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Monocyte aggregation and superoxide anion release in response to formyl-methionyl-leucyl-phenylalanine (FMLP) and
Abstract:
Like the PMN, human peripheral blood monocytes were capable of aggregating in response to FMLP and PAF. Monocyte aggregation was dependent on glycolysis and the presence of divalent cations. Unlike the PMN, monocyte aggregation in response to FMLP was not accompanied by degranulation, nor was it potentiated by cytochalasin B. Furthermore, cytochalasin B and its cogenitor, dihydrocytochalasin B, inhibited aggregation in response to PAF. PAF and FMLP appeared to react with the monocyte at separate receptors because sequential challenge of the monocyte with the same agents failed to elicit further aggregation, whereas rechallenge with the alternative agent induced further aggregation. Because the monocyte will aggregate to chemotactic agents in vitro, it is likely that the cell will be affected by these agents in vivo, which could lead to leukoembolization of circulating monocytes.
Insights
Human monocytes aggregate in response to FMLP and PAF, requiring glycolysis and divalent cations. Unlike neutrophils, monocytes do not degranulate with FMLP, and cytochalasin B inhibits PAF-induced aggregation.
Area of Science:
- Immunology
- Cellular Biology
Background:
- Human peripheral blood monocytes, like polymorphonuclear neutrophils (PMNs), can aggregate in response to chemotactic factors.
- Understanding monocyte aggregation mechanisms is crucial for comprehending inflammatory and immune responses.
Purpose of the Study:
- To investigate the mechanisms of human monocyte aggregation induced by N-formyl-methionyl-leucyl-phenylalanine (FMLP) and platelet-activating factor (PAF).
- To compare monocyte aggregation responses to those of PMNs and to explore the roles of glycolysis, divalent cations, and specific inhibitors.
Main Methods:
- Monocyte aggregation assays were performed using FMLP and PAF as stimuli.
- Experiments assessed the dependence on glycolysis and divalent cations.
- The effects of cytochalasin B and dihydrocytochalasin B on aggregation were evaluated.
- Sequential challenges with FMLP and PAF were used to investigate receptor interactions.
Main Results:
- Monocyte aggregation was dependent on glycolysis and divalent cations.
- Unlike PMNs, FMLP-induced monocyte aggregation did not involve degranulation and was not enhanced by cytochalasin B.
- Cytochalasin B and dihydrocytochalasin B inhibited PAF-induced monocyte aggregation.
- Evidence suggests distinct receptors for PAF and FMLP on monocytes, as indicated by sequential challenge experiments.
Conclusions:
- Human monocytes exhibit distinct aggregation mechanisms compared to PMNs.
- Monocyte aggregation is a metabolically dependent process influenced by divalent cations.
- The findings suggest potential in vivo implications for monocyte aggregation, including leukoembolization.