Antibodies reactive with the homologous antigens (A-R-HSA and G-R-HSA) as well as with denatured DNA were produced in rabbits by immunization with nucleoside-protein conjugates. In C′ fixation, these sera reacted with the homologous antigens more efficiently when incubation was carried out at 4°C than at 37°C. The C′ fixation reaction of these sera with denatured DNA was not markedly affected by the temperatures of incubation. Upon separation of the serum proteins by Sephadex G-200 it was found that the antibodies reactive with the homologous antigens were contained in Fraction II (7S fraction) and the antibodies in this fraction reacted with greater efficiency at 4°C than at 37°C. Both Fractions I (19S) and II (7S) reacted with denatured calf thymus DNA. With DNA, Fraction I exhibited C′ fixing activity only after incubation at 37°C whereas C′ fixation of Fraction II was much greater at 4°C than at 37°C. Treatment with 0.1 M mercaptoethanol had little effect on the C′ fixing reaction of the serum with A-R-HSA at 4°C or with DNA at 4°C. However, a marked decrease in the ability to fix C′ occurred when DNA was utilized as the antigen and incubation was carried out at 37°C. These studies therefore indicate the production of 19S antibodies reactive with DNA at 37°C and the production of 7S antibodies reactive with both the homologous antigen and with DNA at 4°C. Inhibition of the whole serum and denatured DNA occurred with a much lower level of adenosine at 4°C than when an incubation period at 37°C was employed. Inhibition of the fractions demonstrated that Fraction II at 4°C was inhibited with lower concentrations of adenosine than was Fraction I at 37°C, and adenosine in both cases produced greater inhibition than did the other nucleosides.

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