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Attachment of virulent Treponema pallidum to human mononuclear phagocytes
Abstract:
The predominant phagocyte in established human syphilitic lesions is the mononuclear phagocyte. As these leucocytes may be important in immunity to Treponema pallidum, the initial interaction between human phagocytes and pathogenic T. pallidum (Nichols strain) was studied in vitro. Motile, virulent T. pallidum attach to the surface membrane of phagocytes but are not ingested by these cells. Heated, non-motile treponemes are not cell-associated but are observed free in the extracellular medium. Attachment is polar, at one or both terminal portions of the treponeme, and is neither serum- nor complement-dependent. Ingestion of virulent treponemes was not observed by phase-contrast or by electron microscopy in the presence of normal human or rabbit serum and complement. Techniques were chosen to preserve both the fragile surface constituents of the treponeme and the phagocytic function of mononuclear cells. Unfixed preparations were observed by phase-contrast microscopical examination during incubation to differentiate motile from non-motile organisms and fixed preparations were used for quantitation of attachment. This model should be useful for studying humoral and cell-mediated immunity in syphilis.
Insights
Human phagocytes interact with pathogenic Treponema pallidum by attaching to their surface but not ingesting them. This interaction is crucial for understanding immunity to syphilis.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Mononuclear phagocytes are the primary cells in human syphilitic lesions.
- These phagocytes may play a key role in immunity against Treponema pallidum.
Purpose of the Study:
- To investigate the initial in vitro interaction between human phagocytes and pathogenic Treponema pallidum (Nichols strain).
- To understand the early mechanisms of host-pathogen interaction in syphilis.
Main Methods:
- Utilized in vitro models with human phagocytes and virulent T. pallidum (Nichols strain).
- Employed phase-contrast and electron microscopy for observation.
- Used unfixed and fixed preparations to assess attachment and motility.
- Preserved fragile treponemal surface components and phagocytic cell function.
Main Results:
- Motile, virulent T. pallidum attach to the phagocyte surface membrane but are not ingested.
- Non-motile treponemes do not associate with cells.
- Attachment is polar and independent of serum or complement.
- No ingestion of virulent treponemes was observed with normal human or rabbit serum and complement.
Conclusions:
- Human phagocytes bind but do not internalize virulent T. pallidum.
- The attachment mechanism is specific and does not rely on opsonization.
- This in vitro model provides a platform for studying syphilis immunity.