The first component of the human complement system recognizes the active fraction of heparin.

A low molecular weight heparin fraction with high anticoagulant activity was isolated from the precipitate of the interaction with the first component of the human complement system. Our results confirmed the predictions: under very strict conditions of pH (6.3), CaCl2 concentration (2 mM), ionic strength (25 mM) and protein/heparin ratio (1/1), the first component of the complement recognizes the high antithrombin III affinity fraction of heparin, and allows a concentration of the biological activity of the original low molecular weight-heparin.