Unique expression of a small IL-32 protein in the Jurkat leukemic T cell line

Interleukin (IL)-32 was recently identified as a new cytokine which induces various proinflammatory cytokines in human monocytes and macrophages. Therefore, IL-32 has been primarily studied in inflammatory models such as rheumatoid arthritis and inflammatory bowel diseases. The regulation of endogenous IL-32 in other immune cells remains unknown. In the present study, we stimulated Jurkat T cells with phytohaemagglutinin (PHA) and phorbol myristate acetate (PMA) and examined IL-32 expression at both the mRNA and protein levels. All mRNAs of the four IL-32 isoforms and the 12-15 kDa IL-32 protein were independent of PHA and PMA stimulation, however a 9 kDa molecular weight IL-32 protein in the cell culture supernatant was induced by PHA and PMA after 16 h of stimulation. Compared to other human cell lines, the Jurkat cell line constitutively expressed a 12-15 kDa molecule of IL-32, which is smaller than the known IL-32 isoforms. We used IL-32 shRNA to examine the specificity of the 12-15 kDa molecule. Upon IL-32 shRNA transfection, the 12-15 kDa band was decreased specifically as compared to the control scrambled clone. Thus, the constitutive expression of IL-32 mRNA as well as the predominant production of a smaller sized IL-32 isoform in Jurkat cells may implicate a role for IL-32 in human T cell leukemia.