Production of T helper 1 (Th1) and T helper 2 (Th2) cytokines by spleen cells from control and orally immunized mice. Spleen cells from control BALB/c mice, or BALB/c mice 1 or 7 days after the last oral immunization with B10 spleen cells, were stimulated in vitro with irradiated B10 cells and the production of interleukin (IL)-2, IL-4, IL-10 and interferon-γ (IFN-γ) was determined by enzyme-linked immunosorbent assay (ELISA). Each bar represents the mean value (± SD) from six individual mice. Values with asterisks differ significantly (*P < 0·05, **P < 0·01) from the value for control mice.