Immunogen |
C4 and C2 represent substrates for activated C1. Both components are present in serum in an inert form. C4 is composed of 3 polypeptide chains of three different types, , , . One of the chains is cleaved by the action of activated C1, resulting in activation of C4 exposing an binding site for the next component in the sequence, C2. C4 has a molecular weight of 205.000 and is present in plasma in an average concentration of 600 μg/ml. The activation of C4 yields two peptide fragments: C4a (MW 8,000) and C4b (MW 198,000). This process shows a considerable degree of similarity to the activation of the components C3 and C5. The C4 is isolated as a homogenous protein for use in antiserum production. Freund’s complete adjuvant is used in the first step of the immunization procedure. |