IL-2 RECEPTOR-ALPHA CHAIN (CD25,TAC) EXPRESSION DEFINES A CRUCIAL STAGE IN PRE-B-CELL DEVELOPMENT

The analysis of the expression of the alpha 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(+) lambda(5)(+) c mu(-) slg(-) IgH chain locus DJ(H)-rearranged pre-B-I cells of mouse bone marrow. It is expressed on large cycling CD45R(B220)(+) c-kit(-) CD43(+) TdT(-) lambda(5)(+) c mu(+) slg(-) and on small resting CD45R(B220)(+) c-kit(-) CD43(-) TdT(-) lambda(5)(-) c mu(-) slg(-) IgH chain locus V(H)DJ(H)-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 deoxynucleotidyl transferase (TdT), and by the upregulation of CD25. SCID, RAG-2T, mu MT and lambda(5)T 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 pH chain enhancer in RAG-2T bone marrow a 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 mu H chains and surrogate L chains in membranes, probably on the surface of precursor B cells.