Removal of Intravenously Injected Antigen by Circulating Precipitin

Abstract

Numerous investigators have reported that a specifically immunized animal eliminates intravenously injected antigen more rapidly than does a normal animal. 1 , 2 , 3 Evidence has been presented to show that the precipitin antibody is of importance in the disposition of the foreign material. 4 Virtually nothing has been established, however, as to whether the circulating or a fixed-tissue precipitin plays the major role in this elimination. The attempts to determine the relative importance of the circulating precipitin and the fixed-tissue precipitin in the removal of the injected antigen have been hindered by the lack of suitable methods for quantitatively estimating this antibody in an antiserum. Recently, we 5 proposed a procedure, which we called the “neutralization method,” for quantitatively titrating the precipitin against crystalline egg albumin. This method seems to overcome the difficulty in estimating precipitin and appears advantageous for investigating the relative importance of the circulating and fixed-tissue antibody in eliminating antigen.

We have been able by the neutralization method to determine quantitatively the effect on the circulating precipitin of the intravenous injection of antigen into an immunized rabbit. The amount of antibody, expressed in milligrams of nitrogen per cc. of the serum, present just before and one hour after injecting a known amount, in milligrams of nitrogen, of crystalline egg albumin has been found experimentally. The total circulating precipitin of the rabbit has been calculated by multiplying the amount of precipitin determined per cc. of serum by the number of cc. in the animal's plasma volume. The plasma volume has been considered, from determinations we have recently offered, 6 to approximate 3.4% of the body weight of the rabbit. Data, suggesting the essential importance of the circulating precipitin in removing the intravenously injected antigen, are presented in Table I for 8 rabbits of a longer series studied in this regard.