In interleukin-7-transgenic mice, increasing B lymphopoiesis increases follicular but not marginal zone B cell numbers

Follicular and marginal zone B cells constitute the vast majority of mature B cells in the adult spleen. The inter-relationships between these two functionally and phenotypically distinct subpopulations of B cells remain unclear. In situations of decreased bone marrow B lymphopoiesis, the proportion of spleen marginal zone B cells increases, but the consequence of increasing B lymphopoiesis on marginal zone B cells has not been investigated. Using interleukin-7-transgenic mice, in which B lymphopoiesis is significantly increased, we show that the number of follicular B cells increased about fivefold but the number of marginal zone B cells decreased. Functional and phenotypic analysis, including in vivo bromodeoxyuridine labeling experiments, showed that marginal zone B cells in transgenic mice were indistinguishable from controls. Mixed radiation bone marrow chimeras showed that marginal zone B cells developed equally well from both normal and transgenic adult bone marrow B cell progenitors. Taken together, these results suggest that interleukin-7 does not influence the lineage choice between follicular and marginal zone B cells and that the number of cells in each compartment is independently regulated.