • Live MTB hinders phagosome maturation and MHC-II antigen processing, facilitating immune evasion and survival.
  • Understanding this mechanism is crucial for developing strategies against MTB infection.