title: Macropinocytosis is responsible for the uptake of pathogenic and non-pathogenic mycobacteria by B lymphocytes (Raji cells).
abstract: BACKGROUND
  The classical roles of B cells include the production of antibodies and cytokines and the generation of immunological memory, these being key factors in the adaptive immune response. However, their role in innate immunity is currently being recognised. Traditionally, B cells have been considered non-phagocytic cells; therefore, the uptake of bacteria by B cells is not extensively documented. In this study, we analysed some of the features of non-specific bacterial uptake by B lymphocytes from the Raji cell line. In our model, B cells were infected with Mycobacterium tuberculosis (MTB), Mycobacterium smegmatis (MSM), and Salmonella typhimurium (ST).
  
  
  RESULTS
  Our observations revealed that the Raji B cells were readily infected by the three bacteria that were studied. All of the infections induced changes in the cellular membrane during bacterial internalisation. M. smegmatis and S. typhimurium were able to induce important membrane changes that were characterised by abundant filopodia and lamellipodia formation. These membrane changes were driven by actin cytoskeletal rearrangements. The intracellular growth of these bacteria was also controlled by B cells. M. tuberculosis infection also induced actin rearrangement-driven membrane changes; however, the B cells were not able to control this infection. The phorbol 12-myristate 13-acetate (PMA) treatment of B cells induced filopodia and lamellipodia formation, the production of spacious vacuoles (macropinosomes), and the fluid-phase uptake that is characteristic of macropinocytosis. S. typhimurium infection induced the highest fluid-phase uptake, although both mycobacteria also induced fluid uptake. A macropinocytosis inhibitor such as amiloride was used and abolished the bacterial uptake and the fluid-phase uptake that is triggered during the bacterial infection.
  
  
  CONCLUSIONS
  Raji B cells can internalise S. typhimurium and mycobacteria through an active process, such as macropinocytosis, although the resolution of the infection depends on factors that are inherent in the virulence of each pathogen.
authors.affiliation: Immunology Department, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, México, D,F, México.
authors.forename: Blanca Estela
authors.initials: BE
authors.lastname: García-Pérez
authors.forename: Juan José
authors.initials: JJ
authors.lastname: De la Cruz-López
authors.forename: Jorge Ismael
authors.initials: JI
authors.lastname: Castañeda-Sánchez
authors.forename: Ana Rosa
authors.initials: AR
authors.lastname: Muñóz-Duarte
authors.forename: Alma Delia
authors.initials: AD
authors.lastname: Hernández-Pérez
authors.forename: Hilda
authors.initials: H
authors.lastname: Villegas-Castrejón
authors.forename: Ethel
authors.initials: E
authors.lastname: García-Latorre
authors.forename: Angel
authors.initials: A
authors.lastname: Caamal-Ley
authors.forename: Julieta
authors.initials: J
authors.lastname: Luna-Herrera
mesh_terms: D000199:Actins / Q000378:metabolism; D001402:B-Lymphocytes / Q000276:immunology* / Q000382:microbiology* / Q000502:physiology; D002460:Cell Line; D022081:Cell Surface Extensions; D006801:Humans; D020102:Mycobacterium smegmatis / Q000276:immunology*; D009169:Mycobacterium tuberculosis / Q000276:immunology*; D010873:Pinocytosis; D012486:Salmonella typhimurium / Q000276:immunology*; D014617:Vacuoles / Q000378:metabolism
chemical_list: D000199:Actins