The occurrence of macroglobulin antibodies in maternal and foetal sera of rabbits as determined by gradient centrifugation

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Abstract
Ultracentrifugation in a gradient of sucrose and subsequent fractionation has been used to determine the distribution of antibody activity between the heavy and light components of the immune sera of rabbits. The agglutinins to Brucella abortus in the sera of hyperimmune rabbits, which are transmitted readily to the foetuses, are in the light component and none are detectable in the macroglobulin. A macroglobulin component is present in the sera of rabbit foetuses of 22, 25 and 28 days of gestation and tends to increase with foetal age and to be more pronounced at 28 days than in the adult. The agglutinins to human red cells of Group A in rabbits immunized during pregnancy and killed on the 26th day of gestation are present in, and apparently confined to, the macroglobulin component of the foetal, as well as of the maternal, sera. This observation confirms the previous conclusion that agglutinins in both the heavy and light components of immune rabbit sera are transmitted readily from mother to foetus and that molecular size does not play an important part in the transmission of active immunity before birth in the rabbit.