Short-Term Regulation of FcγR-Mediated Phagocytosis by TLRs in Macrophages: Participation of 5-Lipoxygenase Products

Abstract EN

TLRs recognize a broad spectrum of microorganism molecules, triggering a variety of cellular responses.

Among them, phagocytosis is a critical process for host defense.

Leukotrienes (LTs), lipid mediators produced from 5-lipoxygenase (5-LO) enzyme, increase FcγR-mediated phagocytosis.

Here, we evaluated the participation of TLR2, TLR3, TLR4, and TLR9 in FcγR-mediated phagocytosis and whether this process is modulated by LTs.

Rat alveolar macrophages (AMs), murine bone marrow-derived macrophages (BMDMs), and peritoneal macrophages (PMs) treated with TLR2, TLR3, and TLR4 agonists, but not TLR9, enhanced IgG-opsonized sheep red blood cell (IgG-sRBC) phagocytosis.

Pretreatment of AMs or BMDMs with drugs that block LT synthesis impaired the phagocytosis promoted by TLR ligands, and TLR potentiation was also abrogated in PMs and BMDMs from 5-LO−/− mice.

LTB4 production induced by IgG engagement was amplified by TLR ligands, while cys-LTs were amplified by activation of TLR2 and TLR4, but not by TLR3.

We also noted higher ERK1/2 phosphorylation in IgG-RBC-challenged cells when preincubated with TLR agonists.

Furthermore, ERK1/2 inhibition by PD98059 reduced the phagocytic activity evoked by TLR agonists.

Together, these data indicate that TLR2, TLR3, and TLR4 ligands, but not TLR9, amplify IgG-mediated phagocytosis by a mechanism which requires LT production and ERK-1/2 pathway activation.