Selective effect of prodigiosin (PrG) 25-C and concanamycin B (CMB) on the function of mature cytotoxic T lymphocytes (CTLs). Mice (three per group) were immunized with P815 on day 0. On day 7, PrG 25-C (1 mg/kg, closed square) or CMB (0·4 mg/kg, closed triangle) was injected intraperitoneally (i.p.), or FK506 (300 mg/kg, open triangle; 600 mg/kg, open square) was administered orally. The CTL activity of pooled spleens (a), and anti-P815 antibody titre in the pooled serum (b) were determined on day 10. Immunized control, closed circle; naive control, open circle. The representative result of four experiments is shown.