Allergen endotoxins induce T-cell-dependent and non-IgE-mediated nasal hypersensitivity in mice.

BACKGROUND: Allergen-mediated cross-linking of IgE on mast cells/basophils is a well-recognized trigger for type 1 allergic diseases such as allergic rhinitis (AR). However, allergens may not be the sole trigger for AR, and several allergic-like reactions are induced by non-IgE-mediated mechanisms. OBJECTIVE: We sought to describe a novel non-IgE-mediated, endotoxin-triggered nasal type-1-hypersensitivity-like reaction in mice. METHODS: To investigate whether endotoxin affects sneezing responses, mice were intraperitoneally immunized with ovalbumin (OVA), then nasally challenged with endotoxin-free or endotoxin-containing OVA. To investigate the role of T cells and mechanisms of the endotoxin-induced response, mice were adoptively transferred with in vitro-differentiated OVA-specific TH2 cells, then nasally challenged with endotoxin-free or endotoxin-containing OVA. RESULTS: Endotoxin-containing, but not endotoxin-free, OVA elicited sneezing responses in mice independent from IgE-mediated signaling. OVA-specific TH2 cell adoptive transfer to mice demonstrated that local activation of antigen-specific TH2 cells was required for the response. The Toll-like receptor 4-myeloid differentiation factor 88 signaling pathway was indispensable for endotoxin-containing OVA-elicited rhinitis. In addition, LPS directly triggered sneezing responses in OVA-specific TH2-transferred and nasally endotoxin-free OVA-primed mice. Although antihistamines suppressed sneezing responses, mast-cell/basophil-depleted mice had normal sneezing responses to endotoxin-containing OVA. Clodronate treatment abrogated endotoxin-containing OVA-elicited rhinitis, suggesting the involvement of monocytes/macrophages in this response. CONCLUSIONS: Antigen-specific nasal activation of CD4+ T cells followed by endotoxin exposure induces mast cell/basophil-independent histamine release in the nose that elicits sneezing responses. Thus, environmental or nasal residential bacteria may exacerbate AR symptoms. In addition, this novel phenomenon might explain currently unknown mechanisms in allergic(-like) disorders.

Murine allergic rhinitis and nasal Th2 activation are mediated via TSLP- and IL-33-signaling pathways.

Thymic stromal lymphopoietin (TSLP) and IL-33 are epithelium-derived proallergic cytokines that contribute to allergic diseases. Although the involvement of TSLP in allergic rhinitis (AR) is suggested, the exact role of TSLP in AR is poorly understood. Furthermore, the relative contribution of TSLP and IL-33 in nasal allergic responses has not been described. In this study, we examined the roles of TSLP and IL-33 in AR by analyzing acute and chronic AR models. Acute AR mice were intraperitoneally immunized with ragweed, then intranasally challenged with ragweed pollen for four consecutive days. Chronic AR mice were nasally administrated ragweed pollen on consecutive days for 3 weeks. In both models, TSLP receptor (TSLPR)-deficient mice showed defective sneezing responses and reduced serum ragweed-specific IgE levels compared with wild-type (WT) mice. Analyses of bone-marrow chimeric mice demonstrated that hematopoietic cells were responsible for defective sneezing in TSLPR-deficient mice. In addition, FcεRI(+)-cell-specific TSLPR-deficient mice showed partial but significant reduction in sneezing responses. Of note, Th2 activation and nasal eosinophilia were comparable between WT and TSLPR-deficient mice. ST2- and IL-33-deficient mice showed defective Th2 activation and nasal eosinophilia to acute, but not chronic, ragweed exposure. TSLPR and ST2 double-deficient mice showed defective Th2 activation and nasal eosinophilia even after chronic ragweed exposure. These results demonstrate that TSLPR signaling is critical for the early phase response of AR by controlling the IgE-mast-cell/basophil pathway. The IL-33/ST2 pathway is central to nasal Th2 activation during acute allergen exposure, but both TSLPR and ST2 contribute to Th2 responses in chronically allergen-exposed mice.

Requirement of GATA-binding protein 3 for II13 gene expression in IL-18-stimulated Th1 cells.

