Rabbit Antibodies Induced by Calf Thymus Histone-Serum Albumin Complexes

Summary Antibodies that react in C′ fixation with calf thymus histone determinants have been produced in two rabbits by immunization with whole histone coupled to human serum albumin with a carbodiimide reagent. The sera containing these antibodies reacted directly with the coupled whole histone (whole histone-HSA) and with the histone fractions coupled to HSA. The sera did not react directly with free whole histone, but both unconjugated histone and the fractions inhibited the reaction with coupled histone. Slight direct reactivity was observed with protamine-HSA. The histone-HSA did not react with either a nonimmune serum or an unrelated immune serum, and the free whole histone did not inhibit the reaction of an unrelated antigen-antibody system. In direct reactions with the conjugated histone fractions, the greatest reactivity occurred with F1(A)-HSA, followed by F2b-HSA, Fw-HSA, and F2a-HSA. This same order of effectiveness of the free fractions was observed in inhibition of the reaction of this serum with whole histone-HSA. Fraction F1(A) was also the most effective inhibitor of the reaction with any of the coupled fractions. The order of direct reactivity with the coupled fractions and inhibition by the free fractions each paralleled the lysine-arginine ratios of these fractions but not those of the whole histone preparation. Other basic polypeptides such as polylysine (MW 100,000), poly-arginine, and methylated bovine serum albumin also inhibited this system but failed to inhibit a nonrelated C′-fixing immune system. Monomeric lysine and arginine neither inhibited nor reacted directly when conjugated to HSA.