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Macrophage-mediated killing of opsonized Treponema pallidum
S A Baker-Zander1, S A Lukehart
1Department of Medicine, University of Washington School of Medicine, Seattle.
Abstract:
The ability of proteose peptone-induced normal rabbit peritoneal macrophages to kill Treponema pallidum subspecies pallidum in vitro is demonstrated. Treponemes and 10% heated immune or normal sera were incubated with macrophages at a ratio of 1:200. After 2-10 h of incubation, these mixtures were injected intradermally at duplicate sites on normal rabbits. Maximal killing (failure to develop lesions) was seen at 10 h of incubation with immune serum: Only 7% (1/14) of lesions developed compared with 90% (9/10) after incubation in the presence of normal serum (P less than .001). Maximal phagocytosis (detected by immunofluorescence) occurred by 8 h in the presence of immune serum, when 90% of macrophages had ingested treponemes. At this point, however, 70% of lesion sites from macrophages incubated with treponemes and immune serum still developed, suggesting that effective killing may require at least 2 h after phagocytosis.
Insights
Normal rabbit macrophages effectively kill Treponema pallidum subspecies pallidum in vitro with immune serum. Killing requires at least 2 hours post-phagocytosis for optimal efficacy.
Area of Science:
- Immunology
- Microbiology
Background:
- Macrophages play a crucial role in host defense against bacterial pathogens.
- Treponema pallidum subspecies pallidum is the causative agent of syphilis.
Purpose of the Study:
- To investigate the in vitro killing capacity of normal rabbit peritoneal macrophages against Treponema pallidum subspecies pallidum.
- To determine the role of immune serum in macrophage-mediated treponemal killing.
Main Methods:
- Proteose peptone-induced rabbit peritoneal macrophages were incubated with Treponema pallidum subspecies pallidum and either heated immune or normal rabbit serum.
- Macrophage-treponeme mixtures were incubated for 2-10 hours and then injected intradermally into normal rabbits.
- Phagocytosis was assessed by immunofluorescence, and lesion development indicated treponemal survival.
Main Results:
- Maximal killing of Treponema pallidum subspecies pallidum was observed after 10 hours of incubation with immune serum, with only 7% lesion development compared to 90% with normal serum (P < .001).
- Maximal phagocytosis (90% of macrophages) occurred by 8 hours with immune serum.
- Despite high phagocytosis rates, 70% of lesion sites still developed, suggesting a 2-hour post-phagocytosis period is necessary for effective killing.
Conclusions:
- Normal rabbit peritoneal macrophages can kill Treponema pallidum subspecies pallidum in vitro, particularly when opsonized with immune serum.
- Effective killing of Treponema pallidum subspecies pallidum by macrophages requires a minimum of 2 hours after phagocytosis.
- These findings highlight the importance of immune serum and sufficient incubation time for macrophage-mediated clearance of T. pallidum.