Sample quality for the microarrays.

(A) Nalm-6 cells were cultured in serum-free medium on plates coated with Fn or PLL for various periods of time. Apoptosis was analyzed by flow cytometry using Annexin-propidium iodide staining after 1, 3 and 5 hours of culture on Fn (F) or PLL (P) or medium alone (C). P+ indicates culture on PLL in presence of serum. Cells were also lysed after for 15, 45 and 90 minutes of stimulation. Cell lysates were immunoprecipitated and analyzed by Western blot with anti–P-Tyr Ab. The results are representative of 3 experiments. (B) Comparison of gene expression changes induced by the technical variability (same sample on 2 chips) to 2 time point experiments (Fn vs PLL treatment, 8 and 48 hours). The data obtained with Affymetrix's GeneChip software (Avg Diff) were plotted. Twofold changes are indicated with straight lines.