Interaction with monocytes enhances IL-5 gene transcription in peripheral T cells of asthmatic patients

The regulatory mechanisms of IL-5 gene transcription in human peripheral T cells are unclear because the transfection efficiency of plasmid constructs into nontransformed T cells is very low.

Concanavalin A (ConA)-stimulated blastocytes derived from peripheral blood lymphocytes of asthmatic subjects were transiently transfected with the human IL-5 gene promoter/enhancer-luciferase gene construct, pIL-5 (-511)Luc, and cultured with THP-1 cells (human monocytoid cells) and anti-CD3 monoclonal antibody (mAb). IL-5 level in the culture medium was determined by an enzyme-linked immunosorbent assay. Transcriptional activity of the IL-5 gene was measured by luciferase reporter analysis.

ConA-blast lymphocytes of asthmatic patients produced a significant amount of IL-5 upon combined stimulation with anti-CD3 mAb and THP-1 cells, but not with anti-CD3 mAb alone. Costimulation with anti-CD28 mAb also enhanced the anti-CD3 mAb- induced IL-5 production. Accordingly, luciferase activity induced by anti-CD3 mAb stimulation in pIL-5(-511)Luc-transfected ConA-blast lymphocytes was increased 1.9- and 3.4-fold by the addition of anti-CD28 mAb and THP-1 cells, respectively. Serial 5' deletion analysis of the reporter gene demonstrated that the cis-regulatory element located at -119 to -80 is critical for anti-CD3 mAb-induced IL-5 gene transcription.

Our present findings provide a useful model reflecting IL-5 gene transcription in human peripheral T cells in vivo, and clearly demonstrate that an interaction with monocytes enhances IL-5 gene transcription.