B cell production in adult rats

Splenic T zone development is B cell dependent

The factors regulating growth and patterning of the spleen are poorly defined. We demonstrate here that spleens from B cell-deficient mice have 10-fold reduced expression of the T zone chemokine, CCL21, a threefold reduction in T cell and dendritic cell (DC) numbers, and reduced expression of the T zone stromal marker, gp38. Using cell transfer and receptor blocking approaches, we provide evidence that B cells play a critical role in the early postnatal development of the splenic T zone. This process involves B cell expression of lymphotoxin (LT)alpha1beta2, a cytokine that is required for expression of CCL21 and gp38. Introduction of a B cell specific LTalpha transgene on to the LTalpha-deficient background restored splenic CCL21 and gp38 expression, DC numbers, and T zone size. This work also demonstrates that the role of B cells in T zone development is distinct from the effect of B cells on splenic T cell numbers, which does not require LTalpha1beta2. Therefore, B cells influence spleen T zone development by providing: (a) signals that promote T cell accumulation, and: (b) signals, including LTalpha1beta2, that promote stromal cell development and DC accumulation. Defects in these parameters may contribute to the immune defects associated with B cell deficiency in mice and humans.

A phenotypic study of B lymphocyte subpopulations in human bone marrow

The regulatory mechanisms that monitor the size of the peripheral B cell pool and determine cell death or survival are poorly understood. In rodents B lymphopoiesis is maintained at a high rate throughout adult life, and under resting conditions there is little recruitment into the long-lived peripheral pool; it therefore follows that most newly formed B lymphocytes have a very short lifespan. The maturation stages of B lymphopoiesis in humans and in experimental mammals appear to be similar. We have determined the phenotype of sIgM- and sIgD-expressing cells from normal adult human bone-marrow and peripheral blood by dual immunofluorescence with an extensive panel of monoclonal antibodies representative of major B cell clusters, in order to identify antigenic differences that may play a regulatory role. Antibodies of the CD21, CD22 and CD9 clusters, the unclustered restricted B antibody 7-F-7 and anti-IgD were reactive with different proportions of sIgM+ cells in blood and bone marrow; 29.5% (range 5-60%) of sIgM+ cells in marrow were sIgD- and most of these cells were also CD21- and CD22-, thus defining a unique marrow population. However, newly formed and mature re-circulating cells comprising the sIgM+sIgD+ population could not be distinguished by the panel of antibodies.

Development of B lymphocytes in mice heterozygous for the X-linked immunodeficiency (xid) mutation. xid inhibits development of all splenic and lymph node B cells at a stage subsequent to their initial formation in bone marrow

CBA/N mice were crossed with CBA/Ca-Pgk-1a to produce female F1 hybrids that were heterozygous for both xid and the phosphoglycerate kinase 1 (PGK-1) allozymes. PGK acted as a quantifiable marker for the frequency of cells in which the xid-bearing X chromosome was active in lymphocytic and other cell populations. In adults, such cells (termed xid cells) were virtually absent in FACS-sorted splenic and lymph node B cells, and in all three splenic subpopulations distinguished on the basis of their relative expression of membrane mu and delta chains. Thus, the xid mutation appeared to compromise the development of all B cells. Erythrocytes, thymocytes, T cells, and granulocytes were unaffected. Selection against xid cells was less pronounced in the spleens of 2-6-wk-old mice. In the bone marrow, there was evidence for selection against xid in the production of B cells (except at 2 wk of age), but not at the pre-B cell level. These data suggest that, in competition with normal non-xid cells, newly-formed xid B cells were less likely to be incorporated into the peripheral B cell pool.