Interleukin 6 during active visceral leishmaniasis and after treatment.

To determine the utility of the serum concentrations of interleukin 6 (IL-6) as a marker of disease activity and therapeutic efficacy in visceral leishmaniasis (VL), IL-6 levels were measured in 19 patients with active VL from Sudan before and after treatment. IL-6 levels were 30 +/- 6 pg/ml during the active phase of the disease, decreased to levels around the detection limit of the assay (2 pg/ml) directly after successful antimony therapy, and remained low or undetectable for up to 6 months in persistently cured patients (P < 0.005 versus baseline). In 2 patients who had a relapse of VL, IL-6 was elevated at the time the relapse was diagnosed. Two patients with post-kala-azar dermal leishmaniasis did not have detectable IL-6 in their circulation. Sequential measurements of serum IL-6 levels may be useful for monitoring therapeutic efficacy in patients with VL.