Inflammatory Responses Induced by the Filarial Nematode Brugia malayi Are Mediated by Lipopolysaccharide-like Activity from Endosymbiotic Wolbachia Bacteria

Abstract

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.

Innate Immune Responses to Endosymbiotic Wolbachia Bacteria in Brugia malayi and Onchocerca volvulus Are Dependent on TLR2, TLR6, MyD88, and Mal, but Not TLR4, TRIF, or TRAM

“…Our earlier observations using in vitro and in vivo models suggested that innate immune responses to Wolbachia contained in the filarial nematodes B. malayi and O. volvulus induced inflammation via TLR4 because C3H/HeJ mice expressing a nonfunctional TLR4 due to a point mutation in tlr4 (46) showed decreased responses relative to C3H/HeN mice with the functional wild-type TLR4 (25,28). These earlier observations did not unequivocally exclude endotoxin contamination as a potential TLR4 receptosome ligand.…”

“…Previous studies showed that the presence of Wolbachia was essential for filarial-induced macrophage activation (25). To determine whether TLR2 is also important in the induction of inflammatory responses by immunocompetent C57BL/6 macrophages, we used a neutralizing Ab directed against the epitope binding C terminus region of TLR2.…”

“…Aside from these drug-related side effects, the contribution of Wolbachia to inflammation in infected individuals is unresolved, but several observations suggest they may also play a role in initiating or perpetuating local or systemic inflammatory reactions. First, filarial-induced innate immune cellular activation is ablated if the parasites or infected animal hosts are pretreated with tetracycline antibiotics that partially eliminate intracellular Wolbachia (10,25,26). Second, Wolbachia isolated from filaria or from insect cell lines elicit inflammatory responses similar to those of filarial extracts containing Wolbachia (26,27).…”

Mapping the presence of Wolbachia pipientis on the phylogeny of filarial nematodes: evidence for symbiont loss during evolution

“…In this way, L. yutajensis could become a valid alternative to the use of A. viteae (which is negative for W. pipientis) as a sort of 'negative control' (e.g. see Hoerauf et al, 1999;McCall et al, 1999;Taylor et al, 2000 andSaint André et al, 2002), being more closely related to a filarial model which harbors W. pipientis (L. sigmodontis) than A. viteae (see Casiraghi et al, 2001b). Litomosoides species are thought to have evolved as parasites of bats in South America, and diversified in rodents only recently (about 3 millions years), when these migrated from North America during the Pliocene-Pleistocene; their passage into small marsupials is also believed to have occurred after the Pliocene-Pleistocene Philipp, 1991 andGuerrero et al, 2002).…”

Antagonism of microRNA-126 suppresses the effector function of T H 2 cells and the development of allergic airways disease

“…Lipopolysaccharide (LPS), a cell wall component of Gram-negative bacterial, activates cells through TLR4 and the common TLR adaptor protein myeloiddifferentiation-primary-response-gene-88 (MyD88) resulting in activation of transcription and proinflammatory pathways (7,9,10). LPS is also a prominent constituent of asthma-inducing house dust mite (HDM) allergens and can instruct the immune response to inhaled antigen to generate T H 2 responses (5).…”