Toll-Like Receptor 2 Regulates CXC Chemokine Production and Neutrophil Recruitment to the Cornea inOnchocerca volvulus/Wolbachia-Induced Keratitis

Abstract

The filarial nematode Onchocerca volvulus is the causative organism of river blindness. Our previous studies demonstrated an essential role for endosymbiotic Wolbachia bacteria in corneal disease, which is characterized by neutrophil infiltration into the corneal stroma and the development of corneal haze. To determine the role of Toll-like receptors (TLRs) in neutrophil recruitment and activation, we injected a soluble extract of O. volvulus containing Wolbachia bacteria into the corneal stromata of C57BL/6, TLR2 ؊/؊ , TLR4 ؊/؊ , TLR2/4 ؊/؊ , and TLR9؊/؊ mice. We found an essential role for TLR2, but not TLR4 or TLR9, in neutrophil recruitment to the cornea and development of corneal haze. Furthermore, chimeric mouse bone marrow studies showed that resident bone marrow-derived cells in the cornea can initiate this response. TLR2 expression was also essential for CXC chemokine production by resident cells in the cornea, including corneal fibroblasts, and for neutrophil activation. Taken together, these findings indicate that Wolbachia activates TLR2 on resident bone marrowderived cells in the corneal stroma to produce CXC chemokines, leading to neutrophil recruitment to the corneal stroma, and that TLR2 mediates O. volvulus/Wolbachia-induced neutrophil activation and development of corneal haze.Onchocerca volvulus is endemic in at least 27 sub-Saharan African countries and in Yemen (3). A recent study concluded that the incidence of onchocerciasis has been underreported, and rapid epidemiological mapping indicated that an estimated 37 million individuals are infected with this parasite and another 90 million are at risk (3). Adult males and females are present in collagenous nodules in subcutaneous tissues and release millions of first-stage larvae (microfilariae) into the skin over their 10-to 15-year life span. Microfilariae migrate throughout the skin and can penetrate ocular tissues, including the cornea, resulting in chronic sclerosing keratitis. Studies of posttreatment reactions in infected individuals indicate that most clinical manifestations occur in response to degenerating microfilariae and the release of endosymbiotic Wolbachia bacteria, as indicated by elevated Wolbachia DNA and elevated proinflammatory cytokines in the blood (12,28,42). Wolbachia spp. belong to the family Rickettsiaceae and, in addition to infecting insects and other arthropods, are present in the hypodermis of all larval and adult filarial stages and in the uterus of adult female worms (33, 40). Since neutrophils are abundant in untreated nodules containing Wolbachia but not in nodules from antibiotic-treated individuals (7), it is likely that Wolbachia bacteria are important in recruiting neutrophils to the tissues. Neutrophils are also evident around microfilariae in the skin of chronically infected individuals (18,25).Wolbachia bacteria appear to be responsible for the early stages of corneal inflammation in a murine model of river blindness, as intrastromal injection of isolated Wolbachia or filarial extracts containing Wolba...

Differential induction of Th2- And Th1-associated responses by filarial antigens and endosymbioticWolbachiain a murine model of river blindness

“…We found, as has been demonstrated previously, that neutrophil migration does not require immunization [11]. Filarial antigens and Wolbachia both efficiently induced neutrophil migration into the corneal stroma, independent of the immunization status.…”

“…Homologies to human onchocercal keratitis may only be hypothesized as human corneal samples for the investigation of pathology are scarce for obvious reasons. Previous studies using this murine model of Onchocerca keratitis demonstrated that (1) there is not only a predominant Th2 response, with elevated IL-4, IL-5, IgE, IgG1, and eosinophilia, but also an induction of IFNγ [10]; (2) the presence of endosymbiotic Wolbachia is essential for neutrophil recruitment to the corneal stroma and development of corneal haze [7]; (3) Wolbachia-induced corneal inflammation is TLR2 and MyD88 dependent [11,12]; and (4) dendritic cell activation and IFNγ production are dependent on TLR2, whereas Th2-associated responses (IL-5 production, eosinophil infiltration into the cornea) are TLR2 independent [13]. These findings are consistent with the hypothesis that Wolbachia induce Th1-associated responses and neutrophil recruitment through TLR2/MyD88-dependent responses, whereas Th2 responses are Wolbachia independent and may be induced directly by filarial antigens.…”

Human Conjunctival Transcriptome Analysis Reveals the Prominence of Innate Defense inChlamydia trachomatisInfection

“…Extensive work on the mechanism of neutrophil influx into the cornea following infection with Onchocerca volvulus has demonstrated the dependence of this influx on multiple factors originating from cells that are resident in and infiltrate the tissue (28,46). The resulting neutrophil influx and activation was then responsible for keratitis and corneal haze (29). It therefore seems likely that the control of neutrophil recruitment and activation either by adaptive CD4 ϩ Th cells (e.g., Th17 cells) or by chemokines secreted by infected epithelial cells will be crucial, and this requires further investigation.…”

The bacteriaWolbachiain filariae, a biological Russian dolls’ system: new trends in antifilarial treatments

“…the activation of macrophages and their subsequent desensitisation by Wolbachia molecules is dependent both on toll-like receptor (tLr)2 and on the adapter protein MyD88 (Gillette-Ferguson et al, 2006;turner et al, 2006). it was established that Wolbachia-induced inflammation is dependent on tLr2 and tLr6, and partially on tLr1, and that the MyD88/Mal signal transduction pathway is mediated by triF and traM (Hise et al, 2007). recently Wolbachia diacyl lipoproteins were identified as being responsible for tLr2 and tLr6 activation and being involved in proinflammatory cytokine production (turner et al, 2009). current therapeutic approach With antibiotic treatments targeting Wolbachia in the last ten years, investigators have emphasized the association between Wolbachia and filariae and have suggested that the Wolbachia bacteria could provide a novel target for antibiotic-based therapy or a novel antisymbiotic chemotherapy.…”