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Differential growth of Legionella pneumophila in guinea pig versus mouse macrophage cultures
Abstract:
Legionella pneumophila is a facultative intracellular bacterium which replicated well in inbred guinea pig strain 2 peritoneal macrophages at a low infectivity ratio. In contrast, the growth of this organism was markedly restricted in mouse (BDF1) peritoneal macrophages, even at a relatively high infectivity ratio. The initial uptake of L. pneumophila organisms by macrophages was similar in both animal species, and both groups of macrophages supported the growth of Listeria monocytogenes. Treatment of L. pneumophila with immune guinea pig serum did not result in restriction of bacterial growth in macrophages, but guinea pig macrophages were readily induced to suppress the growth of L. pneumophila by preincubation with supernatants obtained from mitogen-activated normal guinea pig splenocyte cultures. Thus, lymphokines generated from mitogen-stimulated guinea pig lymphocytes induced a restriction of growth of these organisms similar to that observed naturally with macrophages from mice, which are considered highly resistant to these bacteria. Although guinea pigs are considered highly susceptible to L. pneumophila infections and mice are considered relatively resistant, the mechanism of this difference is not clear. The results of the present study suggest that the restriction of L. pneumophila growth by macrophages relates to host susceptibility to infection and that cell populations permissive for L. pneumophila can be transformed to nonpermissive by products from stimulated lymphocytes but not by opsonization with immune serum.
Insights
Guinea pig macrophages normally support Legionella pneumophila growth, unlike mouse macrophages. Lymphokines from stimulated guinea pig lymphocytes can induce macrophages to restrict L. pneumophila, revealing a key mechanism in host resistance.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Legionella pneumophila (L. pneumophila) is an intracellular bacterium with varying susceptibility across host species.
- Guinea pigs are generally susceptible to L. pneumophila infections, while mice are considered resistant.
- The underlying mechanisms for differential host susceptibility remain unclear.
Purpose of the Study:
- To investigate the differential growth restriction of L. pneumophila in macrophages from guinea pigs and mice.
- To explore the role of lymphokines and immune serum in modulating macrophage permissiveness to L. pneumophila.
Main Methods:
- Comparative analysis of L. pneumophila replication in peritoneal macrophages from guinea pigs (strain 2) and mice (BDF1).
- Assessment of macrophage uptake of L. pneumophila and growth of Listeria monocytogenes as controls.
- Evaluation of the effect of immune guinea pig serum and supernatants from activated guinea pig splenocytes on L. pneumophila growth in macrophages.
Main Results:
- L. pneumophila replicated well in guinea pig macrophages but was restricted in mouse macrophages, irrespective of infectivity ratio.
- Macrophage uptake of L. pneumophila was similar in both species.
- Preincubation of guinea pig macrophages with lymphokine-containing supernatants induced L. pneumophila growth restriction, mimicking mouse macrophage resistance. Immune serum did not confer this restriction.
Conclusions:
- Macrophage permissiveness to L. pneumophila is linked to host susceptibility.
- Lymphokines derived from stimulated lymphocytes can transform permissive macrophages into non-permissive ones.
- Opsonization with immune serum does not induce growth restriction, highlighting the critical role of cell-mediated immune factors.