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Production of an early release, M(r) 36,000 monokine by stimulated rat macrophages
N M Hedberg1, N Hunter, C Soussou
1United Dental Hospital, Surry Hills, NSW, Australia.
Abstract:
Supernatants from rat peritoneal macrophage cultures stimulated with bacterial products contain a M(r) 36,000 factor that protects immature cortical thymocytes from loss of viability over a 4-hr incubation period in vitro. This effect could not be produced with purified transforming growth factor-beta or recombinant interleukin-6 (IL-6). Further, the partially purified M(r) 36,000 fraction was inactive in bioassays for IL-1 and tumour necrosis factor. Maximal production of the factor occurred 2 hr after the addition of 20 micrograms/ml of lipopolysaccharide, as assessed by the titre resulting in 100% protection of thymocytes in a viability assay. The detection of protective activity within 5 min after addition of the stimulant could be attributed to the release of intracellular stores but protein synthesis was required to account for the increasing titre up to peak levels. The titre fell rapidly after 2 hr so that activity could not be detected at 4 hr. This profile of release was refractory to repeated stimulation with lipopolysaccharide. Conjoint addition of lipopolysaccharide and indomethacin, did, however, allow release in response to subsequent challenge. Related to this finding, prostaglandin E2 completely inhibited the release of protective activity.
Insights
Rat macrophages release a 36,000 M(r) factor protecting thymocytes from death. This immune factor, distinct from known cytokines, is regulated by lipopolysaccharide and prostaglandin E2, offering insights into thymocyte survival mechanisms.
Area of Science:
- Immunology
- Cell Biology
Background:
- Immune cells like macrophages play a crucial role in regulating immune responses.
- Thymocytes, immature T cells, are vulnerable to cell death during their development.
- Understanding factors that promote thymocyte survival is vital for immune system health.
Purpose of the Study:
- To identify and characterize a novel protective factor released by macrophages.
- To investigate the kinetics and regulation of this protective factor's release.
- To determine the factor's role in protecting thymocytes from cell death in vitro.
Main Methods:
- Rat peritoneal macrophages were cultured and stimulated with bacterial products (lipopolysaccharide).
- Supernatants were analyzed for protective activity against thymocyte loss using viability assays.
- Partial purification of the active factor and bioassays for known cytokines were performed.
- Kinetics of factor release and the effects of indomethacin and prostaglandin E2 were studied.
Main Results:
- A M(r) 36,000 factor was identified in macrophage supernatants that protected thymocytes.
- This factor was distinct from transforming growth factor-beta, IL-6, IL-1, and tumor necrosis factor.
- Maximal factor production occurred at 2 hours post-lipopolysaccharide stimulation, requiring protein synthesis.
- Prostaglandin E2 inhibited the release of the protective factor, while indomethacin modulated its release profile.
Conclusions:
- Macrophages produce a novel M(r) 36,000 factor that enhances thymocyte viability.
- The release of this factor is regulated by lipopolysaccharide and prostaglandins.
- This finding contributes to understanding macrophage-mediated regulation of thymocyte development and survival.