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Induction of activated macrophages in C3H/HeJ mice by avirulent Salmonella
R Schafer1, C A Nacy, T K Eisenstein
1Department of Microbiology and Immunology, Temple University School of Medicine, Philadelphia, PA 19140.
Abstract:
A single injection of viable Salmonella typhimurium SL3235, an avirulent organism blocked in the aromatic pathway, induced the generation of activated peritoneal macrophages in three different C3H mouse strains, including macrophage-defective C3H/HeJ mice. Macrophages obtained from immunized mice were cytotoxic for B16 melanoma cells, P815 mastocytoma cells, and TU-5 fibrosarcoma cells and microbicidal in vitro for the obligate, intracellular, protozoan parasite Leishmania major. The capacity of live SL3235 to activate C3H/HeJ macrophages contrasts with the failure of live Bacillus Calmette-Guérin to induce activated macrophages in this mouse strain. Although viable SL3235 were capable of fully activating cells of both normal and defective mice, a dose-dependent difference was observed in the number of organisms necessary for induction of tumoricidal macrophages in C3HeB/FeJ (normal) and C3H/HeJ (defective) animals. As few as 80 viable SL3235 were capable of activating C3HeB/FeJ macrophages whereas 5 X 10(4) organisms were required to activate C3H/HeJ macrophages. Maximal macrophage activation occurred 7 to 10 days after SL3235 inoculation in C3H/HeJ and C3HeB/FeJ mice. Acetone-killed cells of SL3235 had some but not all of the activity of the living Salmonella. A single in vivo injection of the nonviable preparation resulted in the induction of tumoricidal macrophages in C3HeB/FeJ but not in C3H/HeJ mice, even when tested over a wide dosage range. Injection of acetone-killed cells of SL3235 did, however, result in a population of primed macrophages in C3H/HeJ mice, as explanted cells could be induced to express activated macrophage effector activities after additional treatment in vitro with either LPS or IFN-gamma. Thus, in vivo administration of viable SL3235 is, by itself, capable of eliciting the full series of steps required for activation of C3H/HeJ macrophages, whereas killed SL3235 only provides signals sufficient to prime these defective macrophages for further activation in vitro. AI 15613
Insights
Viable Salmonella typhimurium SL3235 activates macrophages in normal and defective mice, demonstrating potent anti-tumor and anti-parasitic activity. Killed SL3235 primes macrophages in defective mice for further activation.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Macrophages play a crucial role in innate and adaptive immunity.
- Defective macrophage activation can impair host defense against pathogens and tumors.
- Salmonella typhimurium SL3235 is an avirulent strain useful for studying macrophage activation.
Purpose of the Study:
- To investigate the ability of viable and nonviable Salmonella typhimurium SL3235 to induce activated peritoneal macrophages in different C3H mouse strains.
- To compare the efficacy of SL3235 with Bacillus Calmette-Guérin in activating macrophages.
- To determine the dose-dependency and kinetics of macrophage activation by SL3235.
Main Methods:
- Administration of viable and acetone-killed Salmonella typhimurium SL3235 to C3H/HeJ (macrophage-defective) and C3HeB/FeJ (normal) mice.
- Assay of macrophage cytotoxic activity against tumor cell lines (B16 melanoma, P815 mastocytoma, TU-5 fibrosarcoma).
- Assessment of macrophage microbicidal activity against Leishmania major.
- In vitro activation of primed macrophages with LPS or IFN-gamma.
Main Results:
- Viable SL3235 induced cytotoxic and microbicidal activated macrophages in both normal and defective C3H mice.
- A lower dose of viable SL3235 was required for activation in normal mice compared to defective mice.
- Maximal macrophage activation occurred 7-10 days post-inoculation.
- Acetone-killed SL3235 induced tumoricidal macrophages in normal mice but only primed macrophages in defective mice.
Conclusions:
- Viable Salmonella typhimurium SL3235 is a potent inducer of fully activated macrophages, effective even in macrophage-defective mice.
- The dose of viable SL3235 required for macrophage activation is dose-dependent and differs between normal and defective mice.
- Nonviable SL3235 can prime macrophages, suggesting that live bacteria are necessary for complete in vivo activation in defective strains.