The transmission of antibodies and normal γ -globulins across the young mouse gut

When 11-day mice are fed with homologous or heterologous antibodies or with heterologous $\gamma $-globulin, the maximum concentration of these proteins in their sera is reached 2 h later, irrespective of the amount or specificity of the proteins administered, or of the final concentration achieved. The relation between y (= relative titre of antibody, or concentration of heterologous $\gamma $-globulin, attained in the serum) and x (= dose of $\gamma $-globulin administered) is best represented by (a/y - b/x) = 1, a rectangular hyperbola with a theoretical maximum of y$_{\text{max.}}$ = a when x is very large. For any x, the proportion of y$_{\text{max.}}$ attained depends inversely on the value of b which is greatest for rat $\gamma $-globulin and then falls progressively for mouse anti-Salmonella pullorum agglutinins, bovine $\gamma $-globulin, guinea-pig $\gamma $-globulin, rabbit anti-Brucella abortus incomplete agglutinins, rat anti-Salm. pullorum agglutinins, rabbit $\gamma $-globulin and guinea-pig anti-Salm. pullorum agglutinins. The lower the value of b for any protein the less is the transmission of that protein affected by admixture with other $\gamma $-globulins, and if the protein is a $\gamma $-globulin, the more it reduces the transmission of antibodies or of other $\gamma $-globulins mixed with it. The value of b for rat anti-Salm. pullorum agglutinins is less than that for the corresponding normal $\gamma $-globulin. Fragment III of rabbit $\gamma $-globulin, prepared by the digestion method of Porter, is transmitted across the gut less readily than the intact molecule, but its ability to reduce the transmission of antibody is greater. These observations are consistent with the hypothesis of competitive absorption of ingested $\gamma $-globulin by a specific receptor within the absorptive cells of the gut. The receptor protects the attached protein from proteolysis and conveys it to the blood or lymph, possibly altered to a form more acceptable to the host.