We have reported previously that the response of IFN-) I mRNA expression to the stimulation of concanavalin A (ConA) in peripheral blood mononuclear cells (PBMC) in patients who had extensive chronic graft-versus-host disease (cGVHD) after allogeneic bone marrow transplantation (allo BMT) was not increased compared with those without extensive cGVHD. A similar low response of IL-2 and IL-5 mRNA expression to ConA was observed in such patients with extensive cGVHD (1). Based on these findings, we have investigated the response of IL-4, IL-10 and IL-13 (Th2 cytokines) as well as IL-12 (Th2-suppressing cytokine) mRNA expression in PBMC to the stimulation of ConA in patients receiving allo-BMT, since IFN-) I and IL-2 are produced mainly by Thl cells and IL-5 is produced mainly by Th2 cells. Three patients with extensive cGVHD, 5 patients with limited cGVHD, 4 patients without cGVHD, 2 patients in acute phase (3 months after allo-BMT), 1 patient each after auto-and syngeneic BMT and 2 normal individuals were analysed in the present study. PBMC were obtained from heparinized fresh blood samples and cultured at 106/ml in RPMI-1640 medium containing 10% fetal calf serum and 5 x M 2-mercaptoethanol. Replicate cultures then received either no stimulation or stimulation by addition of Con A (Pharmacia Fine Chemicals, Uppsala, Sweden) at a final concentration of 5 pg/ml for 12 h. The cells were harvested and the total RNA was extracted and then cytokine gene expression was analysed by semiquantitative RT-PCR as reported previously (Table 1)(1-5). Each 5 pg of total RNA was reverse-transcribed with 600 U of murine Moloney leukemia virus reverse transcriptase (BRL, Grand Island, NY, USA) and 150 pmol of random hexamer. An aliquot (1/20th) of the resulting cDNA was used for the semiquantitative polymerase chain reaction (PCR). The following primers were synthesized using a 380B DNA synthesizer (Applied Biosystems):