Expression of IL-2 and IL-4 mRNA in tumor cell lines as detected by RT-PCR. Total RNA was extracted from various cell lines at 12, 24, 36, or 48 hours of ex vivo culture and was reverse-transcribed, and cDNA samples were subjected to PCR amplification using synthetic oligonucleotides primers for IL-2, IL-4, and β-actin as an internal control. The PCR product was electrophoresed through 1.5% agarose gel containing ethidium bromide. Lane 1, molecular size standard; lanes 2 through 5, cytokine gene expression at 12, 24, 36, and 48 hours of culture, respectively; lane 6, negative control consisting of normal unstimulated spleen cells from C57BL/6 mice; and lane 7, spleen cells cultured with ConA for 8 hours, used as a positive control.