Contribution of IL-18 to eosinophilic airway inflammation induced by immunization and challenge with Staphylococcus aureus proteins.

We previously reported that intranasal challenge with ovalbumin (OVA) plus IL-18 induces airway hyperresponsiveness (AHR) and eosinophilic airway inflammation in mice with OVA-specific T(h)1 cells. These two conditions can be prevented by neutralizing anti-IFN-gamma and anti-IL-13 antibodies, respectively. The mice develop AHR and eosinophilic airway inflammation after challenge with OVA plus LPS instead of IL-18 and endogenous IL-18 is known to be involved. In contrast, IL-18 does not facilitate these changes in mice possessing OVA-specific T(h)2 cells. Here, we investigated whether IL-18 is involved in the development of asthma in mice immunized and challenged with bacterial proteins. Upon intranasal exposure to protein A (SpA) derived from Staphylococcus aureus, mice immunized with SpA exhibited AHR and peribronchial eosinophilic inflammation if IFN-gamma or IL-13 were present, respectively. The CD4(+) T cells from draining lymph nodes (DLNs) of the SpA-immunized and -challenged mice produced a robust IFN-gamma and IL-13 in response to immobilized anti-CD3 antibodies. Treatment with neutralizing anti-IL-18 antibodies prevented asthmatic inflammation concomitant with their impaired potential to express IFN-gamma and IL-13. Furthermore, naive mice that received the CD4(+) T cells from DLNs of SpA-immunized mice developed airway inflammation depending upon the presence of IL-18. Immunodeficient mice that received human PBMCs, which had been stimulated with SpA in vitro, developed dense peribronchial accumulation of human CD4(+) T cells upon SpA challenge. Neutralizing anti-human IL-18 antibodies protected against this airway inflammation. These results suggest the importance of IL-18 for the development of asthmatic inflammation associated with airway exposure to bacterial proteins.

Contribution of TIR domain-containing adapter inducing IFN-beta-mediated IL-18 release to LPS-induced liver injury in mice.

BACKGROUND/AIMS: After treatment with heat-killed Propionibacterium acnes mice show dense hepatic granuloma formation. Such mice develop liver injury in an interleukin (IL)-18-dependent manner after challenge with a sublethal dose LPS. As previously shown, LPS-stimulated Kupffer cells secrete IL-18 depending on caspase-1 and Toll-like receptor (TLR)-4 but independently of its signal adaptor myeloid differentiation factor 88 (MyD88), suggesting importance of another signal adaptor TIR domain-containing adapter inducing IFN-beta (TRIF). Nalp3 inflammasome reportedly controls caspase-1 activation. Here we investigated the roles of MyD88 and TRIF in P. acnes-induced hepatic granuloma formation and LPS-induced caspase-1 activation for IL-18 release. METHODS: Mice were sequentially treated with P. acnes and LPS, and their serum IL-18 levels and liver injuries were determined by ELISA and ALT/AST measurement, respectively. Active caspase-1 in LPS-stimulated Kupffer cells was determined by Western blotting. RESULTS: Macrophage-ablated mice lacked P. acnes-induced hepatic granuloma formation and LPS-induced serum IL-18 elevation and liver injury. Myd88(-/-) Kupffer cells, but not Trif(-/-) cells, exhibited normal caspase-1 activation upon TLR4 engagement in vitro. Myd88(-/-) mice failed to develop hepatic granulomas after P. acnes treatment and liver injury induced by LPS challenge. In contrast, Trif(-/-) mice normally formed the hepatic granulomas, but could not release IL-18 or develop the liver injury. Nalp3(-/-) mice showed the same phenotypes of Trif(-/-) mice. CONCLUSIONS: Propionibacterium acnes treatment MyD88-dependently induced hepatic granuloma formation. Subsequent LPS TRIF-dependently activated caspase-1 via Nalp3 inflammasome and induced IL-18 release, eventually leading to the liver injury.

Persistent secretion of IL-18 in the skin contributes to IgE response in mice.

