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Bone marrow granulocytes downregulate IL-1β and TNF production and the microbicidal activity of inflammatory
Renata Novaes1,2, Tatiana F R Costa1, Amy L Goundry1
1Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21941-971, Brazil.
Abstract:
Macrophages play critical roles in inflammation and defense against pathogens, as well as in the return to tissue homeostasis. Macrophage subpopulations displaying antagonistic phenotypes are generally classified as proinflammatory M1, implicated in antipathogen and antitumoral activities, or as anti-inflammatory M2, associated with tissue repair. Granulocytic and monocytic myeloid-derived suppressor cells recruited from the bone marrow to tissues and phagocytosis of apoptotic neutrophils can attenuate macrophage microbicidal activity. Here, we showed that bone marrow neutrophils, but not thioglycollate-recruited neutrophils, directly suppress the responses of macrophages that were previously committed to an inflammatory phenotype. Cocultures of inflammatory macrophages with bone marrow CD11b+Ly6Ghi granulocytes led to reduced release of IL-1β, TNF-α, and IL-6 by macrophages after lipopolysaccharide stimulation. The suppressive activity was unrelated to granulocyte apoptosis or to secreted factors and required cell-to-cell contact. The suppressive effect was paralleled by reduction in the nuclear levels of the NF-κB p65 subunit, but not of the p50 subunit. Furthermore, bone marrow granulocytes decreased the phagocytic activity of macrophages and their capacity to kill intracellular Escherichia coli. Taken together, these results show that bone marrow granulocytes can function as suppressors of the proinflammatory activity and microbial-killing responses of macrophages.
Insights
Bone marrow granulocytes, but not those from other tissues, suppress inflammatory macrophages. This cell-to-cell interaction reduces cytokine release and impairs the killing of bacteria by macrophages.
Area of Science:
- Immunology
- Cell Biology
Background:
- Macrophages are key immune cells with distinct M1 (proinflammatory) and M2 (anti-inflammatory) phenotypes.
- Myeloid-derived suppressor cells and neutrophil apoptosis can dampen macrophage activity.
- The specific role of bone marrow neutrophils in modulating macrophage function requires further elucidation.
Purpose of the Study:
- To investigate the direct effect of bone marrow granulocytes on inflammatory macrophage responses.
- To determine the mechanisms by which bone marrow granulocytes suppress macrophage activity.
Main Methods:
- Coculture of inflammatory macrophages with bone marrow CD11b+Ly6Ghi granulocytes.
- Lipopolysaccharide (LPS) stimulation of macrophages.
- Measurement of cytokine release (IL-1β, TNF-α, IL-6) via ELISA.
- Analysis of NF-κB p65 and p50 nuclear translocation via Western blot.
- Assessment of macrophage phagocytic activity and intracellular bacterial killing (Escherichia coli).
Main Results:
- Bone marrow granulocytes significantly reduced the release of IL-1β, TNF-α, and IL-6 by LPS-stimulated macrophages.
- This suppression required direct cell-to-cell contact and was independent of granulocyte apoptosis or secreted factors.
- Bone marrow granulocytes decreased nuclear levels of the NF-κB p65 subunit in macrophages.
- Phagocytic capacity and intracellular killing of Escherichia coli by macrophages were diminished in the presence of bone marrow granulocytes.
Conclusions:
- Bone marrow granulocytes directly suppress the proinflammatory and microbicidal functions of inflammatory macrophages.
- Cell-to-cell contact-dependent mechanisms involving NF-κB signaling are implicated in this suppression.
- These findings reveal a novel regulatory role for bone marrow granulocytes in modulating innate immune responses.
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