The possible presence of a bursa-independent, IgM-producing system in chicks.

The number of splenic plaque-forming cells significantly increased in bursectomized chicks immunized secondarily with SRBC. Further experiments using rabbit antiserum specific to the bursa of Fabricius indicate that the different types of antibody-producing cells might be engaged in the synthesis of IgM in bursectomized chicks. The possible presence of a bursa-independent, IgM-producing system in chicks is suggested.