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Activation of murine macrophages. I. Different pattern of activation by poly I:C than by lymphokine or LPS
Abstract:
The ability of poly I:C to activate mouse macrophages (M phi) to become tumoricidal was evaluated and compared with the ability of 2 other agents, lipopolysaccharide (LPS) and M phi-activating factor (MAF), to induce a tumoricidal state. All these agents were able to stimulate proteose-peptone-elicited M phi to kill RL male 1 tumor cells in an 18-hr 51Cr release cytotoxicity assay. High levels of cytotoxicity were obtained with concentrations as low as 1 microgram/ml of LPS or poly I:C and with 1/81 dilution of MAF. However, in the presence of reagents shown to contain less than 0.01 ng/ml of LPS by the LAL assay (LPS free), we found that poly I:C induced strong reactivity, whereas MAF was ineffective. The addition of 10 ng/ml of LPS during the stimulation period did not enhance the cytotoxicity induced by poly I:C, but it did restore MAF-induced, M phi-mediated cytotoxicity. In addition, poly I:C induced strong tumoricidal activity in resident M phi and in peritoneal exudate cells from the genetically defective C3H/HeJ mice that normally do not respond to LPS and MAF treatment. Therefore, it seems that although LPS is required as a second signal for MAF-induced cytotoxicity, such a second signal is not required for poly I:C-induced cytotoxicity. From the above results, it appears that poly I:C is a more powerful activating agent than LPS and MAF and either activates M phi via a different pathway or is effective on subpopulations of M phi that are not activated by the other agents.
Insights
Poly I:C effectively activates mouse macrophages (M phi) to kill tumor cells, even without lipopolysaccharide (LPS). Unlike MAF, poly I:C functions independently of LPS, suggesting a distinct activation pathway or targeting unique M phi subpopulations.
Area of Science:
- Immunology
- Cell Biology
- Cancer Research
Background:
- Macrophages (M phi) play a crucial role in tumor immunity.
- Activation of M phi can lead to tumoricidal activity.
- Lipopolysaccharide (LPS) and M phi-activating factor (MAF) are known M phi activators.
Purpose of the Study:
- To compare the efficacy of poly I:C, LPS, and MAF in activating mouse macrophages for tumor cell killing.
- To investigate the requirement of LPS as a second signal for MAF and poly I:C induced M phi cytotoxicity.
- To evaluate the activation of M phi from genetically LPS-unresponsive mice.
Main Methods:
- Proteose-peptone-elicited mouse macrophages were stimulated with poly I:C, LPS, or MAF.
- Tumoricidal activity was assessed using an 18-hr 51Cr release cytotoxicity assay against RL male 1 tumor cells.
- Experiments were conducted in LPS-free conditions and with C3H/HeJ mice (LPS non-responsive).
Main Results:
- Poly I:C, LPS, and MAF all induced M phi-mediated cytotoxicity.
- Poly I:C induced strong M phi reactivity even in LPS-free conditions and in C3H/HeJ mice.
- MAF-induced cytotoxicity was ineffective in LPS-free conditions and required LPS as a second signal, unlike poly I:C.
Conclusions:
- Poly I:C is a potent activator of mouse macrophages for tumoricidal activity.
- Poly I:C activates M phi independently of LPS, suggesting a distinct signaling pathway or targeting specific M phi subsets.
- Poly I:C represents a more powerful activating agent than LPS and MAF for inducing M phi-mediated tumor cell killing.