A binding activity of actin with human C1q

A direct interaction of actin with C1q was demonstrated by two in vitro assays using purified human C1q and actins from rabbit skeletal muscle, chicken gizzard muscle and ascaris body wall. Every actin gave rise to a precipitation line with human C1q in agarose gel diffusion. A direct binding of actin with human C1q was ascertained by a binding assay system using radio-labelled rabbit actin and paper discs coated with human C1q. This binding of rabbit actin to C1q was inhibited by addition of unlabelled homologous and heterologous actins in the assay system. Results indicated that such interactions of actins with the human C1q were beyond species specificity.