Molecular characterization of the antibody response in rabbits to intravenously injected BCG.

The primary antibody response in rabbits to a great variety of antigens is known to be heterogeneous, with the regular participation of at least two classes of immunoglobulin, a y-1 macroglobulin (IgM)' and a y-2 globulin with a sedimentation constant of 7 S (IgG) • (1-8). When studied with respect to sequence of appearance, IgM antibody has been found to be characteristic of the early primary response and IgG antibody has been associated with persistence of antibody synthesis. Recent studies using sensitive techniques have shown that IgG antibody may be present throughout the entire primary response (7, 8). The anamnestic response in rabbits is characterized by the rapid synthesis of large amounts of antibody that, under most experimental conditions, has been found to be of predominantly IgG type. Injection of minimal amounts of antigen has been shown to induce only the formation of IgM antibody during the primary response without preparing the animal for a subsequent anamnestic response (3, 5). A third class of immunoglobulin with a sedimentation constant of 9 S and {3 electrophoretic mobility has been recognized by