A substance-conjugated complement component C1q is provided. A substance such as signal emitting substances or cell function regulating substances is conjugated via a sulfur atom to at least one site of the component. The site is not involved in binding immunoglobulins. A marker-labelled complement component C1q is used for measuring a complement-binding antibody, an antigen, a neutralizing antibody or a substance produced internally of and at the surface of a cell or a microorganism by measuring the marker.
展开▼
