rIL-24 inhibits plasma cell maturation. (A) GC B cells from tonsils were stained and CD20^hiCD38^hi cell sorted and cultured for 3 days with IL-2, IL-10, and soluble CD40L. A secondary culture was performed with IL-2 + IL-10 with or without IL-24 for 4 additional days and cells analyzed at day 7 by immunostaining using anti-CD38 and anti-CD20 MAbs. CD38⁺ cells were also analyzed based on their size (CD38 vs FSC) showing CD38^hiFSC^hi, CD38⁺FSC⁺, and CD38⁺FSC^lo R1 to R3 population, respectively. (Right) For each condition, cells were stained with propidium iodide for cell-cycle analysis. Percentages on histograms from left to right show the respective amounts of hypodiploid cells, and cells in G0/G1 and S+G2/M phases of the cell cycle. (B) The respective percentages of CD20⁻CD38⁺ and CD20⁺CD38⁻ in secondary culture at day 7 with or without IL-24 were calculated (n = 6). (C) Secondary culture with IL-24 inhibits IgG production. GC B cells were cultured as above in IL-2 + IL-10 + CD40-L for 3 days and thereafter in IL-2 + IL-10 with or in the absence of IL-24. Supernatants from cells were collected at days 7 and 10 and the concentration of IgG was measured by ELISA (n = 5). (D) Cells cultured with or without the addition of IL-24 in the secondary culture were restimulated at day 7 or day 11 with IL-2 + IL-10 + CD40-L for 3 more days and tritiated thymidine (0.5 μCi [0.0185 MBq]/well per 100 000 cells) was incorporated overnight after 3 days (days 10 and 14).