Antibody-Opsonized Bacteria Evoke an Inflammatory Dendritic Cell Phenotype and Polyfunctional Th Cells by Cross-Talk between TLRs and FcRs

Abstract

During secondary immune responses, Ab-opsonized bacteria are efficiently taken up via FcRs by dendritic cells. We now demonstrate that this process induces cross-talk between FcRs and TLRs, which results in synergistic release of several inflammatory cytokines, as well as altered lipid metabolite profiles. This altered inflammatory profile redirects Th1 polarization toward Th17 cell responses. Interestingly, GM-CSF–producing Th cells were synergistically evoked as well, which suggests the onset of polyfunctional Th17 cells. Synergistic cytokine release was dependent on activation via MyD88 and ITAM signaling pathways through TLRs and FcRs, respectively. Cytokine regulation occurred via transcription-dependent mechanisms for TNF-α and IL-23 and posttranscriptional mechanisms for caspase-1–dependent release of IL-1β. Furthermore, cross-talk between TLRs and FcRs was not restricted to dendritic cells. In conclusion, our results support that bacteria alone initiate fundamentally different immune responses compared with Ab-opsonized bacteria through the combined action of two classes of receptors and, ultimately, may refine new therapies for inflammatory diseases.

Cross‐talk between pathogen recognizing Toll‐like receptors and immunoglobulin Fc receptors in immunity

“…In contrast, DCs stimulated with either TLR ligands or (complexed) IgG do not induces significant TNFα or IL‐23 release. This is in accordance with low mRNA transcription levels of these cytokines after binding to either TLRs or FcγRs .…”

“…Functional cross‐talk between cell surface‐expressed TLRs and FcRs does not require internalization as blocking internalization of IgG‐opsonized S. aureus with the actin‐polymerization inhibitor, cytochalasin, did not abrogate production of inflammatory cytokines (TNFα, IL‐1β, IL‐6, and IL‐23) . Similarly, when large IgG‐coated beads (too large to phagocytose) were used to stimulate DCs in combination with ligands for the cell surface‐expressed TLR 2, 4, or 5, enhanced cytokine production was still observed . Combining IgG‐coated beads with ligands for the intracellular TLR7/8 also induced synergistic release of TNFα , which further suggest that triggering of both type of receptors is sufficient to induce an inflammatory response, even in the absence of phagocytosis.…”

“…Intriguingly, only DCs that were simultaneously activated via TLRs and FcγRs mediated both production and release of the mature IL‐1β. This observation was strengthened by the finding that blocking FcγRII (with whole antibody, clone AT10 recognizing both FcγRIIa and FcγRIIb) during co‐activation did not affect pro‐IL‐1β mRNA levels, but inhibited extracellular release of mature IL‐1β . Thus, cross‐talk between TLRs and FcRs is an additional mechanism to control release of inflammatory mediators during re‐infection with a harmful pathogen.…”

Antibody opsonization enhances MAIT cell responsiveness to bacteria via a TNF‐dependent mechanism

“…In murine macrophages, FcγR‐mediated stimulation of MAPK pathways, particularly the activation of p42 MAPK (also known as ERK2) results in TNF synthesis . Furthermore, antibody‐opsonization of bacteria triggered toll‐like receptor signaling pathways through FcγR resulting in upregulation of various cytokines, including TNF in human dendritic cells . Thus, IgG‐opsonization of bacteria results in enhanced phagocytosis supporting both MR1‐presentation and an elevated production of TNF by monocytes, which in turn results in more efficient activation of MAIT cells.…”

“…Next, we investigated whether the enhanced MAIT cell activation by IgG‐opsonization was due to a better association of E. coli with different cell populations relevant for MAIT cell activation in PBMCs. We took advantage of previously described protocols used to measure bacterial uptake of FITC‐ or CFSE‐labeled bacteria (Supplementary figure 2a). Using CFSE‐labeled E. coli we found that the presence of hiNHS or Intratect increased the association of bacteria with PBMCs (Supplementary figure 2b).…”