The pathogenesis of filarial disease is characterized by acute and chronic inflammation. Inflammatory responses are thought to be generated by either the parasite, the immune response, or opportunistic infection. We show that soluble extracts of the human filarial parasite Brugia malayi can induce potent inflammatory responses, including tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and nitric oxide (NO) from macrophages. The active component is heat stable, reacts positively in the Limulus amebocyte lysate assay, and can be inhibited by polymyxin B. TNF-α, IL-1β, and NO responses were not induced in macrophages from lipopolysaccharide (LPS)-nonresponsive C3H/HeJ mice. The production of TNF-α after chemotherapy of microfilariae was also only detected in LPS-responsive C3H/HeN mice, suggesting that signaling through the Toll-like receptor 4 (TLR4) is necessary for these responses. We also show that CD14 is required for optimal TNF-α responses at low concentrations. Together, these results suggest that extracts of B. malayi contain bacterial LPS. Extracts from the rodent filaria, Acanthocheilonema viteae, which is not infected with the endosymbiotic Wolbachia bacteria found in the majority of filarial parasites, failed to induce any inflammatory responses from macrophages, suggesting that the source of bacterial LPS in extracts of B. malayi is the Wolbachia endosymbiont. Wolbachia extracts derived from a mosquito cell line induced similar LPS-dependent TNF-α and NO responses from C3H/HeN macrophages, which were eliminated after tetracycline treatment of the bacteria. Thus, Wolbachia LPS may be one of the major mediators of inflammatory pathogenesis in filarial nematode disease.

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