Interleukin-6 and tumor necrosis factor in the pathogenesis of adverse reactions after treatment of lymphatic filariasis and onchocerciasis.

Adverse reactions following treatment of onchocerciasis and bancroftian filariasis are common and frequently severe. They are generally caused not by direct drug toxicity but by host inflammatory responses to dying microfilariae. To define the responsible mechanism, serial blood levels of interleukin-6 (IL-6) and tumor necrosis factor (TNF) were studied in 15 microfilaria-positive patients (10 with bancroftian filariasis, 5 with onchocerciasis) and 4 microfilaria-negative persons after diethylcarbamazine treatment. Elevations in IL-6 correlated with the occurrence and severity of clinical symptoms after treatment; for the onchocerciasis patients IL-6 levels directly reflected pretreatment intensity of infection. Serum TNF levels also rose but did not correlate directly with infection intensity or reaction severity. Microfilaria-negative controls remained asymptomatic with no significant rise in either cytokine. These findings suggest an etiologic role for systemically elevated cytokines in the inflammatory reactions developing after treatment of filarial infections in humans.