Opsonin-independent adherence and intracellular development of Legionella pneumophila within U-937 cells

Can J Microbiol. 1993 Jul;39(7):718-22. doi: 10.1139/m93-103.


Legionella pneumophila adhered to and multiplied intracellularly in the human histiocytic lymphoma U-937 cell line. The infectious process was evaluated by viable bacterial cell colony counts and documented by transmission and scanning electron microscopy. In the absence of opsonins, wash-resistant bacterial adherence to host cells occurred within 1 h and attachment of 1 or 2 organisms per U-937 host cell involved close surface interactions at the prokaryotic and eukaryotic membranes. Intracellular multiplication of bacteria was maximal by 24 h after inoculation of cell monolayers. Release of L. pneumophila from these cells appeared as a lytic process that resulted in an increase in the numbers of microorganisms in the extracellular fluids and a concomitant decline in the number of intracellular bacteria. The course of cellular infection was completed by 72 h. The cellular and ultrastructural events of L. pneumophila adherence and uptake by U-937 cells in the absence of antibody or complement have been defined. In addition, this work further establishes the U-937 cell as a suitable model for investigating Legionella--host cell interactions.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Bacterial Adhesion / physiology*
  • Colony Count, Microbial
  • Humans
  • Legionella pneumophila / growth & development*
  • Legionella pneumophila / ultrastructure*
  • Lymphoma, Large B-Cell, Diffuse / ultrastructure*
  • Opsonin Proteins / physiology*
  • Tumor Cells, Cultured


  • Opsonin Proteins