Separation and characterization of cortical and medullary bursal lymphocytes

Cortical and medullary lymphocytes from the chicken bursa of Fabricius were examined for their DNA content and [ 3 H]thymidine incorporation. The kinetics of the latter is different for both cell types, while chemical and cytophotometric tests showed cortical lymphocytes to contain more DNA. In addition, immunofluorescent detection of membrane‐bound immunoglobulins demonstrated that most medullary cells are B lymphocytes. Therefore, the cortex and the medulla appear to be distinct compartments of the bursal follicle, the cortex being a zone of continuous lymphocyte proliferation, while the medulla contains an homogeneous population with fully developed immunological competence.