Effect of IL-12 on IL-12 and Th2-like cytokine expression by primary B cells. Purified primary B cells were treated for 48 hours with IL-12 or with IL-12 plus IL-18. The corresponding cDNA was amplified with IL-12 p40, IL-12 p35, IL-4, IL-5, and IL-13. The results of PCR product migration are shown in panels A and B. As controls, we used the RPMI 8866 B-cell line for IL-12 p40 expression and purified T cells activated with anti-CD3 for Th2-like cytokines.