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Ultrastructural localization of interleukin 1 in human peripheral blood monocytes; evidence for IL-1 beta in
J E Beesley1, R Bomford, J A Schmidt
1Department of Pharmacology, Wellcome Research Laboratories, Beckenham, Kent, UK.
Abstract:
The pathway of interleukin 1 (IL-1) secretion from the cell remains unclear. IL-1 beta is the major form produced by human monocytes, and is synthesized as a precursor of 35 kDa which is processed to the extracellular biologically active 17 kDa form. We have examined the intracellular localization of IL-1 beta in lipopolysaccharide (LPS)-stimulated human peripheral blood monocytes, by immunocytochemistry and immunoprecipitation of subcellular fractions. LPS treatment slightly damaged the cells. Unstimulated cells showed very little immunolabelling. In contrast, there was heavy immunolabelling on LPS stimulated cells. Immunolabelling occurred within the cytoplasm, nucleus and mitochondria. There was no immunolabelling on the membranous secretory organelles and the plasma membrane. Blebs of cytoplasm budding from the cell surface were immunolabeled, suggesting an alternative route of secretion of IL-1 beta from the cell. Immunoprecipitation studies confirmed these results.
Insights
The secretion pathway for interleukin 1 beta (IL-1 beta) from monocytes is unclear. Researchers found IL-1 beta in cytoplasm, nucleus, and mitochondria, suggesting a novel secretion route via cell blebs.
Area of Science:
- Immunology
- Cell Biology
Background:
- Interleukin 1 beta (IL-1 beta) is a key inflammatory cytokine produced by human monocytes.
- IL-1 beta is synthesized as a 35 kDa precursor and processed into a 17 kDa extracellular form.
- The precise mechanism of IL-1 beta cellular secretion remains largely unknown.
Purpose of the Study:
- To investigate the intracellular localization of IL-1 beta in lipopolysaccharide (LPS)-stimulated human peripheral blood monocytes.
- To elucidate the cellular pathway involved in IL-1 beta secretion.
Main Methods:
- Immunocytochemistry was used to detect IL-1 beta intracellularly.
- Immunoprecipitation of subcellular fractions analyzed IL-1 beta localization.
- Human peripheral blood monocytes were stimulated with lipopolysaccharide (LPS).
Main Results:
- LPS stimulation led to significant intracellular IL-1 beta immunolabeling in monocytes.
- IL-1 beta was localized within the cytoplasm, nucleus, and mitochondria.
- No IL-1 beta was detected on secretory organelles or the plasma membrane.
- Immunolabeled cytoplasmic blebs budding from the cell surface suggested an alternative secretion pathway.
Conclusions:
- IL-1 beta secretion from monocytes may not follow the classical secretory pathway.
- Cellular blebbing represents a potential novel mechanism for IL-1 beta release.
- Further research is needed to confirm this alternative secretion route.