Fetal liver organ cultures allow the proliferative expansion of pre-B receptor-expressing pre-B-II cells and the differentiation of immature and mature B cells in vitro

We describe the phenotypic and functional properties of a lineage cells developing in fetal liver organ cultures (FLOC) of mouse embryos at day 14 or 15 of gestation which contain pro/pre-B-I cells. FLOC a cell development proceeds to mature IgM⁺, IgD⁺ and CD23⁺ lipopolysaccharide-reactive a cells within a culture period of 5-6 days. The phenotypes and relative proportions of pro/pre-B-I, pre-B-II, immature and mature a cells from FLOC were similar to that seen in livers freshly isolated from age-matched, i.e. newborn, mice. More importantly, the numbers of cells recovered in the different a lineage subpopulations from FLOC were close to those developed in vivo. Hence, in contrast to single-cell suspension cultures of fetal liver, FLOC allow the proliferative expansion of pre-B cell receptor-expressing pre-B-II cells. FLOC from embryos of mice with targeted mutations in the RAG-2 and λ₅ genes, which cannot expand by proliferative expansion of their pre-B-II compartment in vivo because they cannot express a pre-B cell receptor on their surface, show this same defect in vitro. FLOC are accessible to the action of mAb and cytokines. Thus, addition of anti-IL-7 receptor mAb to FLOC of normal mice inhibits a cell development at the transition of pro/pre-B-I to pre-B-II cells. This inhibition is reversed by addition of excess rIL-7. Addition of IL-7 alone stimulates the proliferation of pro/pre-B-I cells and inhibits their differentiation to pre-B-II and immature a cells, as it does in single-cell suspension cultures. FLOC should be useful to study the effects of other mAb, cytokines, ligands and other molecules on early a cell development.