Interferon-γ Induced Resistance to Legionella pneumophila in Susceptible A/J Mouse Macrophages

Abstract

Legionella pneumophila (Lp) grow in cultures in human, guinea pig, and mouse macrophages from A/J strain mice. Because exudate macrophages from this strain of mice have been reported deficient in responsiveness to lymphokines, we thought it of interest to document the extent of responsiveness to interferon-gamma in the context of growth restriction of Lp. Peritoneal exudate macrophages were obtained from A/J mice and cultured in either the presence or absence of recombinant interferon-gamma. These cultures were then infected with Lp and the extent of bacterial growth estimated 48 hr later by means of a colony-forming unit (CFU) assay and electron microscopy. Interferon-gamma treatment significantly restricted the number of CFUs in the culture at concentrations as low as 20 U/ml, but did not affect the uptake of bacteria by macrophages. Furthermore, treatment with interferon induced morphological changes consistent with activated macrophages. The involvement of oxygen-dependent mechanisms in phagocyte killing and growth restriction was examined by the use of inhibitors such as superoxide dismutase (SOD) and catalase. Neither one of these inhibitors of toxic oxygen metabolites affected the interferon-gamma-induced suppression of Lp growth. These results suggest that although thioglycolate-induced exudate macrophages from A/J mice support the growth of Lp, these cells readily respond to the activating influence of interferon-gamma. Furthermore, lymphokine treatment does not inhibit Lp uptake by macrophages and apparently restricts the growth of bacteria by mechanisms independent of the activity of toxic oxygen metabolites.

Transient Transgenic Expression of Gamma Interferon PromotesLegionella pneumophilaClearance in Immunocompetent Hosts

“…Rather, the IFN-␥ transgene is likely exerting important activating effects on the resident leukocytes in the lungs. This argument is supported by previously published findings that recombinant IFN-␥ activates alveolar macrophages and other monocytes to limit the growth of intracellular Legionella organisms in vitro (3,15,33,37,43). Likewise, our observations indicated that macrophages isolated from AdmIFN-␥-treated mice inhibited the growth of Legionella.…”

Activated Macrophages Infected with Legionella Inhibit T Cells by Means of MyD88-Dependent Production of Prostaglandins

“…Our observation that Legionella replication is restricted in IFN-␥-treated M is consistent with previous reports (23)(24)(25)51). Previous studies using M from A/J mice indicate that activated M restrict the growth of Legionella by a process that does not require production of reactive oxygen and nitrogen species and that is in part mediated by the sequestration of iron (51).…”

“…Ex vivo treatment of murine M and human monocytes with IFN-␥ restricts the intracellular growth of Legionella (23)(24)(25). Studies using electron microscopy have suggested that Legionella are able to create an ER-like organelle within IFN-␥-activated M, but the bacteria are unable to replicate within this compartment (23).…”

Interferon‐Gamma Reverses the Evasion of Birc1e/Naip5 Gene Mediated Murine Macrophage Immunity by Legionella pneumophila Mutant Lacking Flagellin

“…In previous studies, IFN-γ was shown to restrict L. pneumophila replication within A/J macrophages (9,19). Therefore, the effect of IFN-γ on the growth of the flaA mutant within C57BL/6 macrophages was of interest.…”