Allergen-specific Th1 cells counteract efferent Th2 cell-dependent bronchial hyperresponsiveness and eosinophilic inflammation partly via IFN-gamma

Th2 T cell immune-driven inflammation plays an important role in allergic asthma. We studied the effect of counterbalancing Th1 T cells in an asthma model in Brown Norway rats that favors Th2 responses. Rats received i.v. transfers of syngeneic allergen-specific Th1 or Th2 cells, 24 h before aerosol exposure to allergen, and were studied 18-24 h later. Adoptive transfer of OVA-specific Th2 cells, but not Th1 cells, and OVA, but not BSA exposure, induced bronchial hyperresponsiveness (BHR) to acetylcholine and eosinophilia in a cell number-dependent manner. Importantly, cotransfer of OVA-specific Th1 cells dose-dependently reversed BHR and bronchoalveolar lavage (BAL) eosinophilia, but not mucosal eosinophilia. OVA-specific Th1 cells transferred alone induced mucosal eosinophilia, but neither BHR nor BAL eosinophilia. Th1 suppression of BHR and BAL eosinophilia was allergen specific, since cotransfer of BSA-specific Th1 cells with the OVA-specific Th2 cells was not inhibitory when OVA aerosol alone was used, but was suppressive with OVA and BSA challenge. Furthermore, recipients of Th1 cells alone had increased gene expression for IFN-gamma in the lungs, while those receiving Th2 cells alone showed increased IL-4 mRNA. Importantly, induction of these Th2 cytokines was inhibited in recipients of combined Th1 and Th2 cells. Anti-IFN-gamma treatment attenuated the down-regulatory effect of Th1 cells. Allergen-specific Th1 cells down-regulate efferent Th2 cytokine-dependent BHR and BAL eosinophilia in an asthma model via mechanisms that depend on IFN-gamma. Therapy designed to control the efferent phase of established asthma by augmenting down-regulatory Th1 counterbalancing mechanisms should be effective.     

Contribution of Th1 and Th2 cells to protection and pathology in experimental models of granulomatous lung disease

Mice that had received adoptive transfer of DO11.10 TCR transgenic T cells polarized toward a Th1 or a Th2 phenotype were challenged with Ag-coated beads or with recombinant Mycobacterium tuberculosis expressing the OVA determinant. The resulting bead-induced pulmonary granulomas reflected the phenotype of the adoptively transferred T cells, with the Th2 cells promoting a fibrotic reaction. Mice receiving Th1 cells mounted an epitope-specific protective response to challenge with recombinant M. tuberculosis. Th2 recipients were characterized by enhanced weight loss and lung fibrosis during acute high-dose infection. The combination of TCR transgenic T cells and epitope-tagged mycobacteria provides a novel experimental model for investigation of the pathogenesis of tuberculosis.     

CD8 T cells inhibit IgE via dendritic cell IL-12 induction that promotes Th1 T cell counter-regulation.

Th1 and Th2 cells are counterinhibitory; their balance determines allergic sensitization. We show here that CD8 T cell subsets break these rules as both T cytotoxic (Tc)1 and Tc2 cells promote Th1 over Th2 immunity. Using IL-12(-/-), IFN-gamma(-/-), and OVA(257-264)-specific Valpha2Vbeta5 TCR-transgenic mice, we have identified the key steps involved. OVA-specific IFN-gamma(-/-) CD8 T cells inhibited IgE responses equivalent to wild-type CD8 T cells (up to 98% suppression), indicating that CD8 T cell-derived IFN-gamma was not required. However, OVA-specific CD8 T cells could not inhibit IgE in IFN-gamma(-/-) recipients unless reconstituted with naive, wild-type CD4 T cells, suggesting that CD4 T cell-derived IFN-gamma did play a role. Transfer of either Tc1 or Tc2 Valpha2Vbeta5 TCR-transgenic CD8 T cells inhibited IgE and OVA-specific Th2 cells while promoting OVA-specific Th1 cell responses, suggesting a potential role for a type 1 inducing cytokine such as IL-12. CD8 T cells were shown to induce IL-12 in OVA(257-264)-pulsed dendritic cells (DC) in vitro. Furthermore, CD8 T cells were unable to inhibit IgE responses in IL-12(-/-) recipients without the addition of naive, wild-type DC, thus demonstrating a pivotal role for IL-12 in this mechanism. These data reveal a mechanism of IgE regulation in which CD8 T cells induce DC IL-12 by an IFN-gamma-independent process that subsequently induces Th1 and inhibits Th2 cells. Th1 cell IFN-gamma is the final step that inhibits B cell IgE class switching. This demonstrates a novel regulatory network through which CD8 T cells inhibit allergic sensitization.     

