Regulation of macrophage activity by surface receptors contained within Borrelia burgdorferi-enriched phagosomal fractions

Abstract

Macrophages mediate the elimination of pathogens by phagocytosis resulting in the activation of specific signaling pathways that lead to the production of cytokines, chemokines and other factors. Borrelia burgdorferi, the causative agent of Lyme disease, causes a wide variety of pro-inflammatory symptoms. The proinflammatory capacity of macrophages is intimately related to the internalization of the spirochete. However, most receptors mediating this process are largely unknown. We have applied a multiomic approach, including the proteomic analysis of B. burgdorferi-containing phagosome-enriched fractions, to identify surface receptors that are involved in the phagocytic capacity of macrophages as well as their inflammatory output. Sucrose gradient protein fractions of human monocyte-derived macrophages exposed to B. burgdorferi contained the phagocytic receptor, CR3/CD14 highlighting the major role played by these proteins in spirochetal phagocytosis. Other proteins identified in these fractions include C-type lectins, scavenger receptors or Siglecs, of which some are directly involved in the interaction with the spirochete. We also identified the Fc gamma receptor pathway, including the binding receptor, CD64, as involved both in the phagocytosis of, and TNF induction in response to B. burgdorferi in the absence of antibodies. The common gamma chain, FcγR, mediates the phagocytosis of the spirochete, likely through Fc receptors and C-type lectins, in a process that involves Syk activation. Overall, these findings highlight the complex array of receptors involved in the phagocytic response of macrophages to B. burgdorferi.

A combined transcriptomic approach to identify candidates for an anti-tick vaccine blocking B. afzelii transmission

“…For instance, macrophage 1 antigen, more recently known as complement receptor 3 (CR3), is an integrin present on polymorphonuclear leukocytes and binds fibrinogen which leads to macrophage adhesion and activation. Interestingly, CR3 interacts with uPAR, which has been shown to be important for the clearance of Borrelia and CR3 also binds Borrelia directly to polymorphonuclear leukocytes 28,[46][47][48][49] . As the ligands of most ixodegrins are currently unknown, it might be possible that some could protect Borrelia from the host's immune response.…”

Borrelia burgdorferi infection induces long-term memory-like responses in macrophages with tissue-wide consequences in the heart

“…The surface expression levels of CD11b [39][40][41] were higher in previously stimulated cells, compared to unexposed controls ( Fig 3E), which could be observed at the gene expression level (Itgam, Fig 3F). We also found increased expression levels of genes involved in the binding of B. burgdorferi to macrophages [42], including Marco, Cd302 (encoding the receptor CLEC4B1), Clec4n, Clec4d, and Msr1, while Siglecf (encoding the receptor Siglec5) https://doi.org/10.1371/journal.pbio.3001062.g003…”

“…In order to analyze the internalization rate of the spirochete independently of the binding capacity of the cells, we compared the phagocytic index [42] of macrophages previously stimulated with the spirochete and unstimulated cells. This analysis revealed similar internalization rates for B. burgdorferi (Fig 3H), indicating that the higher internalization observed in macrophages previously activated was due to the increased ability of these cells to bind the bacterium rather than an augmented capacity to internalize the spirochete once bound to the cell.…”

Specific Integration of Temperate Phage Decreases the Pathogenicity of Host Bacteria

“…RAW264.7 cells were cultured in a six-well plate with RPMI 1640 medium (HyClone, USA) containing 10% (v/v) fetal bovine serum (Gibco, USA) as described previously (Carreras-Gonzalez et al, 2019). The cells were washed three times with PBS before adding exponential-phase Bb01 or Bb01+ cells at a ratio of 10:1 (B. bronchiseptica to RAW264.7).…”