Activation of the properdin pathway of complement in patients with gram-negative bacteremia.

To determine the pathway used for activation of complement component C3, serum levels of components C1, C4, C2, C3, C5, C6, and C9 and two properdin factors, properdin and factor B, were measured in 42 patients with gram-negative bacteremia, in 19 of whom shock subsequently developed. Mean levels of the classical components C1, C4, and C2 in bacteremic patients in whom shock subsequently developed did not differ significantly (p greater than 0.05) from those of patients with uncomplicated bacteremia. Levels of properdin, factor B and C3, C5, C6, and C9 were significantly (p less than 0.05) decreased in patients with shock in comparison with those with uncomplicated bacteremia. Taken together, these findings are consistent with activation of C3 and the terminal complement sequence, C5-C9, occurring primarily by the properdin pathway, in patients with gram-negative bacteremia eventuating in shock. Biologically active products released during activation of C3-C9 may contribute to the development of shock.