Interleukin-10 gene expression in adult T-cell leukemia

Abstract

We studied the serum levels of interleukin-10 (IL-10), in patients with adult T-cell leukemia (ATL) caused by human T-cell leukemia virus type I (HTLV- I) infection. Elevated IL-10 levels were observed in 33 of 45 patients with ATL. Fresh leukemic cells from ATL patients as well as HTLV-I-infected T-cell lines MT-2, SLB-1, and C10/MJ expressed IL-10 mRNA by reverse transcription- polymerase chain reaction analysis, whereas IL-10 mRNA was not detected in normal peripheral mononuclear cells and an uninfected T-cell line Jurkat. IL- 10 protein was also detected in the culture medium of leukemic cells from ATL patients as well as these HTLV-I-infected cell lines, and in the extracellular fluids of ATL patients. Interestingly, MT-4 cells, which did not express Tax although transformed by HTLV-I, did not express IL-10 at either the mRNA or protein level. To elucidate the role of the HTLV-I encoded transactivator Tax in IL-10 gene expression, Jurkat cells were transfected with a Tax expression plasmid. In transiently transfected Jurkat cells, endogenous IL-10 mRNA expression was induced by Tax. Stably transfected Jurkat cell lines expressed IL-10 mRNA and secreted IL-10 protein into the culture medium. The nuclear factor (NF)-κB pathway is a target for Tax transactivation. We treated MT-2 cells with phosphorothioate antisense oligonucleotides to the p65 subunit of NF-κB. A reduction in the expression of p65 was accompanied by a reduction in IL-10 gene expression and IL-10 production. We showed that the IL-10 κB-like sites (κB1, -2,034 to -2,025; κB2, -1,961 to -1,952; κB3, -452 to -443) specifically formed a complex with NF-κB-containing nuclear extract from MT- 2 cells and that NF-κB bound with the highest affinity to the κB2 element (κB2 > κB3 > κB1). These data suggest a general role for NF-κB activation in the induction of IL-10 gene transcription. Activation of IL-10 in HTLV-I- infected cells may contribute to the pathology associated with HTLV-I infection.