Macrophage LTB4 drives efficient phagocytosis of Borrelia burgdorferi via BLT1 or BLT2

Yan Zhang,Rachel M Olson,Charles R Brown

doi:10.1194/jlr.m068882

Abstract

Unresolved experimental Lyme arthritis in C3H 5-lipoxygenase (5-LOX)-/- mice is associated with impaired macrophage phagocytosis of Borrelia burgdorferi In the present study, we further investigated the effects of the 5-LOX metabolite, leukotriene (LT)B4 on phagocytosis of B. burgdorferi Bone marrow-derived macrophages (BMDMs) from 5-LOX-/- mice were defective in the uptake and killing of B. burgdorferi from the earliest stages of spirochete internalization. BMDMs from mice deficient for the LTB4 high-affinity receptor (BLT1-/-) were also unable to efficiently phagocytose B. burgdorferi Addition of exogenous LTB4 augmented the phagocytic capability of BMDMs from both 5-LOX-/- and BLT1-/- mice, suggesting that the low-affinity LTB4 receptor, BLT2, might be involved. Blocking BLT2 activity with the specific antagonist, LY255283, inhibited phagocytosis in LTB4-stimulated BLT1-/- BMDMs, demonstrating a role for BLT2. However, the lack of a phagocytic defect in BLT2-/- BMDMs suggested that this was a compensatory effect. In contrast, 12(S)-hydroxyheptadeca-5Z,8E,10E-trienoic acid, a natural BLT2-specific high-affinity ligand, and resolvin E1, a BLT1 agonist, were both unable to boost phagocytosis in BMDMs from either 5-LOX-/- or BLT1-/- mice, suggesting a specific role for LTB4 in mediating phagocytosis in murine macrophages. This study demonstrates that LTB4 promotes macrophage phagocytosis of bacteria via BLT1, and that BLT2 can fulfill this role in the absence of BLT1.

Highlights

Unresolved experimental Lyme arthritis in C3H 5-lipoxygenase (5-LOX) / mice is associated with impaired macrophage phagocytosis of Borrelia burgdorferi
Because we previously demonstrated an exacerbated and prolonged Lyme arthritis in B. burgdorferi-infected 5-LOX / mice that was associated with impaired phagocytosis in mouse leukocytes [22], we further assessed the role of 5-LOX / metabolites in mediating macrophage phagocytosis
WT bone marrow-derived macrophage (BMDM) were capable of the efficient uptake and destruction of B. burgdorferi spirochetes, with degraded organisms colocalizing with LAMP1-containing phagolysosomes (Fig. 1A)

Summary

Introduction

Unresolved experimental Lyme arthritis in C3H 5-lipoxygenase (5-LOX) / mice is associated with impaired macrophage phagocytosis of Borrelia burgdorferi. Blocking BLT2 activity with the specific antagonist, LY255283, inhibited phagocytosis in LTB4-stimulated BLT1 / BMDMs, demonstrating a role for BLT2. 12(S)-hydroxyheptadeca5Z,8E,10E-trienoic acid, a natural BLT2-specific high-affinity ligand, and resolvin E1, a BLT1 agonist, were both unable to boost phagocytosis in BMDMs from either 5-LOX / or BLT1 / mice, suggesting a specific role for LTB4 in mediating phagocytosis in murine macrophages. We have previously demonstrated that infection of WT C3H/HeJ mice with Borrelia burgdorferi induced the production of numerous pro- and anti-inflammatory lipid mediators in their heart and joint tissues [18]. B. burgdorferi infection increased the expression of 5-LOX in joint tissues and induced the production of several 5-LOX metabolites, including LTB4 [18].

Methods

Results

Conclusion