Ralph Ambrose Kekwick

Electrophoretic Analysis of the Sera of Young Rats

The absorption of maternal antibodies by the gut of the young rat continues for 20 days after birth and then ceases abruptly. The sera of rats at different ages during and after the absorptive period were examined electrophoretically and ultracentrifugally to determine the changes in the serum proteins during this period. The serum protein of rats of all age groups contained two albumin components (albumin1 and albumin2) and four globulin components (α1-, α2-, β- and γ-globulin), but the concentrations of these components, both relative and absolute, varied with age. The concentration of serum protein was considerably higher in mature than in suckling rats, due largely to a greater concentration of albumin. The amount of γ-globulin declined rapidly over the period 18 to 24 days of age, this decline paralleling that of the absorptive capacity of the gut of the young rat. The amount of β-globulin rose rapidly over this period. Conversely, between 24 and 40 days of age, the γ-globulin level rose and the β-globulin level declined. The changes in the α1- and α2-globulin were less marked but both declined over the period 18 to 30 days of age.

Electrophoretic studies of serum proteins of foetal rabbits

The sera of non-pregnant adult rabbits which had been hyperimmunized to Brucella abortus antigen, the sera of pregnant female rabbits which had not been immunized, and the sera, exocoelomic fluids, amniotic fluids and stomach contents of 25-day-old foetal rabbits were examined electrophoretically and ultracentrifugally. The serum of pregnant rabbits differed both in total protein concentration and in the proportions of the components from that of non-pregnant hyperimmunized rabbits. The foetal sera contained components corresponding to albumin, α-, β- and γ-globulin, but the proportions of these components, as well as the total protein concentrations, differed widely from those of the sera of both pregnant and non-pregnant adults. Foetal exocoelomic fluid, amniotic fluid and stomach contents contain similar electrophoretic components and resemble each other closely in the proportions of the components, though differing in the total concentrations. The components resemble those of sera in mobility, but the proportions of the components differ widely from those of the sera, both foetal and adult. Various experimental procedures to which rabbits were subjected resulted, after 24 h, in a significant increase in the total protein concentrations, without any corresponding change in the proportions of the components, of the foetal sera. No corresponding changes were detected in the maternal sera. The effect on the sera could be explained by withdrawal of water alone from the foetal circulation. Using antibodies as markers, it was shown that both β- and γ-globulin enter the foetal circulation from immune rabbit serum injected into the uterine lumen. The importance of the contribution of maternal serum proteins to the foetus is discussed in the light of the immunological and electrophoretic results.

The selection of antibodies by the gut of the young rat

The young of mother rats which had been immunized against Salmonella pullorum absorbed relatively much less antibody when they suckled during the period shortly after the initial immunization than during the period of hyperimmunity. After hyperimmunization against Brucella abortus both the maternal serum titres attained and the amounts of antibody reaching the young were similar to those of rats given a single immunizing injection of Salmonella pullorum. Antibodies from hyperimmune anti-SaZm. pullorum sera produced in a number of species of rodents and in rabbits, and from hyperimmune anti-Brucella abortus sera produced in rats, guinea-pigs and rabbits, when fed to young rats, were absorbed in amounts which were independent of the species in which the antisera were produced but related to the antigen used. The gut of the young rat was therefore showing a selection between antibodies produced in the same animal to the same antigen, the donor differing only in serum titre and length of the immunization period; and between antibodies produced in the same species to different antigens. The fractionation of antisera and titration of the fractions produced evidence that this selection of antibodies is related to their location in the serum proteins.