Transitional B cells are observed in the bone marrow of wild-type and LTα^−/− mice. B-cell maturation in the bone marrow proceeds normally in the LTα-deficient mouse as revealed using antibodies to IgM, IgD, and CD21. Comparison of the expression of AA4.1, a marker of recent B-cell generation, revealed similar numbers of transitional cells in the bone marrow in wild-type and LTα null mice. A representative experiment is shown; n = 3 mice in each group. WT indicates wild type.