Inhibition of neutrophil function by fluid phase C3b of complement

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Abstract
A high-MW fragment of complement component C3 was isolated from normal human serum by column chromatography, was generated by incubation of serum at 37.degree. C with inulin and was produced from highly purified C3 by limited digestion with trypsin. This product inhibited the antibacterial function of neutrophils as shown by using Escherichia coli 075 as the main test organism. The inhibitor reacted with anti-C3b and anti-C3c, but not with anti-C3B (anti-native C3) or anti-C3a. The manner of preparation of the inhibitor, the sodium dodecyl sulfate-polyacrylamide gel electrophoresis pattern and the amino acid composition of the inhibitor indicated that it was fluid phase C3b. The inhibitor of neutrophil function (fluid phase C3b) bound to C3b receptors or acceptors on sheep erythrocytes in a model system.