[Localization of functionally important areas of the regulator protein factor H using monoclonal antibodies]

Four monoclonal antibodies to the control protein of the complement system, factor H, were used to try to localize functionally important domains on the molecule. Attempts to inhibit the interaction of C3b and H in ELISA and agglutination assays by means of these monoclonal antibodies showed that two of them, namely MAH 1 and MAH 2, recognized an epitope in close proximity to the binding site for C3b on H. The determinants defined by MAH 3 and MAH 4 are localized at a certain distance from this binding site, the MAH 4 epitope being situated closer to it than the MAH 3 epitope. The cofactor function of H with respect to C3b inactivator was inhibited by the same monoclonal antibodies which interfered with the binding of H to C3b. Since MAH 1, MAH 2, MAH 3 and MAH 4 all bind to the same tryptic 38 KD fragment of H, the binding site for C3b on H, as well as the cofactor activity seem to reside on this fragment.