The innate immune system is a generic response to infection or injury. Evidence shows the innate response has immunological memory capable of altering subsequent responses to stimuli. Fibroblasts are ubiquitous stromal cells capable of responding to inflammatory triggers, and of orchestrating endothelial cell and leukocyte behaviour during inflammation. Repeated challenge with cytokines (such as tumour necrosis factor (TNF) a) induced an augmented second response to stimulation. Fibroblasts from multiple anatomical locales significantly increased cytokine secretion upon second challenge with TNFa. The precise mediators augmented depended on fibroblast site of origin. Depending on site, memory was inherent, or only present in fibroblasts from chronically-inflamed tissue. This suggests a phenomenon intrinsic to some sites but pathological in others. The secreted mediators from the fibroblast initial or memory responses exerted differing effects on leukocytes, dependent upon fibroblast site of origin. Finally, examination of intracellular signalling showed the augmented response was at least partly due to prolonged activity of nuclear factor (NF) KB during the memory response. Innate immune memory exists in fibroblasts from multiple tissues, but may be pathologically acquired in some. The altered response to second challenge may represent a fibroblast mechanism for altering the recruitment and behaviour of the inflammatory infiltrate.
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