Induction of IgG, IgM, and IgA immunoglobulin production is decreased in preterm cord blood–derived B cells in response to CD40L plus IL-10 compared with adult blood B cells. Naive B cells were stimulated with the indicated ligands or medium alone for 10 days, and IgG (A), IgM (B), and IgA (C) production from the culture supernatants were measured by ELISA. Data are shown as mean (± SEM) of 10 independent experiments using 10 independent adult (AB), cord (CB), or preterm cord (PreCB) blood samples with each assay performed in triplicate. Statistically significant differences are shown. *P < .001; **P ≤ .005.