B-CELL EMIGRATION DIRECTLY FROM THE CORTEX OF LYMPHOID FOLLICLES IN THE BURSA OF FABRICIUS

In the peripheral blood (PBL) of juvenile chickens three populations o f B cells have previously been distinguished based on life-span and or igin of cells within each population. In this report we show that the largest PBL B cell subset, population 1 B cells, which are short-lived cells corresponding to about 60 % of PBL B cells and the vast majorit y of bursal emigrants, exit from the bursa directly from the follicula r cortex. This conclusion is based on the specific labeling of rapidly dividing cortical lymphocytes with bromodeoxpuridine, followed by the ir detection in the periphery prior to the appearance of bromodeoxyuri dine labeled cells in the bursa medulla. Furthermore, the rate of emig ration of cortical lymphocytes, 1.00 +/- 0.1 % of PBL B cells per hour , is indistinguishable from the emigration rate of B cells from the bu rsa as a whole. The anatomical organization of the bursa has evolved t o focus gut-derived antigens from the bursal lumen into the lymphoid f ollicles. The emigration of cortical bursal cells is discussed in rela tion to the exposure of bursal lymphocytes to extrinsic antigen.