title: Fate of Mycobacterium tuberculosis in peroxidase-loaded resting murine macrophages.
abstract: BACKGROUND
  Myeloperoxidase (MPO), in the presence of hydrogen peroxide and a halide represent an efficient microbicidal mechanism of phagocytic cells. MPO is abundant in neutrophils which also respond to infection by producing large amounts of reactive oxygen species (ROS). MPO, ROS and halide constitute a very toxic antimicrobial system (called the Klebanoff system or KS). Resting mature macrophages do not contain granular MPO and thus are unable to kill pathogenic mycobacteria and some other microorganisms by this system.
  
  
  METHODS
  Under the hypothesis that transforming macrophages into peroxidase-positive (PO(+)) cells, these cells would be able to kill Mycobacterium tuberculosis, in this study, mature macrophages were loaded with exogenous peroxidase and were tested for their capacity to kill the Mycobacterium in the presence or in the absence of hydrogen peroxide.
  
  
  RESULTS
  It was found that PO-loaded macrophages eagerly ingest M. tuberculosis, but do not show a significant mycobactericidal activity on this microorganism despite that it is highly susceptible to the Klebanoff system in vitro. Failure of PO-loaded macrophages to kill M. tuberculosis may obey either to an inappropriate location of the exogenous PO in these cells or more likely, to the presence of efficient detoxifying mechanisms in the bacteria. On the contrary, MPO-loaded or unloaded macrophages efficiently killed Listeria monocytogenes.
  
  
  CONCLUSIONS
  The lack of granular MPO in mature macrophages, and the predilection of mycobacteria to infect these cells are two situations that favor the development of tuberculosis and related diseases, such as leprosy and Buruli ulcer.
authors.affiliation: Departamento de Inmunología, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, México, D.F., México.
authors.forename: Melby Dessiré
authors.initials: MD
authors.lastname: Mendoza-Aguilar
authors.affiliation: Departamento de Inmunología, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, México, D.F., México.
authors.forename: Patricia
authors.initials: P
authors.lastname: Arce-Paredes
authors.affiliation: Departamento de Inmunología, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, México, D.F., México.
authors.forename: Mayda
authors.initials: M
authors.lastname: Aquino-Vega
authors.affiliation: Departamento de Inmunología, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, México, D.F., México.
authors.forename: Sandra
authors.initials: S
authors.lastname: Rodríguez-Martínez
authors.affiliation: Departamento de Inmunología, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, México, D.F., México. Electronic address: rojas_espinosa@hotmail.com.
authors.forename: Oscar
authors.initials: O
authors.lastname: Rojas-Espinosa
keywords: Macrophages; Mycobacterium tuberculosis; Peroxidase