Inhibition of cyclooxygenase-2 (Cox-2) attenuates the expression of transcription factors essential for plasma cell differentiation. RNA was isolated from freshly purified human peripheral blood B cells and cells stimulated with oligodeoxynucleotide (ODN) 2395 plus anti-immunoglobulin M (IgM) and treated with dimethylsulphoxide vehicle or the Cox-2 selective inhibitor SC-58125. Blimp-1, Xbp-1 and Pax5 messenger RNA (mRNA) steady-state levels were first normalized to 7S mRNA steady-state levels. (a) Blimp-1, Xbp-1 and Pax5 mRNA steady-state level fold change compared with freshly isolated B cells from one representative donor. Fold decrease of Blimp-1, Xbp-1 and Pax5 levels were determined by comparing vehicle-treated B cells with those treated with SC-58125. The mRNA fold decrease was averaged for four donors. (b) The mRNA fold decrease in the presence of 10 μm SC-58125 shown over a time–course of 24, 48, 72 and 96 hr; (c) mRNA fold decrease shown at 72 hr with 5, 10 or 20 μm doses of SC-58125; (d) ODN 2395 plus anti-IgM stimulated B-cell protein lysates (10 μg) collected at 72 hr from two separate donors were run using sodium dodecyl sulphate–polyacrylamide gel electrophoresis. The Western blot was probed for Blimp-1, Xbp-1, Pax5 and GAPDH control. (e) Densitometry results were normalized to GAPDH expression. Data are represented as mean ± SEM.