Nephelometric determination of rat fibrinogen as a marker of inflammatory response

Following tissue injury or infection, the concentrations of several plasma proteins are altered substantially. The characteristic pattern of this change is termed the acute phase response, and can be observed in many different inflammatory situations, including surgical trauma, injury, infections, tissue infarction and several immunologically mediated states such as temporalis arteritis, polymyalgia rheumatica and rheumatoid arthritis. It is often of great clinical value to monitor the acute phase response in humans but the assays used to measure the acute response in man (e.g., erythrocyte sedimentation rate and C-reactive protein) is less well suited for experimental studies in the rat. We have instead developed a nephelometric assay for determination of fibrinogen as a marker of the inflammatory response in rats. The assay was used to monitor the inflammatory response in type II collagen arthritis in rats. This model involves the induction of severe polyarthritis and is a widely used animal model for rheumatoid arthritis (RA). Fibrinogen concentrations increased from 3.1 g/l before immunization to 10.5 g/l 2 weeks after the immunization, after which they gradually declined towards normal levels. This pattern of fibrinogen alterations correlated well with the inflammatory phase of the arthritic response. Plasma fibrinogen may thus represent a rapid and sensitive marker of the acute phase response in the rat.