STUDIES ON THE ANTIGENIC PROPERTIES OF COMPLEMENT

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Abstract
Antibodies against guinea pig complement (C) were produced by immunizing rabbits with either guinea pig serum globulin or with stromata of sensitized sheep erythrocytes laden with guinea pig complement, each in conjunction with Freund''s adjuvant. Agglutinating antibodies against guinea pig C fixed to sensitized sheep erythrocytes and precipitating antibodies against guinea pig serum were detectable in each of these types of rabbit immune serum absorbed with sensitized erythrocytes. Absorption of the immune sera with guinea pig serum removed both the agglutinins and precipitins. Sensitized erythrocytes exposed to heat-inactivated C'', to chelated C'', or to decomplemented guinea pig serum were not agglutinated by these immune sera. The rabbit anti-guinea pig C sera also showed low titers of agglutinins against sensitized erythrocytes exposed to human, rat, or horse C''. The antibodies when labelled with fluorescein isocyanate specifically stained sensitized erythrocytes exposed to C''. These studies show that C is antigenic in both the free and fixed forms. The anti-complement antibodies were precipitated by free C'' and were not present in normal rabbit serum or in sera of rabbits immunized with egg albumin or sensitized erythrocytes; the antibodies are, therefore, distinct from conglutinins.