FETAL LIVER ORGAN-CULTURES ALLOW THE PROLIFERATIVE EXPANSION OF PRE-BRECEPTOR-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 cell s 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(+) lipopolysac charide-reactive a cells within a culture period of 5-6 days, The phen otypes and relative proportions of pro/pre-B-I, pre-B-II, immature and mature B cells from FLOC were similar to that seen in livers freshly isolated from age-matched, i.e. newborn, mice, More importantly, the n umbers of cells recovered in the different B lineage subpopulations fr om FLOC were close to those developed in vivo, Hence, in contrast to s ingle-cell suspension cultures of fetal liver, FLOC allow the prolifer ative expansion of pre-a cell receptor-expressing pre-B-II cells, FLOC from embryos of mice with targeted mutations in the RAG-2 and lambda( 5) genes, which cannot expand by proliferative expansion of their pre- B-II compartment in vivo because they cannot express a pre-B cell rece ptor on their surface, show this same defect in vitro. FLOC are access ible to the action of mAb and cytokines, Thus, addition of anti-IL-7 r eceptor 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 revers ed 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, cy tokines, ligands and other molecules on early a cell development.