Antagonist anti-CD70 antibody blocks the induction of B-cell proliferation and Ig secretion by pDCs. pDC/B-cell coculture was established, and antagonist anti-CD70 antibody or purified mouse IgG₁ isotype control at a concentration of 10 μg/mL was added to the wells as indicated. Antibody and pDCs were added and incubated at 37°C for 30 minutes before the addition of B cells. (A) Proliferation was assessed by measuring [³H]-thymidine incorporation on day 3. Results shown indicate the average of triplicate results from 1 donor representative of 5. (B) Supernatant was collected on day 14, and IgG and IgM levels were determined by ELISA. Each point represents the average of duplicate results for 1 individual donor. Data were analyzed by unpaired t test: *P < .05.