Expression of BAFF and APRIL mRNAs and proteins in normal blood and tonsil B lymphocytes and in B-CLL cells. (A) Total RNA was extracted from purified B lymphocytes from the blood of healthy volunteers or of patients with B-CLL or from tonsils. After RT, cDNAs were subjected to PCR amplification with specific primers for BAFF (lane a, 337 bp), APRIL (lane b, 365 bp), and β₂-microglobulin as control (lane c, 169 bp). *Similar results were obtained after further purification of the leukemic B cells by CD19⁺ selection. U937 and EHEB cell lines were used as controls of expression. Negative controls were used in the absence of cDNA and of Taq. (B) Total lysates from purified B lymphocytes from the blood of healthy volunteers or B-CLL patients or from tonsils were analyzed by Western blotting and were revealed either with a rabbit anti-BAFF polyclonal antibody (lane b), with a goat anti-APRIL polyclonal antibody (lane d), or with a mouse antiactin monoclonal antibody as a control of roughly equal deposit of proteins (lanes a and c). *Similar results were obtained after further purification of the leukemic B cells by CD19⁺ selection. Lysates of U937 and RAJI cell lines were used as positive controls for BAFF and APRIL expression, respectively.