Recent reports have revealed that CD4(+) T(h) cell subsets have the ability to alter their gene expression pattern in response to extracellular stimuli. We previously highlighted the plasticity of T(h)1 cells by demonstrating that T(h)1 cells gain the capacity to produce IL-3, IL-9, IL-13 and granulocyte macrophage colony-stimulating factor in response to antigen, IL-2 and IL-18, and based on their unique function, we designated these activated T(h)1 cells as 'super T(h)1 cells'. However, the precise molecular mechanism underlying IL-13 production by super T(h)1 cells has not been elucidated. Here, we show that the GATA-binding protein 3 (Gata3) is essentially required for II13 gene expression in super T(h)1 cells. Gata3 is synergistically induced in T-box expressed in T-cells (T-bet)-expressing T(h)1 cells when co-stimulated with anti-CD3, IL-18 and IL-4 through the activation of nuclear factor of activated T cells, nuclear factor kappa-light-chain-enhancer of activated B cells and signal transducer and activator of transcription 6, respectively. However, Gata3 induction is not satisfactory, and additional TCR or anti-CD3 signaling is prerequisite for triggering IL-13 production by Gata3 plus T-bet-expressing T(h)1 cells. These findings suggest that Gata3, which is not originally expressed in T(h)1 cells, alters the cytokine production profile by T(h)1 cells.

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.

Basophils contribute to T(H)2-IgE responses in vivo via IL-4 production and presentation of peptide-MHC class II complexes to CD4+ T cells.

Basophils express major histocompatibility complex class II, CD80 and CD86 and produce interleukin 4 (IL-4) in various conditions. Here we show that when incubated with IL-3 and antigen or complexes of antigen and immunoglobulin E (IgE), basophils internalized, processed and presented antigen as complexes of peptide and major histocompatibility complex class II and produced IL-4. Intravenous administration of ovalbumin-pulsed basophils into naive mice 'preferentially' induced the development of naive ovalbumin-specific CD4+ T cells into T helper type 2 (T(H)2) cells. Mice immunized in this way, when challenged by intravenous administration of ovalbumin, promptly produced ovalbumin-specific IgG1 and IgE. Finally, intravenous administration of IgE complexes rapidly induced T(H)2 cells only in the presence of endogenous basophils, which suggests that basophils are potent antigen-presenting cells that 'preferentially' augment T(H)2-IgE responses by capturing IgE complex.

Regulation of signal transducer and activator of transcription signaling by the tyrosine phosphatase PTP-BL.

Signal Transducer and Activator of Transcription (STAT) proteins are a family of latent cytoplasmic transcription factors that are activated by tyrosine phosphorylation after cytokine stimulation. One mechanism by which STAT signaling is regulated is by dephosphorylation through the action of protein tyrosine phosphatases (PTP). We have identified PTP-Basophil like (PTP-BL) as a STAT PTP. PTP-BL dephosphorylates STAT proteins in vitro and in vivo, resulting in attenuation of STAT-mediated gene activation. In CD4(+) T cells, PTP-BL deficiency leads to increased and prolonged activation of STAT4 and STAT6, and consequently enhanced T helper 1 (Th1) and Th2 cell differentiation. Taken together, our findings demonstrate that PTP-BL is a physiologically important negative regulator of the STAT signaling pathway.

A mechanism underlying STAT4-mediated up-regulation of IFN-gamma induction inTCR-triggered T cells.

IL-12 promotes T(h)1 development/IFN-gamma expression by activating STAT4. However, it is still unclear how STAT4 elicits IFN-gamma promoter activation. Here, we investigated the mechanism by which IL-12-activated STAT4 functions for IFN-gamma induction in TCR-triggered T cells. TCR stimulation induced high levels of IFN-gamma production depending on co-stimulation with IL-12. IL-12 stimulation greatly enhanced the promoter-binding activity of c-Jun/AP-1, a critical transcription factor for IFN-gamma gene expression in wild-type T cells, but not in STAT4-deficient (STAT4(-/-)) T cells. Comparable amounts of c-Jun were induced by TCR stimulation in both wild-type and STAT4(-/-) T cells irrespective of IL-12 co-stimulation. However, c-Jun bound to STAT4 in IL-12-co-stimulated wild-type T cells. c-Jun forming a complex with STAT4 efficiently interacted with the AP-1-related sequence of the IFN-gamma promoter. Such an enhanced c-Jun binding did not occur in STAT4(-/-) T cells. These results show that STAT4 contributes to enhancing IFN-gamma expression by up-regulating the binding of TCR signal-induced AP-1 to the relevant promoter sequence.

Tracking mouse visual pathways with WGA transgene.

By use of wheat germ agglutinin (WGA) cDNA as a transgene, we have succeeded in generating a transgenic mouse line in which the visual pathways can be accurately and reproducibly visualized. The WGA transgene was expressed in the retinal rod bipolar cells under the control of mouse L7 promoter. The transgene product, WGA protein, was transferred from the bipolar cells to the amacrine cells and the ganglion cells across synapses in the retinal neural circuitry and further conveyed along the optic nerve to the visual centers such as the suprachiasmatic nucleus, the lateral geniculate nucleus, the pretectal nucleus and the superior colliculus. By crossing the WGA-expressing transgenic mice with the retinal degeneration mutant mice, we analyzed change in the visual pathways by monitoring WGA immunoreactivity and found that the disorganization process of the visual pathways was relatively slow in spite of the rapid degeneration of the photoreceptor cells. Thus, this transgenic mouse line would provide a useful tool for analyzing phenotypic changes in the visual pathways of various mutant mice.

