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Immuno-inductive and immuno-suppressive influence of human mononuclear phagocytes cultured in vitro
Abstract:
DNA-synthesis, as measured by 3H thymidine incorporation, in immune lymphocytes from human blood stimulated in vitro with PPD was shown to require monocytes. No such requirement was demonstrated for PHA-induced DNA-synthesis under the same conditions. Initial packing of cells by centrifugation was beneficial for the cultures stimulated by antigen, but not for the cultures stimulated by lectin, thus indicating the necessity for contact between monocytes and lymphocytes for antigen stimulation. Monocytes and macrophages preincubated with PPD indced DNA-synthesis in lymphocytes. Monocytes were found to be least as capable of retaining and presenting antigen as macrophages, and autologous macrophages presented antigen more efficiently than allogeneic macrophages. DNA-synthesis in lymphocytes, induced by adding PPD or PHA to the culture medium, was inhibited by a large number of monocytes. Macrophages caused inhibition under the same conditions, even a small number. DNA-synthesis in lymphocytes induced by PPD-preincubated monocytes and macrophages increased with increasing ratio of mononuclear phagocytes to lymphocytes up to a certain value. A further increase in the ratio caused inhibition, thus indicating both an immunoinductive and an immuno-suppressive influence of mononuclear phagocytes.
Insights
Monocytes are essential for antigen-specific lymphocyte DNA synthesis (3H thymidine incorporation) but not for PHA-induced synthesis. Mononuclear phagocytes have dual roles, acting as both immuno-inducers and suppressors.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Immune responses involve complex cell interactions.
- Mononuclear phagocytes, including monocytes and macrophages, play critical roles in immune regulation.
- Understanding the specific functions of these cells in lymphocyte activation is crucial.
Purpose of the Study:
- To investigate the role of monocytes in DNA synthesis of human lymphocytes stimulated by purified protein derivative (PPD) and phytohemagglutinin (PHA).
- To compare the antigen-presenting capabilities of monocytes and macrophages.
- To elucidate the dual immuno-inductive and immuno-suppressive effects of mononuclear phagocytes on lymphocyte proliferation.
Main Methods:
- Human blood lymphocytes were cultured in vitro and stimulated with PPD or PHA.
- 3H thymidine incorporation was used to measure DNA synthesis.
- Cellular interactions were studied by varying cell ratios and pre-incubation conditions.
- Autologous and allogeneic antigen presentation were assessed.
Main Results:
- Monocytes were required for PPD-induced lymphocyte DNA synthesis but not for PHA-induced synthesis.
- Cell packing enhanced antigen stimulation, indicating a need for monocyte-lymphocyte contact.
- Monocytes and macrophages pre-incubated with PPD induced lymphocyte DNA synthesis.
- Autologous macrophages were more efficient than allogeneic macrophages in antigen presentation.
- High numbers of monocytes and macrophages inhibited DNA synthesis, demonstrating a dose-dependent effect.
Conclusions:
- Monocytes are critical for antigen-specific lymphocyte activation.
- Mononuclear phagocytes exhibit both stimulatory and inhibitory functions in immune responses.
- The ratio of mononuclear phagocytes to lymphocytes is a key factor in modulating immune cell proliferation.