Circulating interleukin-6 levels are elevated in adult T-cell leukaemia/lymphoma patients and correlate with adverse clinical features and survival

We measured the circulating levels of interleukin (IL)-6 in adult T-cell leukaemia/lymphoma (ATL) patients using an enzyme-linked immunosorbent assay. The IL-6 levels in 59 ATL patients (median 8.2 pg/ml; range < 1.0 to 185.7 pg/ml) were significantly higher than in 30 healthy controls (median < 1.0 pg/ml; range < 1.0 to 3.5 pg/ml) (P < 0.0001) or 32 human T-lymphotropic virus type-I (HTLV-I) carriers (median 4.2 pg/ml; range  < 1.0 to 13.3 pg/ml) (P = 0.002). Among the ATL patients, the IL-6 levels in the acute- or lymphoma-type patients were significantly higher than those in the chronic-type patients (P < 0.0001). The IL-6 levels were also higher in the patients with B symptoms than in those without B symptoms (P = 0.039), and were significantly correlated with increased serum lactate dehydrogenase (LDH) (P = 0.0004) and C-reactive protein (CRP) (P < 0.0001) and decreased serum albumin (P = 0.0003) values. The patients with elevated IL-6 levels had inferior overall survival periods compared to those with normal IL-6 levels (P = 0.025). ATL is a single disease entity, although its clinical features are quite diverse; the increased production of cytokines may cause the diversity of clinical features. The results of our study indicate that IL-6 is one such cytokine.