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The interaction between Treponema pallidum and human polymorphonuclear leukocytes
Abstract:
The interaction between polymorphonuclear leukocytes (PMNLs) and Treponema pallidum was studied. Intradermal injection of greater than or equal to 10(6) T. pallidum into rabbits caused a rapid accumulation of PMNLs. Human serum released chemotaxigenic factor (C5a) during incubation in vitro with T. pallidum. Incubation of T. pallidum with human PMNLs in vitro (ratio, 100:1) stimulated chemiluminescence. These responses were dependent upon the presence of both antibody and complement and were greatest when serum from a patient with late secondary syphilis was used as a chemotaxigenic source or for opsonization. Electron microscopic studies documented the rapid uptake of T. pallidum into membrane-bound vacuoles in the human PMNLs in vitro after incubation for as little as 5 min, with leukocyte degranulation and loss of treponemal integrity observed after 4 hr. T. pallidum were found within PMNLs 3 hr after intradermal inoculation of rabbits. These data show that PMNLs are attracted to, and appear to ingest, T. pallidum, but they fail to explain why inoculation of these organisms is not followed by eradication.
Insights
Polymorphonuclear leukocytes (PMNLs) are attracted to and ingest Treponema pallidum, a bacterium causing syphilis. However, this interaction doesn't lead to the eradication of the bacteria, leaving the mechanism unclear.
Area of Science:
- Immunology
- Microbiology
- Infectious Diseases
Background:
- Polymorphonuclear leukocytes (PMNLs) are key immune cells involved in early host defense against bacterial infections.
- Treponema pallidum is the causative agent of syphilis, a complex sexually transmitted infection.
- Understanding the initial host-pathogen interactions is crucial for developing effective treatment strategies.
Purpose of the Study:
- To investigate the interaction between human polymorphonuclear leukocytes (PMNLs) and Treponema pallidum in vitro and in vivo.
- To elucidate the role of complement and antibodies in PMNL-mediated responses to T. pallidum.
- To determine the fate of T. pallidum following phagocytosis by PMNLs.
Main Methods:
- Intradermal inoculation of rabbits with T. pallidum to study PMNL accumulation.
- In vitro incubation of T. pallidum with human serum to assess C5a release.
- Chemiluminescence assays to measure PMNL activation in response to T. pallidum.
- Electron microscopy to visualize the ultrastructural interactions between PMNLs and T. pallidum.
- In vivo studies in rabbits to track PMNLs and T. pallidum.
Main Results:
- Intradermal injection of T. pallidum induced rapid PMNL accumulation in rabbits.
- Human serum incubated with T. pallidum released chemotaxigenic factor (C5a).
- PMNLs showed stimulated chemiluminescence upon incubation with T. pallidum, requiring antibody and complement.
- Electron microscopy revealed rapid T. pallidum uptake by PMNLs, with subsequent degranulation and loss of treponemal integrity.
- T. pallidum was observed within rabbit PMNLs three hours post-inoculation.
Conclusions:
- PMNLs are recruited to T. pallidum and capable of phagocytosing the bacteria.
- Antibodies and complement significantly enhance PMNL responses to T. pallidum.
- Despite PMNLs' ability to ingest and damage T. pallidum, complete eradication does not occur, suggesting immune evasion mechanisms by the pathogen.