Chemotactic factor inactivator in normal human serum.

Normal human serum contains an inactivator of chemotactic factors for neutrophilic leukocytes. The chemotactic factor inactivator (CF-I) remains soluble when serum is fractionated with ammonium sulfate (at 45% saturation), directly and irreversibly inactivates chemotactic factors, and it has a broad spectrum of activity as indicated by its inactivation of the chemotactic fragments of human C3 and C5 (third and fifth components of complement), C567, and the bacterial chemotactic factor derived from Escherichia coli. CF-I appears as a biphasic activity according to preparative techniques of sucrose density ultracentrifugation, electrophoresis, and gel filtration. Studies on the interaction of CF-I with the radiotagged C5 chemotactic fragment fail to reveal evidence for irreversible binding as the basis for inactivation. CF-I varies from the anaphylatoxin inactivator in several physical-chemical respects, but evidence does not permit a conclusive statement about the relationship of the two inactivators. CF-I may function as a regulator of inflammatory responses.