Modulation of Th2 responses by peptide analogues in a murine model of allergic asthma: amelioration or deterioration of the disease process depends on the Th1 or Th2 skewing characteristics of the therapeutic peptide

Allergen-specific CD4+ Th2 cells play an important role in the immunological processes of allergic asthma. Previously we have shown that, by using the immunodominant epitope OVA323-339, peptide immunotherapy in a murine model of OVA induced allergic asthma, stimulated OVA-specific Th2 cells, and deteriorated airway hyperresponsiveness and eosinophilia. In the present study, we defined four modulatory peptide analogues of OVA323-339 with comparable MHC class II binding affinity. These peptide analogues were used for immunotherapy by s.c. injection in OVA-sensitized mice before OVA challenge. Compared with vehicle-treated mice, treatment with the Th2-skewing wild-type peptide and a Th2-skewing partial agonistic peptide (335N-A) dramatically increased airway eosinophilia upon OVA challenge. In contrast, treatment with a Th1-skewing peptide analogue (336E-A) resulted in a significant decrease in airway eosinophilia and OVA-specific IL-4 and IL-5 production. Our data show for the first time that a Th1-skewing peptide analogue of a dominant allergen epitope can modulate allergen-specific Th2 effector cells in an allergic response in vivo. Furthermore, these data suggest that the use of Th1-skewing peptides instead of wild-type peptide may improve peptide immunotherapy and may contribute to the development of a successful and safe immunotherapy for allergic patients.     

Using tolerance induced via the anterior chamber of the eye to inhibit Th2-dependent pulmonary pathology

Anterior chamber-associated immune deviation (ACAID), a manifestation of ocular immune privilege, prevents Th1-dependent delayed hypersensitivity from developing in response to eye-derived Ags, thereby preserving vision. Since Th2-type cells have recently been shown to mediate destructive inflammation of the cornea, we wondered whether pre-emptive induction of ACAID could inhibit Th2 responses. Using a murine model of OVA -specific, Th2-dependent pulmonary inflammation, we pretreated susceptible mice by injecting OVA alone into the anterior chamber, or by injecting OVA-pulsed, TGF-beta2-treated peritoneal exudate cells i.v. These mice were then immunized with OVA plus alum strategy that generates Th2-mediated OVA-specific pulmonary pathology. When pretreated mice were challenged intratracheally with OVA, their bronchoalveolar lavage fluids contained far fewer eosinophils and significantly less IL-4, IL-5, and IL-13 compared with that of positive, nonpretreated controls. Similarly, lung-draining lymph node cells of pretreated mice secreted significantly less IL-4, IL-5, and IL-13 when challenged in vitro with OVA. Moreover, sera from pretreated mice contained much lower titers of OVA-specific IgE Abs. We conclude that Ags injected into the anterior chamber of the eye impair both Th1 and Th2 responses. These results reduce the likelihood that ACAID regulates Th1 responses via a Th2-like mechanism. Thus, immune privilege of the eye regulates inflammation secondary to both Th1- and Th2-type immune responses.     

