B-cell differentiation in the chicken: expression of immunoglobulin genes in the bursal and peripheral lymphocytes.

We have studied the expression of immunoglobulin genes in the chicken B-cell precursors, and of a B-cell surface marker (Bu-1) on the bursal and peripheral B cells during normal ontogeny. Since there is no way of distinguishing the precursor cells from the more mature bursal lymphocytes on the basis of surface markers, we chose to study the total bursal lymphocyte population at ages when the numbers of the various precursor cells (bursal, early post-bursal, and post-bursal stem cells) in the bursa are estimated to be at their highest. Thereafter, comparisons with the more mature lymphocytes in the peripheral organs were made. As a result, levels of the lambda and mu transcripts and expression of Bu-1 antigen in the chicken B-cell precursors were found to be unchanged during the post-hatching period. In the light of these experiments, the later events of B-cell differentiation, i.e. the development from the bursal to post-bursal B lymphocytes, occurs without the lambda, mu, and Bu-1 gene loci involved. On the other hand, the higher level of lambda and mu expression in the splenic B lymphocytes indicates that the post-bursal stem cells mature into highly active plasma cells after seeding to the peripheral organs.