Differential requirements for JAK2 and TYK2 in T cell proliferation and IFN-gamma production induced by IL-12 alone or together with IL-18.

IL-12 activates TYK2 and Janus kinase (JAK)-2 to induce the phosphorylation of various signal transducers and activators of transcription (STAT) proteins. However, little is known regarding how these JAK exhibit the distinct biological effects of IL-12. Using two JAK inhibitors, tyrphostin A1 (A1) for TYK2 and tyrphostin B42 (B42) for JAK2, we investigated the involvement of JAK2 and TYK2 in IL-12-induced T cell proliferation and IFN-gamma production. B42, but not A1, inhibited T cell proliferation along with down-regulation of IL-12-induced c-Myc expression and STAT5 phosphorylation. In contrast, A1 but not B42 inhibited STAT4/STAT3 phosphorylation and IFN-gamma production. IL-18, but not IL-12, induced activator protein-1 (AP-1) responsible for high levels of IFN-gamma promoter activation. However, this IL-18 effect depended on the interaction of AP-1 with STAT4. A1 prevented AP-1 binding by inhibiting STAT4 involvement and down-regulated synergistic IFN-gamma promoter activation. These results indicate that JAK2 activation is required for IL-12-mediated T cell growth, whereas the TYK2-STAT4 signaling pathway is critical for IFN-gamma expression that is mediated by IL-12 alone and enhanced synergistically by combination with IL-18.

Molecular mechanisms underlying differential contribution of CD28 versus non-CD28 costimulatory molecules to IL-2 promoter activation.

T cell costimulation via CD28 and other (non-CD28) costimulatory molecules induces comparable levels of [(3)H]TdR incorporation, but fundamentally differs in the contribution to IL-2 production. In this study, we investigated the molecular basis underlying the difference between CD28 and non-CD28 costimulation for IL-2 gene expression. Resting T cells from a mutant mouse strain generated by replacing the IL-2 gene with a cDNA encoding green fluorescent protein were stimulated with a low dose of anti-CD3 plus anti-CD28 or anti-non-CD28 (CD5 or CD9) mAbs. CD28 and non-CD28 costimulation capable of inducing potent [(3)H]TdR uptake resulted in high and marginal levels of green fluorescent protein expression, respectively, indicating their differential IL-2 promoter activation. CD28 costimulation exhibited a time-dependent increase in the binding of transcription factors to the NF-AT and NF-kappaB binding sites and the CD28-responsive element of the IL-2 promoter, whereas non-CD28 costimulation did not. Particularly, a striking difference was observed for the binding of NF-kappaB to CD28-responsive element and the NF-kappaB binding site. Decreased NF-kappaB activation in non-CD28 costimulation resulted from the failure to translocate a critical NF-kappaB member, c-Rel, to the nuclear compartment due to the lack of IkappaBbeta inactivation. These observations suggest that unlike CD28 costimulation, non-CD28 costimulation fails to sustain IL-2 promoter activation and that such a failure is ascribed largely to the defect in the activation of c-Rel/NF-kappaB.

Synergy of IL-12 and IL-18 for IFN-gamma gene expression: IL-12-induced STAT4 contributes to IFN-gamma promoter activation by up-regulating the binding activity of IL-18-induced activator protein 1.

IL-12 and IL-18 synergistically enhance IFN-gamma mRNA transcription by activating STAT4 and AP-1, respectively. However, it is still unknown how STAT4/AP-1 elicit IFN-gamma promoter activation. Using an IL-12/IL-18-responsive T cell clone, we investigated the mechanisms underlying synergistic enhancement of IFN-gamma mRNA expression induced by these two cytokines. Synergy was observed in a reporter gene assay using an IFN-gamma promoter fragment that binds AP-1, but not STAT4. An increase in c-Jun, a component of AP-1, in the nuclear compartment was elicited by stimulation with either IL-12 or IL-18, but accumulation of serine-phosphorylated c-Jun was induced only by IL-18 capable of activating c-Jun N-terminal kinase. The binding of AP-1 to the relevant promoter sequence depended on the presence of STAT4. STAT4 bound with c-Jun, and a phosphorylated c-Jun-STAT4 complex most efficiently interacted with the AP-1-relevant promoter sequence. Enhanced cobinding of STAT4 and c-Jun to the AP-1 sequence was also observed when activated lymph node T cells were exposed to IL-12 plus IL-18. These results show that STAT4 up-regulates AP-1-mediated IFN-gamma promoter activation without directly binding to the promoter sequence, providing a mechanistic explanation for IL-12/IL-18-induced synergistic enhancement of IFN-gamma gene expression.