IL-12 induces the expression of CD28 on a subpopulation of adherent LAK cells. The expression of CD28 is represented in function of CD4/CD8 expression for AKR-derived nylon wool purified spleen (A), IL-2 A-LAK (B), and IL-2/IL-12 A-LAK (C) cells as compared with SCID-derived nylon wool purified spleen (D), IL-2 A-LAK (E), and IL-2/IL-12 A-LAK (F) cells. The A-LAK cells were pretreated with 2.4G2 antibodies to block Fc receptors and subsequently incubated with phycoerythrin (PE)-labeled CD28 and fluorescein isothiocyanate (FITC)–labeled CD8 antibodies. The dot plots indicate the percentage of positive cells calculated via quadrant statistics using the suitable isotype controls.