C1q-binding proteins and C1q receptors

Aggregated or immobilized complement Clq induces cellular responses in many different cell types. Clq-induced cellular responses may be involved in ho st defense and in protection against autoimmunity because C1 q-deficient hu mans have infectious complications and a very high incidence of autoimmune disease. The search for the Clq receptor(s), which has been ongoing for 25 years. has led recently to the recognition that proteins identified as bind ing to C1q may be divided into two groups: Clq-binding molecules that are n ormally intracellular; and cell surface Clq receptors.