The inflammatory process is a response to many different kinds of tissue injury. One event thay may be common to many apparently unrelated irritants is the deposition of fibrin. Three experimental designs have considered the significance of fibrin in acute inflammation, but only the third will be discussed extensively (details of the other approaches have been published). In the first approach, the biochemical profile of proteins concerned in fibrin formation was defined quantitatively for inflammatory fluids obtained from acutely inflamed joints of humans with arthritic diseases. Quantitative differences appeared to reflect degress of inflammation rather than to define a profile unique for the types of arthritis. The second experimental approach attempted to correlate the type of exudative leucocytes with the presence of fibrin in human joint disease and experimental skin windows on dogs. The granulocyte phase of inflammation was maintained and prolonged by the presence of fibrin. The third experimental approach was a quantitative study of leucocyte response to the chemotactic power of fibrin, fibrinogen, and their proteolysis products. By a skin window collection chamber technique with dogs, the leucocyte responses to fibrin-related material. other protein aggregates (albumin, γ-globulin, antigen-antibody complexes), and several inert particulate or structured preparations were compared. Fibrin-related materials were the most potent chemotactic agents for granulocyte (predominantly neutrophil) emigration in acute inflammation.
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