Infliximab enhances plasma cell differentiation. (a) Circulating plasma cell levels in rheumatoid arthritis (RA) patients treated by infliximab with anti-nuclear antibody (ANA) (n = 10) or without ANA production (n = 10), in patients with active systemic lupus erythematosus (SLE) (n = 10), and in healthy volunteers (n = 10). Plasma cell levels were measured in peripheral blood. The mean number/milliliter of CD38+CD19+CD20- is shown (mean ± standard deviation). *P < 0.001, Mann–Whitney U test. (b) Peripheral blood mononuclear cells (PBMCs) from healthy donors were cultured out in the presence of influenza virus (Flu) with or without infliximab or TNFα. After 10 days, we analyzed by flow cytometry the proportion of CD19+CD20-CD38high+ plasma cells. Data expressed as the mean ± standard error of the mean of three independent experiments. (c) PBMCs from healthy donors, from RA patients treated by infliximab and developing ANAs, and from SLE patients were cultured in the presence of influenza virus with or without the TNFα blocker, infliximab. After 15 days, ANA titers were measured in the supernatants. Data expressed as mean ± standard error of the mean of three independent experiments.