Figure 4.

Central role of immune acting fibroblasts in innate immunity. Barrier tissue fibroblasts are tissue-resident sentinel cells, and some orchestrate innate immune responses. Following epithelial damage and breach by bacterial, viral, or parasitic pathogens, fibroblasts recognize threats directly through pattern recognition receptors (i.e., TLRs) and receive proinflammatory cytokine danger signals (i.e., TNFα) from epithelial cells and tissue-resident lymphoid and myeloid cells (black lines). Upon activation by these innate immune stimuli, committed preadipocyte fibroblasts differentiate into adipocytes (solid red line) and elicit critical immune effector functions for pathogen elimination (faded red lines) including direct antimicrobial activity, leukocyte recruitment, and activation of epithelial cells and tissue-resident leukocytes. This figure models the role fibroblasts play in innate immunity at barrier tissue sites and is not meant to suggest that each fibroblast subtype and state across tissues is known to perform all functions depicted.