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Origin of circulating acute phase cytokines: modified proteins may trigger IL-6 production by macrophages.
1Institute of Molecular Biology, Jagiellonian University, Cracow, Poland.
Abstract:
Human peripheral blood monocytes isolated by centrifugation with Mono-Poly resolving medium, and human alveolar macrophages obtained by lung lavage during fiberoscopic bronchoscopy, were cultured in RPMI containing 2% foetal calf serum. The cultures were exposed to modified human proteins: alpha-1-antitrypsin cleaved with papain, fibrinogen degradation products (fraction D) purified from plasmin digest, and non-enzymatically glycosylated (glycated) serum albumin. Conditioned macrophage media were tested for the contents of acute phase cytokines by bioassay with hepatoma cells, and the concentration of interleukin-6 was determined with ELISA. Modified proteins stimulated macrophages to produce acute phase cytokines and the response was not abrogated by polymyxin B in distinction to stimulation of macrophages by endotoxin. Our data indicate that some proteolytically damaged proteins or the end glycosylation products formed in pathological states (acute inflammation, diabetes) may be responsible for the appearance of cytokines in the circulation.
Insights
Modified proteins like damaged alpha-1-antitrypsin and glycated albumin stimulate macrophages to produce cytokines. This suggests pathological protein modifications may cause circulating cytokines in inflammation and diabetes.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Macrophages play a crucial role in immune responses, including the production of cytokines.
- Pathological conditions such as inflammation and diabetes involve protein modifications.
- The role of modified proteins in stimulating cytokine production by macrophages requires further investigation.
Purpose of the Study:
- To investigate whether modified human proteins can stimulate macrophages to produce acute phase cytokines.
- To compare the stimulatory effects of proteolytically damaged proteins and non-enzymatically glycosylated proteins on macrophages.
- To explore the potential role of these modified proteins in the generation of circulating cytokines during pathological states.
Main Methods:
- Human peripheral blood monocytes and alveolar macrophages were isolated and cultured.
- Macrophage cultures were exposed to modified human proteins: papain-cleaved alpha-1-antitrypsin, fibrinogen degradation products (fraction D), and glycated serum albumin.
- Conditioned media were assessed for acute phase cytokines using bioassays and interleukin-6 concentrations via ELISA.
Main Results:
- Modified proteins, including proteolytically damaged alpha-1-antitrypsin and glycated albumin, stimulated macrophages to produce acute phase cytokines.
- This cytokine production was independent of polymyxin B, differentiating it from endotoxin-induced stimulation.
- The findings indicate that macrophages respond to specific protein modifications by releasing cytokines.
Conclusions:
- Proteolytically damaged proteins and end-glycosylation products formed in pathological conditions may induce cytokine release.
- These findings suggest a mechanism by which modified proteins contribute to circulating cytokines in diseases like acute inflammation and diabetes.
- Further research into protein modification pathways could offer insights into managing inflammatory and metabolic disorders.