Post-irradiation regeneration of early B-lymphocyte precursor cells in mouse bone marrow

To examine the sequential development of early B-cell precursors in mouse bone marrow, B-lineage cells have been examined during a wave of post-irradiation regeneration. Cell phenotypes have been defined using double-immunofluorescence labelling techniques for (i) terminal deoxynucleotidyl transferase (TdT); (ii) B220 glycoprotein, detected by the binding of mAb 14.8; (iii); mu heavy chains in the cytoplasm (c mu) and at the cell surface (s mu). Three populations of mu- cells (TdT+14.8-; TdT+14.8+; TdT-14.8+) have been proposed to be early B-cell precursors which would give rise to c mu+s mu- pre-B cells and thus to s mu+ B lymphocytes. From 3 to 7 days after a sublethal dose (150 rads) of whole body gamma-irradiation, the B-lineage cells recovered rapidly to exceed normal numbers. The early B-cell precursors increased to peaks of 1.8-2.5 times normal numbers, preceding by 1 day a comparable increase and overshoot of c mu+s mu- pre-B cells, followed by recovery of s mu+ B lymphocytes. The TdT+14.8- cells peaked first at 5 days, subsiding again at 7-10 days with a shift from large- to medium-sized cells. The TdT+14.8+ cells showed a later peak (6 days), a more sustained wave in cell numbers and a delayed shift in cell size. The substantial population of 14.8+ mu- cells reached maximal observed values at 7 days and still maintained a predominantly large cell size profile at 10 days. The timing, cell-size shifts and progressive amplification of the waves of regeneration accord with a dynamic model in which the TdT+14.8-,TdT+14.8+ and TdT-14.8+ cells form three successive stages in B-cell differentiation before the expression of mu chains, presumptively including the stage of mu chain gene rearrangement. In addition, the results provide an experimental system for the enrichment of early B-cell precursors in mouse bone marrow.