Development of B lymphocytes in the mouse; studies of the frequency and distribution of surface IgM and IgD in normal and immune-defective CBA/N F1 mice.

Affinity-purified anti-mouse mu and delta antibodies and flow microfluorometric techniques were utilized to study the frequency and distribution of sIgM and sIgD on adult and neonatal B lymphocytes of immunologically normal mice and mice with the immune-defect characteristic of the CBA/N strain. Neonatal normal B lymphocytes can be distinguished from their adult counterparts by the presence of increased amounts of sIgM on sIgM+ cells and by the increased number of sIgM+IgD- cells. The most primitive B lymphocytes of immunologically normal mice appear to reside in the bone marrow of 1- to 2-wk-old mice and are distinguished from splenic B lymphocytes at this time by their relatively low amounts of sIgM. However, in the adult, splenic and bone marrow B lymphocytes are indistinguishable with regard to the quantities of their sIgM or sIgD. Adult immune-defective mice have increased amounts of sIgM on their B lymphocytes, although the number of sIgM+ IgD- cells in these mice is not increased. During development, however, larger than normal numbers of sIgM+ IgD- cells are found in the spleen and bone marrow of these mice; and the low frequency of such cells seen in normal adults is not achieved in immune defectives until after the 56th day of life. Thereafter, immune-defective mice have low frequencies of B lymphocytes with high relative amounts of sIgM, even after 1 yr or age.