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Extracellular cytolysis by activated macrophages: studies with macrophages on permeable membranes
Abstract:
Mouse peritoneal macrophages were allowed to adhere to discs cut from permeable membranes, then activated by incubation in lymphokine-rich supernates from ConA-stimulated spleen cells. Such filter-borne cultures of activated macrophages (AM) were cytotoxic for various target cells (Tc). The kinetics of the cytotoxic process could be monitored by removal of the filter-bound AM after increasing times of contact with Tc. Using 3 assay procedures to assess macrophage cytotoxicity, i.e. chromium-51 release, thymidine incorporation, and cloning inhibition, most of the damage to Tc was found to occur within 30 min to 2 h of interaction between the two cell types. The kinetics of the cytolytic effect were similar, whether Tc were in direct contact with AM or separated by the filter; thus cytotoxicity appeared to be mediated by a highly diffusible compound. Supernates of AM incubated with Tc for 1 to 4 h, but not of AM incubated alone, were toxic for Tc, suggesting that Tc provide a signal to AM, in the absence of which toxic intermediates fail to be released. Addition of catalase or peroxidase considerably reduced Tc destruction by AM, indicating that oxygen metabolites might play a role as mediators of AM cytotoxicity in the present experimental model.
Insights
Activated macrophages (AM) exhibit cytotoxicity against target cells (Tc) through a diffusible compound, with damage occurring rapidly. This process may involve oxygen metabolites and requires a signal from target cells for toxic intermediate release.
Area of Science:
- Immunology
- Cell Biology
Background:
- Macrophages play a crucial role in the immune response.
- Activated macrophages (AM) possess cytotoxic capabilities against various target cells (Tc).
Purpose of the Study:
- To investigate the kinetics and mechanisms of macrophage-mediated cytotoxicity.
- To identify potential mediators involved in the cytotoxic process.
Main Methods:
- Mouse peritoneal macrophages were cultured on permeable membranes and activated.
- Cytotoxicity was assessed using chromium-51 release, thymidine incorporation, and cloning inhibition assays.
- The role of diffusible compounds and oxygen metabolites was examined.
Main Results:
- Macrophage-induced damage to target cells occurred rapidly, primarily within 30 minutes to 2 hours of interaction.
- Cytotoxicity was mediated by a highly diffusible compound, effective even when cells were separated by a filter.
- Target cells appeared to provide a necessary signal for the release of toxic intermediates from activated macrophages.
- Catalase and peroxidase reduced target cell destruction, suggesting a role for oxygen metabolites.
Conclusions:
- Activated macrophages exert rapid, contact-independent cytotoxicity mediated by diffusible factors.
- Target cell recognition or signaling is crucial for the activation of cytotoxic mechanisms in macrophages.
- Oxygen metabolites are likely involved as mediators in this model of macrophage cytotoxicity.