After exposure of the skin to microbes, the host develops skin-specific inflammation and an acquired immune response, in which keratinocytes (KC) and Langerhans cells play critical roles respectively. We established two animal models. (i) We examined the importance of KC-derived IL-18 for the systemic IgE response by using a skin transplantation model. As previously reported, transgenic mice (KCASP1Tg), that over-express caspase-1 in their KC, display high serum levels of IgE, and spontaneously develop chronic dermatitis by production of IL-18 and IL-1beta. We examined the capacity of transplantation of cutaneous lesions from KCASP1Tg to induce IgE production in wild-type or mutant mice with a syngeneic background. Transplantation of active cutaneous lesions, that expressed high levels of IL-18 and IL-1beta, induced long-lasting IgE production in wild-type mice without elevation of circulating IL-18 and IL-1beta. Furthermore, IL-18R-, CD4- or stat6-deficient mice transplanted with the lesions did not produce IgE, indicating that this IgE response is initiated by IL-18, and dependent on host-derived CD4(+) T cells and stat6. (ii) We investigated IL-18 secretion from KC upon stimulation with microbe products. Freshly isolated KC from wild-type mice secreted IL-18 in response to Protein A purified from Cowan 1 strain of Staphylococcus aureus (SpA), which often exacerbates human skin diseases, including atopic dermatitis. Cutaneous application of SpA increased serum levels of IL-18 and IgE. These results indicate that local accumulation of IL-18 triggers systemic IgE responses without exposure to antigen.

A regulatory role for suppressor of cytokine signaling-1 in T(h) polarization in vivo.

Suppressor of cytokine signaling (SOCS)-1 is an inhibitory molecule for JAK, and its deficiency in mice leads to lymphocyte-dependent multi-organ disease and perinatal death. Crossing of SOCS-1(-/-) mice on an IFN-gamma(-/-), STAT1(-/-) and STAT6(-/-) background revealed that the fatal disease of SOCS-1(-/-) mice is also dependent on IFN-gamma/STAT1 and IL-4/STAT6 signaling pathways. Since IFN-gamma and IL-4 are representative T(h)1 and T(h)2 cytokines respectively, here we investigated the role of SOCS-1 in T(h) differentiation. Freshly isolated SOCS-1(-/-) CD4(+) T cells stimulated with anti-CD3 rapidly produced larger amounts of IFN-gamma and IL-4 than control cells, suggesting that these mutant T cells had already differentiated into T(h)1 and T(h)2 cells in vivo. In addition, SOCS-1(+/-) CD4(+) T cells cultured in vitro produced significantly larger amounts of IFN-gamma and IL-4 than SOCS-1(+/+) cells. Similarly, SOCS-1(+/-) CD4(+) T cells produced more IFN-gamma and IL-4 than SOCS-1(+/+) cells after infection with Listeria monocytogenes and Nippostrongyrus braziliensis respectively. Since IL-12-induced STAT4 and IL-4-induced STAT6 activation is sustained in SOCS-1(-/-) T cells, the enhanced T(h) functions in SOCS-1(-/-) and SOCS-1(+/-) mice appear to be due to the enhanced effects of these cytokines. These results suggest that SOCS-1 plays a regulatory role in both T(h)1 and T(h)2 polarizations.

IL-18 contributes to the spontaneous development of atopic dermatitis-like inflammatory skin lesion independently of IgE/stat6 under specific pathogen-free conditions.

Atopic dermatitis (AD) is a pruritic inflammatory skin disease. Because IL-18 directly stimulates T cells and mast cells to release AD-associated molecules, Th2 cytokines, and histamine, we investigated the capacity of IL-18 to induce AD-like inflammatory skin disease by analyzing KIL-18Tg and KCASP1Tg, which skin-specifically overexpress IL-18 and caspase-1, respectively. They spontaneously developed relapsing dermatitis with mastocytosis and Th2 cytokine accumulation accompanied by systemic elevation of IgE and histamine. Stat6-deficient KCASP1Tg displayed undetectable levels of IgE but manifested the same degree of cutaneous changes, whereas IL-18-deficient KCASP1Tg evaded the dermatitis, suggesting that IL-18 causes the skin changes in the absence of IgE/stat6. KIL-18Tg and IL-1-deficient KCASP1Tg took longer to display the lesion than KCASP1Tg. Thus, AD-like inflammation is initiated by overrelease of IL-18 and accelerated by IL-1. Our present study might provide insight into understanding the pathogenesis of and establishing therapeutics for chronic inflammatory skin diseases including AD.