Figure 4.

Effect of de novo synthesis of transgenic μH-chain on proliferation of in vitro cultured B cell precursors. CD19⁺ pro-B cells were isolated from various dTg mice that had received tetracycline (200 μg/ml) in the drinking water for at least 7 days and cultured as indicated in the absence (open symbols) and presence (filled symbols) of tetracycline. Cell numbers were determined by flow cytometry. (A) Pro-B cells from dTg rag-2^−/− mice were plated on ST-2 stromal cells and cultivated in the presence (●) or absence (○) of tetracycline. Mean values and standard errors were calculated from triplicates. In five independent experiments an 8- to 14-fold increase in cell numbers was observed 5 days after initiating the cultures in the absence of tetracycline. (B) Forward light scatter characteristics of B cell precursors from dTg rag-2^−/− mice cultured on stromal cells in the presence (+ tet) or absence (− tet) of tetracycline. Percentages of large cells are indicated. (C) CD19⁺ pro-B cells from dTg rag-2^−/−/λ5^−/− mice were plated on ST-2 stromal cells and cultured in the presence (●) or absence (○) of tetracycline over a period of 3 days. (D) CD19⁺ pro-B cells from dTg rag-2^−/− mice were plated on stromal cells and cultivated with (filled symbols) or without (open symbols) tetracycline in the presence of blocking antibodies specific for c-kit (rectangles, 20 μg/ml) or the IL-7Rα-chain (triangles, 20 μg/ml).