When engineered to produce latent TGF-beta1, antigen specific T cells down regulate Th1 cell-mediated autoimmune and Th2 cell-mediated allergic inflammatory processes

To determine whether T cells which produce large amounts of latent TGF-beta1 are capable of down-regulating autoimmune and allergic disease, myelin basic protein (MBP)-specific and ovalbumin (OVA)-specific BALB/c cloned Th1 cells were transduced with cDNA for murine TGF-beta1 by coculture with fibroblasts producing a genetically engineered retrovirus. The transduced MBP-specific Th1 cells were found to lose the capacity to provoke EAE in BALB/c mice, and to gain instead the ability to protect against EAE in (SJLxBALB/c) F1 mice immunized with proteolipid protein (PLP). This protective effect was not obtained with OVA-specific TGF-beta1 transduced Th1 cells. The transduced OVA-specific Th1 cells did protect against airway hyperreactivity induced by Th2-cell mediated responses to inhaled OVA. This effect was again antigen specific and it also could not be obtained with untransduced OVA-specific Th1 cells. In both cases these effects of antigen specific TGF-beta1 transduced T cells were nullified by administration of neutralizing anti-TGF-beta mAb. Thus, the antigen specificity of the cloned T cells allows the site-specific local delivery of therapeutic active TGF-beta1 to both Th1 and Th2 cell-mediated inflammatory infiltrates.     

An essential role for IL-18 in CD8 T cell-mediated suppression of IgE responses

The ability of CD8 T cells to suppress IgE responses is well established. Previously, we demonstrated that CD8 T cells inhibit IgE responses via the induction of IL-12, which promotes Th1 and suppresses Th2 responses. In this study, we show that IL-18 also plays an essential role in IgE suppression. In vitro, IL-18 synergized with IL-12 to promote Th1/T cytotoxic 1 and inhibit Th2/T cytotoxic 2 differentiation. OVA-specific TCR transgenic (OT-I) CD8 cells induced both IL-12 and IL-18 when cultured with OVA(257-264) peptide-pulsed dendritic cells. In vivo, IL-18(-/-) mice exhibited higher IgE and IgG1 levels compared with wild-type mice after immunization with OVA/alum. Furthermore, adoptive transfer of CD8 T cells from OVA-primed mice suppressed IgE responses in OVA/alum-immunized mice, but not in IL-18(-/-) mice. IgE suppression in IL-18(-/-) mice was restored if CD8 T cells were coadoptively transferred with IL-18-competent wild-type bone marrow dendritic cell progenitors, demonstrating an essential role of IL-18 in CD8 T cell-mediated suppression of IgE responses. The data suggest that CD8 T cells induce IL-18 production during a cognate interaction with APCs that synergizes with IL-12 to promote immune deviation away from the allergic phenotype. Our data identify IL-18 induction as a potentially useful target in immunotherapy of allergic disease.     

The role of B cells in the development of CD4 effector T cells during a polarized Th2 immune response

Previous studies have suggested that B cells promote Th2 cell development by inhibiting Th1 cell differentiation. To examine whether B cells are directly required for the development of IL-4-producing T cells in the lymph node during a highly polarized Th2 response, B cell-deficient and wild-type mice were inoculated with the nematode parasite, Nippostrongylus brasiliensis. On day 7, in the absence of increased IFN-gamma, IL-4 protein and gene expression from CD4 T cells in the draining lymph nodes were markedly reduced in B cell-deficient mice and could not be restored by multiple immunizations. Using a DO11.10 T cell adoptive transfer system, OVA-specific T cell IL-4 production and cell cycle progression, but not cell surface expression of early activation markers, were impaired in B cell-deficient recipient mice following immunization with N. brasiliensis plus OVA. Laser capture microdissection and immunofluorescent staining showed that pronounced IL-4 mRNA and protein secretion by donor DO11.10 T cells first occurred in the T cell:B cell zone of the lymph node shortly after inoculation of IL-4-/- recipients, suggesting that this microenvironment is critical for initial Th2 cell development. Reconstitution of B cell-deficient mice with wild-type naive B cells, or IL-4-/- B cells, substantially restored Ag-specific T cell IL-4 production. However, reconstitution with B7-1/B7-2-deficient B cells failed to rescue the IL-4-producing DO11.10 T cells. These results suggest that B cells, expressing B7 costimulatory molecules, are required in the absence of an underlying IFN-gamma-mediated response for the development of a polarized primary Ag-specific Th2 response in vivo.     

Regulation of pulmonary T cell responses to inhaled antigen: role in Th1- and Th2-mediated inflammation.

