B cells precursors in the lung express markers of resistance to apoptosis and proliferation.

<p>(a) The apoptosis regulator Bax is downregulated in pre/early pro-B cells (B220⁺CD43⁺BP-1^-) upon allergen exposure. (b) Newly produced total B (B220+SSClow), pre/early pro-B and pre-B cells (B220⁺CD43^-BP^-1⁺) increase in the lung upon allergen exposure, as designated by increased expression of the thymidine analogue BrdU (5-bromo-29-deoxyuridine). (c) Pre/early pro-B cells and pre-B cells proliferate <i>in-situ</i> during allergen exposure. Data are presented as mean ± SEM, % refers to the percentage of positive cells out of total cells of each population, n = 5–8 mice/group, * <i>p</i> < 0.05.