Injection of human thyroglobulin solution into rabbits gave rise to a transient 19S antibody response which could however be maintained by repeated administration of antigen. When the antigen was coated onto acrylic resin particles, the titre of 19S antibodies was increased nearly 20-fold whereas 7S antibody levels were unchanged. This selective enhancement of 19S antibody synthesis by particulate antigen was also seen using human γ-globulin. "Intermediate" sedimenting and 7S γ1-antibodies were also increased in animals given particulate antigen. These phenomena may be due to prolonged persistence of the antigen in appropriate macrophages or perhaps to an increased uptake into these cells. The results are discussed in terms of the relationship between 19S and 7S globulin-producing cells.

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