DO11.10 transgenic mice, expressing an OVA-specific TCR, were used to study pulmonary T cell responses to inhaled Ags. Before OVA inhalation, the activation of lung parenchymal T cells elicited both strong proliferative responses and IL-2 production. However, following Ag inhalation the proliferative responses of the lung T cells, when restimulated in vitro with OVA323-339 peptide or immobilized anti-CD3, were severely attenuated and associated with a decrease in the level of production of IL-2 but not IFN-gamma. Such immune regulation was tissue-specific, because T cell responses in the lymph nodes and spleens were normal. This dramatic aerosol-induced attenuation of parenchymal T cell proliferation was also observed in BALB/c mice immunized with OVA and in BALB/c mice following adoptive transfer of DO11.10 T cells bearing either a Th1 or Th2 phenotype. In mice that had received Th2 cells, the reduced proliferative responses were associated with a decrease in IL-2 expression but augmented IL-4 and IL-5 production. Invariably, the inhibition of proliferation was a consequence of the action of F4/80+ interstitial macrophages and did not involve alveolar macrophages or their products. These observations demonstrate that clonal expansion of T cells in the lung compartment is prevented following the onset of either Th1- or Th2-mediated inflammation. This form of immune regulation, which appears as a selective defect in IL-2-driven proliferation, may serve to prevent the development of chronic pulmonary lymphoproliferative responses.     

T regulatory cells 1 inhibit a Th2-specific response in vivo

We recently described a new population of CD4(+) regulatory T cells (Tr1) that inhibits proliferative responses of bystander T cells and prevents colitis induction in vivo through the secretion of IL-10. IL-10, which had been primarily described as a Th2-specific cytokine inhibiting Th1 responses, has displayed in several models a more general immune suppression on both types of effector T cell responses. Using an immediate hypersensitivity model in which BALB/c mice immunized with OVA (alum) normally generate Th2-dominated responses, we examined the ability of OVA-specific Tr1 T cell clones to inhibit OVA-specific cytokines and Ab responses. In contrast to Th2 or Th1 T cell clones, transfer of Tr1 T cell clones coincident with OVA immunization inhibited Ag-specific serum IgE responses, whereas IgG1 and IgG2a synthesis were not affected. This specific inhibition was mediated in part through IL-10 secretion as anti-IL-10 receptor Abs treatment reverted the inhibitory effect of Tr1 T cell clones. Although specifically targeted to IgE responses, Tr1 clones' inhibitory effects were more profound as they affected Ag-specific Th2 cell priming both in term of proliferative responses and cytokine secretion. These results suggest that regulatory T cells may play a fundamental role in maintaining the balance of the immune system to prevent allergic disorders.     

IgE cross-linking or lipopolysaccharide treatment induces recruitment of Th2 cells to the lung in the absence of specific antigen

We previously showed that Th1 cells can increase recruitment of Th2 cells to the lungs even in the absence of the Th2-specific Ag. The fact that Th2 recruitment is independent from the Th2 cell Ag suggested that Th1 cells may support Th2 cell recruitment using their Ag-nonspecific proinflammatory functions. To investigate the potential for inflammatory stimuli that are distinct from Ag-specific signals to affect the recruitment of T cells, we tested whether cross-linking of IgE or treatment with LPS modulated influx of Th2 cells into the airways in the presence or absence of inhaled Ag. When naive mice that had been treated with OVA-specific Th2 cells and passively sensitized with anti-DNP IgE were challenged by intranasal administration of either DNP-haptenated OVA or DNP-BSA, increased numbers of Th2 cells were recruited to the lung compared with mice challenged intranasally with OVA alone. Intranasal administration of LPS also increased recruitment of Th2 cells to the airways. These two distinct inflammatory stimuli increased the numbers of recruited Th2 cells equally with or without concurrent challenge using the cognate Th2 Ag. This Ag-independent recruitment of Th2 cells to the lung was not associated with localization of these cells to the regional lymph nodes and was independent of Th2 cell activation. Interestingly, P- or E-selectin contributed to Th2 cell recruitment to the lung. These data suggest that Th2 cells of the adaptive immune response are similar to cells of the innate immune response in their lack of requirement for protein Ag to initiate cell recruitment. They demonstrate further that recruitment can occur independently of Ag-dependent activation.     

