Immune-inflammatory functions of fibroblasts

Inflammation is a response that has evolved over millions of years to become an extremely complex process. This complexity reflects the host's need to deal effectively with a wide variety of potentially injurious agents, as well as the need to incorporate an adequate set of checks and balances. An inappropriately checked response, which occurs rarely, results in disease, either acute or chronic. However, in most instances, inflammation is a beneficial response, essential for survival. Inflammation comprises an extensive network of cellular interactions implemented by an overwhelming number of molecules. One category of signal includes soluble products, such as neuropeptide, lipid mediators, cytokines and growth factors, most of which can be produced by inflammatory/haemopoietic cells. However, resident structural cells can also produce many of these products and, on this basis only, fibroblasts, epithelial, endothelial and smooth muscle cells should be considered as active contributors to the regulation of the inflammatory response. Extracellular matrix (ECM) proteins comprise another category of signals. Whilst the most recognized activities of these proteins are those concerned with providing structural tissue integrity, it is clear that they also have powerful inductive effects. Indeed, ECM proteins can influence the shape, movement and state of activation of inflammatory cells in the tissue. Recent evidence indicates that these signals may also play substantial roles in homing of inflammatory cells to certain sites and in the handling of a number of cytokines and growth factors. In so far as fibroblasts are the main producers of ECM proteins, these new data establish an indirect but important role for fibroblasts in the regulation of the inflammatory response.