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Dissociation of bactericidal activity from other functions of activated macrophages in exudates induced by
Abstract:
Macrophages displayed increased spreading, increased Fc-receptor-mediated phagocytosis, and increased secretion of plasminogen activator when collected from the peritoneal cavities of either Listeria-immune mice challenged intraperitoneally 3 days earlier with Listeria or nonimmune mice injected intraperitoneally 3 days earlier with fluid thioglycolate medium. In contrast, macrophages from the thioglycolate-induced peritoneal exudates were severely impaired in vitro in their ability to destroy Listeria. Injection of thioglycolate markedly interfered with the destruction of sublethal intraperitoneal challenge of Listeria, which resulted in nonimmune animals dying of an overwhelming systemic infection. In animals immune to Listeria, injection of thioglycolate delayed the onset of the expression of immunity to an intraperitoneal challenge of bacteria. The thioglycolate-induced suppression of bactericidal activity was determined to be confined to the site of injection. Results of experiments indicated that the colloidal agar in thioglycolate medium was the cause of the impairment of macrophage bactericidal activity. In addition to the impairment of bactericidal activity induced by agar, additional studies showed that an intraperitoneal injection of colloidal agar (0.075% wt/vol) by itself was a sufficient inflammatory stimulus for the accumulation of a large number of host phagocytic cells.
Insights
Thioglycolate medium impairs macrophage bactericidal activity, hindering Listeria destruction in mice. Colloidal agar within the medium is identified as the primary cause of this immune suppression.
Area of Science:
- Immunology
- Microbiology
Background:
- Macrophages are key immune cells involved in phagocytosis and pathogen destruction.
- Thioglycolate medium is commonly used to elicit peritoneal macrophages for experimental study.
Purpose of the Study:
- To investigate the effect of thioglycolate medium injection on macrophage function and host defense against Listeria infection.
- To identify the component within thioglycolate medium responsible for any observed immune impairment.
Main Methods:
- Macrophages were collected from mice injected with thioglycolate medium or from Listeria-immune mice.
- Macrophage functions including spreading, phagocytosis, and bactericidal activity were assessed in vitro.
- Mice were challenged with Listeria following thioglycolate injection to evaluate in vivo host defense.
Main Results:
- Macrophages from thioglycolate-injected mice showed increased spreading and phagocytosis but impaired ability to destroy Listeria.
- Thioglycolate injection compromised host defense against Listeria, leading to increased mortality in non-immune mice and delayed immunity in immune mice.
- Colloidal agar present in thioglycolate medium was identified as the causative agent for the suppression of macrophage bactericidal activity.
Conclusions:
- Thioglycolate medium, specifically its colloidal agar component, impairs macrophage bactericidal function.
- This impairment can compromise host defense against bacterial infections like Listeria.
- Colloidal agar itself acts as an inflammatory stimulus, recruiting phagocytic cells.