ATRA and 9-cis-RA upregulate the expression of IL-4 and IL-5 mRNA and down-regulates the expression of IFN-(within anti-CD3 mAb-stimulated PBMC. Taqman® semi-quantitative PCR for IL-4, IL-5 and IFN-(transcripts was performed using total cellular RNA of 48 h, anti-CD3 mAb-activated PBMC (2.5 × 106/ml) treated with ETOH or 10-7 M of ATRA (□) or 9-cis- RA (■). The media used in this experimental series also contained a low dose of rhIL-2 (10 U/ml). Values obtained for each cytokine message was normalized to that obtained for 18S rRNA in the same sample as described in the Methods. The normalized values were then expressed as a function of the ETOH control sample. The relative copy number of PBMC IL-4 and IL-5 was increased by ATRA and 9-cis-RA in all donors tested, while the relative copy number of IFN-(mRNA were decreased by ATRA. The results are expressed as relative fold increase or decrease in mRNA expression. A paired T test was performed on the values derived from five donors as described in the Methods and the P values from the pooled donor data comparisons are listed for each cytokine and RA stimulation.