Antigenic identification of chemotactic factor inactivator in normal human serum and bronchoalveolar lavage fluid

Several proteins have been described that can modulate the activity of the complement component C5a, a potent chemoattractant for neutrophils. One of these inhibitors has been termed chemotactic factor inactivator (CFI). We hypothesized that CFI was antigenically present in normal human serum and that antigenic levels would correlate with the ability of serum to inhibit C5a. To test this hypothesis, CFI was purified from normal human serum, antibodies to CFI were developed in rabbits, and these reagents were used to develop an enzyme-linked immunoadsorbent assay to measure CFI. Sera from 32 normal volunteers were assayed for CFI and found to contain 77 ± 29 μg/ml (range 17 to 137 μg/ml). Partially purified CFI from normal human sera was found to inhibit 61% ± 9% (range 45% to 75%) of the ability of C5a to attract human neutrophils. Importantly, the ability of CFI to inhibit C5a-induced neutrophil chemotaxis correlated with the antigenic amounts of CFI (r = 0.68, P < 0.05), suggesting that CFI is a major inhibitor of C5a. This was confirmed by the finding that (1) all C5a inhibitory activity coprecipltated with CFI by ammonium sulfate precipitation (45% to 65% saturation), and (2) depletion of this ammonium sulfate fraction of CFI resulted in a major loss in its ability to inhibit the chemotactic activity of C5a (57% vs. 8% inhibition, P < 0.01). To determine whether CFI could play a role in the modulation of inflammation at tissue sites, normal bronchoalveolar lavage fluid was evaluated for the presence of CFI. CFI was identified in all fluids (mean 0.50 ± 0.09 μg/mg albumin, range 0.14 to 1.43 μg/mg albumin). The above data suggest that CFI is antigenically and functionally present in normal human serum and bronchoalveolar lavage fluid and may be an important inhibitor of C5a-induced neutrophil chemotaxis in tissues.