Monoclonal Antibodies to Complement Components Without the Need of Their Prior Purification. I. Antibodies to Mouse C1q

Rat monoclonal antibodies (MAbs) reactive with mouse complement subcomponent C1q were raised applying a principle that requires minute amounts of serum and circumvents purification of serum-derived C1q. The principle involves a) using the high affinity of certain cell-bound antibody isotypes for intercalating C1q from serum of various species, b) selecting such antibodies as are syngeneic to the immunized animal species, thus avoiding the production of antibodies against the intercalating antibodies and c) screening for the anti-C1q MAb in microtiter plates coated with C1q-intercalating MAb isotypes that are heterogeneic to the immunized animal species. We could establish 3 MAbs of IgM subclass, whose reactivity to mouse C1q was shown by ELISA techniques. One of them (RmC13C9) crossreacted with human C1q and was shown by SDS-PAGE and subsequent immunoblotting to recognize the C-chain of mouse and human C1q. The other two MAbs are directed against SDS-sensitive epitopes on mouse C1q and were, therefore, further characterized by native agarose gel electrophoresis and immunohistochemical studies.