C9 and factor B as acute phase proteins and their diagnostic and prognostic value in disease.

Some components of complement, such as C3, C9 and factor B, behave as acute phase reactants and their serum levels increase significantly in the course of inflammation. The diagnostic and prognostic significance of estimating the serum levels of C9 and factor B was evaluated in patients with Behçet's syndrome, recurrent oral ulceration and Crohn's disease, and the results were compared with those of measuring other acute phase reactants, such as C-reactive protein or alpha 1-antitrypsin. Longitudinal studies in these patients show a clear correlation between clinical indexes of the disease and levels of C9 and factor B. These findings, and experimental studies in monkeys, suggest that inflammation variously affects the synthesis of the acute phase reactants and that they play different roles as mediators of cellular damage.