Wolbachia bacteria in filarial immunity and disease

Lymphatic filarial nematodes are infected with endosymbiotic Wolbachia bacteria. Lipopolysaccharide from these bacteria is the major activator of innate inflammatory responses induced directly by the parasite. Here, we propose a mechanism by which Wolbachia initiates acute inflammatory responses associated with death of parasites, leading to acute filarial lymphangitis and adverse reactions to antifilarial chemotherapy. We also speculate that repeated exposure to acute inflammatory responses and the chronic release of bacteria, results in damage to infected lymphatics and desensitization of the innate immune system. These events will result in an increased susceptibility to opportunistic infections, which cause acute dermatolymphangitis associated with lymphoedema and elephantiasis. The recognition of the contribution of endosymbiotic bacteria to filarial disease could be exploited for clinical intervention by the targeting of bacteria with antibiotics in an attempt to reduce the development of filarial pathology.

Inflammatory responses induced by the filarial nematode Brugia malayi are mediated by lipopolysaccharide-like activity from endosymbiotic Wolbachia bacteria

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)-alpha, interleukin (IL)-1beta, 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-alpha, IL-1beta, and NO responses were not induced in macrophages from lipopolysaccharide (LPS)-nonresponsive C3H/HeJ mice. The production of TNF-alpha 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-alpha 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-alpha 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.

Immunogenicity of recombinant BCG producing the GRA1 antigen from Toxoplasma gondii

Toxoplasmosis is a major parasitic disease, responsible for foetopathy in humans and domestic animals, especially sheep. Toxoplasma gondii infection generally protects immunocompetent hosts against subsequent reinfection, suggesting that efficacious vaccines can be developed against this disease. Excreted/secreted T. gondii antigens have previously been shown to provide immunoprotection in small rodents, and protective immunity is thought to be cell-mediated. Mycobacterium bovis BCG is known to be a good inducer of cellular immunity. In this study, we have developed a BCG strain which produces and secretes GRA1, one of the major excreted/secreted T. gondii antigens. This strain does not carry antibiotic-resistance determinants and is therefore safe for the environment. The intraperitoneal immunisation of OF1 outbred mice with this BCG strain failed to induce GRA1-specific humoral or cellular immune responses and only conferred a very limited degree of protection against challenge with virulent T. gondii. However, in sheep immunised subcutaneously and boosted intravenously, this recombinant BCG strain induced GRA1-specific cell-mediated responses, as evidenced by the proliferation of peripheral blood mononuclear cells and by the production of IFN-gamma, although it failed to elicit GRA1-specific antibody responses. Following oocyst challenge infection, sheep immunised with recombinant BCG exhibited an abbreviated temperature response compared with controls, suggesting partial protection.

Antigen-presenting function and B7 expression of murine sinusoidal endothelial cells and Kupffer cells

BACKGROUND & AIMS

Inflammatory liver disease as well as rejection of liver allografts are thought to be mediated by resident antigen-presenting cells in the liver. At the same time, in vivo antigen presentation in the liver appears to be a more tolerogenic than systemic antigen challenge. The aim of this study was to show and characterize the antigen-presenting capability of sinusoidal endothelial cells and Kupffer cells.

METHODS

Purified murine sinusoidal endothelial cells and Kupffer cells were studied for their ability to serve as accessory cells and antigen-presenting cells by proliferation assays. They were also studied for their expression of interleukin 1 and the B7 costimulatory molecules by Northern blotting, polymerase chain reaction, and flow cytometry.

RESULTS

Both cell types expressed interleukin 1 messenger RNA and could serve equally well as accessory and antigen-presenting cells. B7-2 messenger RNA and surface expression on sinusoidal endothelial cells and on Kupffer cells was shown. Antibodies to the B7 molecules inhibited antigen presentation. Addition of interleukin 10 as a regulatory cytokine secreted by Kupffer cells was suppressive.

CONCLUSIONS

Sinusoidal endothelial cells carry functional B7-2 molecules and can serve as effective antigen-presenting cells. However, antigen presentation by sinusoidal endothelial cells may be locally down-regulated by interleukin 10.