IL-2 receptor α chain (CD25JAC) expression defines a crucial stage in pre-B cell development

The analysis of the expression of the a chain of the IL-2 receptor (CD25.TAC) on the surface of B lineage cells In mouse bone marrow reveals that it is a useful marker to distinguish pre-B-I from pre-B-II cells. CD25 Is not expressed on CD45R(B220)+ c-kit+ CD43+ TdT+ λ5+ Cμ− slg− lgH chain locus DJH-rearranged pre-B-I cells of mouse bone marrow. It is expressed on large cycling CD45R(B220)+ c-kit+ CD43+ TdT+ λ5+ Cμ− sig− and on small resting CD45R(B220)+ c-kit+ CD43− TdT+ λ5+ Cμ− sig− sig- IgH chain locus VHDJH-rearranged pre-B-II cells. Therefore, the transition from pre-B-I to large pre-B-II cells is marked by the downregulation of c-kit and terminal deoxynucleotldyl transferase (TdT), and by the upregulatton of CD25. SCID, RAG-2T, μMT and γ6T mutant mice do have normal, If not elevated numbers of pre-B-I cells but lack all CD25+ pre-B-II cells in their bone marrow. The expression of a transgenic H chain under control of the μH chain enhancer in RAG-2T bone marrow B lineage precursors allows the development of large and small CD25+ pre-B-II cells. The results suggest that the differentiation of pre-B-I to pre-B-II cells in mouse bone marrow requires the expression of μH chains and surrogate L chains in membranes, probably on the surface of precursor B cell