Bursal and thymic reticular epithelial cells in the chicken: induction of B- and T-lymphocyte differentiation by in vitro monolayer cultures.

The role of chicken bursal and thymic reticular epithelial cells (REp cells) in the induction of B- and T-lymphocyte differentiation has been investigated using in vitro culture of these cells. Splenic adherent cells were used as controls. Precursor populations were obtained predominantly from embryonic bone marrow or spleen and incubated with REp cell monolayers for 72 hr. Differentiation was assessed by the expression of specific membrane antigens: chicken B lymphocyte-specific antigen (CBLA) and chicken T lymphocyte-specific antigen (CTLA). Bursal REp cells specifically induced approximately 20-30% of the embryonic cells to express CBLA but had no influence on CTLA expression. Conversely, CTLA, but not CBLA, was induced in approximately 20% of the embryonic cells by the thymic REp cell cultures. No effect on the expression of either antigen was observed with the splenic adherent cells. The induced cells correspond to the first stage of B- and T-lymphocyte differentiation found in vivo. The assay system also facilitated the study of shifts in precursor content of various organs with development. Whereas embryonic bone marrow of all ages studied contained both B- and T-lymphocyte precursors, these were not demonstrable in donors after hatching. Use of 12-day embryonic bursa and thymus suspensions as sources of stem cells indicated that precommitment to the B- or T-lymphocyte lineage is irreversible.