Output of B cells in LPC cultures is reduced in HOXA9−/− mice. Output of B cells from 5-week LPC cultures was determined. Total B cells, B220⁺ cells; pro-B cells, B220⁺CD43⁺ cells; pre-B cells, B220⁺CD43⁻ cells. Counts are expressed as the mean number of cells harvested at week 5 per 10⁶ marrow cells originally plated. Marrow samples from four animals were studied in each group. (□) A9−/−; () A9+/−; (▪) C57; (▧) 129. *P < .05 for A9−/− versus C57 and 129; not significant for A9−/− versus A9+/−.