III . X - LINKED B - LYMPHOCYTE DEFECT IN CBA / N MICE Abnormal Development of B - Lymphocyte

A substantial heterogeneity exists in the amount of immunoglobulin (Ig) on the surface of bone marrow-derived (B) lymphocytes as measured by labeling these cells with fluorescein-conjugated (F1) 1 anti-Ig and analyzing them by the technique of rapid flow microfluorometry (RFMF). Ig-bearing lymphocytes from neonatal mouse spleen and from adult mouse bone marrow are very diverse populations when studied in this way. However, fluorescence profiles of adult mouse spleen cells analyzed by RFMF display a distinct peak indicating the presence of a large subpopulation of cells with a low-to-intermediate density of surface Ig. By analysis of spleen cells from mice 1-4 wk of age, we have shown that this subpopulation of B lymphocytes develops with the maturation of the animal (1). In order to further define the functional significance of this population of Igbearing lymphocytes, we have studied the amount of Ig on the surface of individual lymphocytes from a strain of mice with an X-linked defect in Blymphocyte function. These mice, which are members of the CBA/N strain, fail to respond to certain thymus-independent antigens (2-4), display diminished responses to thymus-dependent antigens, and their lymphocytes have a markedly reduced potential to lyse antibody-coated EL-4 target cells (5). In addition, CBA/N mice have diminished numbers of Ig-bearing lymphocytes and these cells have an abnormally high ratio of surface IgM to putative IgD homolog (5, 6). In this communication, we report that adult lymphoid cells from the spleens of CBA/N mice labeled with F1 anti-Ig have a fluorescence profile which is characterized by a marked diminution in the population of B lymphocytes with a