TLR4 activation enhances the PD-L1-mediated tolerogenic capacity of colonic CD90+ stromal cells

Area of Science:

• Immunology
• Gastroenterology
• Cell Biology

Background:

• Programmed cell death ligand-1 (PD-L1) and PD-L2 signaling are vital for peripheral tolerance.
• CD90(+) myofibroblasts/fibroblasts (CMFs) in the colon express PD-1 ligands and suppress T cell proliferation.
• The role of Toll-like receptors (TLRs) in regulating PD-1 ligands on CMFs is unknown.

Purpose of the Study:

• To investigate if TLR signaling influences PD-1 ligand expression on human colonic CMFs.
• To determine the impact of TLR-induced PD-L1 upregulation on CMF-mediated immune suppression.
• To elucidate the signaling pathways involved in TLR-mediated PD-L1 regulation on CMFs.

Main Methods:

• Human CMFs were stimulated with TLR agonists.
• PD-L1 and PD-L2 expression was assessed via flow cytometry and qPCR.
• T cell proliferation and IFN-γ production were measured in co-culture assays.
• NF-κB, JAK2, and MyD88 signaling pathways were investigated.
• Fibroblast-specific MyD88 conditional knockout mice were used.

Main Results:

• TLR4 stimulation upregulated PD-L1, but not PD-L2, on human CMFs.
• TLR4-induced PD-L1 enhanced CMFs' suppression of CD4(+) T cell proliferation and IFN-γ production.
• PD-L1 upregulation was dependent on NF-κB, JAK2, and MyD88.
• MyD88-dependent TLR1/2 and TLR5 stimulation also increased PD-L1 expression.
• PD-L1 was decreased in MyD88-deficient mice, and its absence in CMFs increased mucosal IFN-γ.

Conclusions:

• MyD88-dependent TLR signaling on colonic CMFs upregulates PD-L1.
• This upregulation enhances CMFs' immunosuppressive function, contributing to mucosal tolerance.
• TLR-CMF-PD-L1 axis plays a role in maintaining intestinal immune homeostasis.