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Phagocytosis of opsonized Treponema pallidum subsp. pallidum proceeds slowly
J D Alder1, L Friess, M Tengowski
1Department of Medical Microbiology and Immunology, University of Wisconsin Medical School, Madison.
Abstract:
Macrophages were found to phagocytize Treponema pallidum subsp. pallidum attached to polycarbonate filters. This environment simulated the in vivo interaction of surface-adherent treponemes with macrophages. The phagocytosis of T. pallidum subsp. pallidum was found to proceed slowly. Heat-killed T. pallidum subsp. pallidum were susceptible to opsonization with 2% immune serum, whereas live treponemes were resistant to this concentration of antibody. High concentrations of immune serum were found to increase phagocytosis of the spirochetes. Live T. pallidum subsp. pallidum had bound limited quantities of immunoglobulin G in vivo, and only opsonization with 20% immune serum resulted in a detectable increase in surface-bound immunoglobulin in vitro. Kinetic studies suggested a steady rate of phagocytosis that is considerably slower than with other bacteria. Scanning electron microscopy studies of the phagocytizing macrophages showed that the treponemes were detached from the membrane filters and scooped onto the ruffled portion of the macrophage surface. This lengthy physical process, along with the lack of a dramatic increase in ingestion after opsonization, may account for the slow rate of phagocytosis.
Insights
Macrophages slowly phagocytize Treponema pallidum subsp. pallidum, a key step in syphilis infection. Opsonization with high immune serum concentrations enhances this process, but live bacteria remain resistant to low concentrations.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Macrophages play a crucial role in the immune response against bacterial pathogens.
- Treponema pallidum subsp. pallidum is the causative agent of syphilis.
- Understanding the interaction between macrophages and T. pallidum is vital for developing effective treatments.
Purpose of the Study:
- To investigate the phagocytosis of Treponema pallidum subsp. pallidum by macrophages.
- To determine the effect of opsonization on the phagocytosis rate.
- To elucidate the mechanisms underlying the interaction between macrophages and surface-adherent T. pallidum.
Main Methods:
- Simulated in vivo conditions using polycarbonate filters for surface-adherent treponemes.
- Opsonization experiments with varying concentrations of immune serum.
- Kinetic studies to measure phagocytosis rates.
- Scanning electron microscopy to visualize cellular interactions.
Main Results:
- Phagocytosis of T. pallidum subsp. pallidum by macrophages is a slow process.
- Live treponemes are resistant to low concentrations of immune serum but susceptible to high concentrations.
- High immune serum concentrations increase phagocytosis and surface-bound immunoglobulin G.
- Scanning electron microscopy revealed a lengthy physical process for treponeme engulfment.
Conclusions:
- The slow phagocytosis rate of T. pallidum subsp. pallidum may be attributed to the complex physical interaction and limited opsonization effectiveness.
- Further research into enhancing macrophage-mediated clearance of T. pallidum is warranted.