PD-L1 expression on tolerogenic APCs is controlled by STAT-3.

Area of Science:

• Immunology
• Cell Biology

Background:

• Toll-like receptor (TLR) agonists modulate innate immune cell responses during infection.
• Conventional differentiation of monocytes into immature dendritic cells (iDCs) can be blocked by early TLR agonist exposure, leading to a distinct phenotype.

Purpose of the Study:

• To investigate the characteristics of antigen-presenting cells (APCs) generated by TLR agonist exposure during dendritic cell (DC) differentiation.
• To elucidate the regulatory mechanisms underlying programmed death-ligand 1 (PD-L1) expression on these modified APCs and their impact on T cell responses.

Main Methods:

• Monocyte differentiation into iDCs was assessed in the presence of TLR agonists (R848, LPS).
• Flow cytometry was used to analyze cell surface markers (CD14, CD1a, PD-L1).
• T cell proliferation assays were performed. Cytokine levels (IL-6, IL-10) and signaling pathways (MAPK, STAT-3) were investigated, including STAT-3 binding to the PD-L1 promoter via chromatin immunoprecipitation.

Main Results:

• TLR agonists induced a deviated APC phenotype (TLR-APCs) characterized by retained CD14 and absent CD1a expression, along with PD-L1 expression.
• TLR-APCs failed to induce T cell proliferation and promoted the development of T regulatory cells (Tregs).
• PD-L1 expression was dependent on STAT-3 activation, which was modulated by MAPK signaling pathways through the production of IL-6 and IL-10. STAT-3 directly bound to the PD-L1 promoter.

Conclusions:

• TLR agonists induce a tolerogenic APC phenotype during DC differentiation.
• STAT-3 plays a pivotal role in regulating PD-L1 expression on these APCs.
• The MAPK/cytokine/STAT-3 pathway mediates the induction of PD-L1 and the development of tolerogenic APCs.