Nippostrongylus brasiliensis can induce B7-independent antigen-specific development of IL-4-producing T cells from naive CD4 T cells in vivo

Th2 immune responses to a number of infectious pathogens are dependent on B7-1/B7-2 costimulatory molecule interactions. We have now examined the Th2 immune response to Nippostrongylus brasiliensis (Nb) in B7-1/B7-2(-/-) mice and show that Th2 effector cells develop that can mediate worm expulsion and produce substantial Th2 cytokines comparable with wild-type infected mice; however, in marked contrast, B cell Ag-specific Ab production is abrogated after B7 blockade. To examine the mechanism of T cell activation, OVA-specific DO11.10 T cells were transferred to recipient mice, which were then immunized with a combination of Nb plus OVA or either alone. Only the combination of Nb plus OVA triggered T cell differentiation to OVA-specific Th2 cells, suggesting that Nb acts as an adjuvant to stimulate Ag-specific naive T cells to differentiate to effector Th2 cells. Furthermore, using the DO11.10 TCR-transgenic T cell adoptive transfer model, we show that blocking B7-1/B7-2 interactions does not impair nonparasite Ag-specific DO11.10 Th2 cell differentiation; however, DO11.10 T cell cycle progression and migration to the B cell zone are inhibited.     

IL-2 and autocrine IL-4 drive the in vivo development of antigen-specific Th2 T cells elicited by nematode parasites

The intestinal nematode parasite, Nippostrongylus brasiliensis, triggers potent type 2 immunity. Using OVA peptide as a model Ag, we have examined the adjuvant effects of this parasite on the in vivo development of Ag-specific Th2 cells from naive DO11.10 T cells. Our findings show that Th2 cells can develop from transferred naive OVA-specific DO11.10 T cells in recipient IL-4-/- mice inoculated with N. brasiliensis plus OVA. However, autocrine IL-4 is required for in situ Th2 cell differentiation since transferred IL-4Ralpha-deficient DO11.10 T cells showed greatly reduced Th2 cell development in inoculated IL-4-/- recipient mice. Surprisingly, we also found that IL-2 blockade promoted B7-dependent T cell cycling, but inhibited the development of OVA-specific Th2 cells. Furthermore, the effects of IL-2 occurred independently of CD25+ T regulatory cells. These studies establish a previously unrecognized requirement for autocrine IL-4 and IL-2 in Th2 responses elicited by nematode parasites.     

Orally induced peripheral nonresponsiveness is maintained in the absence of functional Th1 or Th2 cells

Intragastric administration of soluble protein Ags results in peripheral tolerance to the fed Ag. To examine the role of cytokine regulation in the induction of oral tolerance, we fed OVA to mice deficient in Th1 (Stat 4-/-) and Th2 (Stat 6-/-) cells and compared their response to that of normal BALB/c controls. We found that, in spite of these deficiencies, OVA-specific peripheral cell-mediated and humoral nonresponsiveness was maintained in both Stat 4-/- and Stat 6-/- mice. In the mucosa, both Peyer's patch T cell proliferative responses and OVA-specific fecal IgA were reduced in Stat 4-/- and Stat 6-/- mice fed OVA but not in normal BALB/c controls. Mucosal, but not peripheral, nonresponsiveness was abrogated by the inclusion of a neutralizing Ab to TGF-beta in the culture medium. Our results show that, in the periphery, tolerance to oral Ag can be induced in both a Th1- or Th2-deficient environment. In the mucosa, however, the absence of Th1 and Th2 cytokines can markedly affect this response, perhaps by regulation of TGF-beta-secreting cells.     

Contrasting effects of acute and chronic gastro-intestinal helminth infections on a heterologous immune response in a transgenic adoptive transfer model

We have previously found that co-immunisation with ovalbumin (OVA) and the body fluid of the helminth Ascaris suum inhibited an OVA-specific delayed type hypersensitivity (DTH) response by reducing OVA-specific CD4+ T lymphocyte proliferation via an IL-4 independent mechanism. In the present study, we determined whether parasite infections themselves could induce similar changes to peripheral immunisation by examining the modulation of OVA-specific immune responses during acute and chronic helminth infections. Surprisingly, an acute infection with Trichinella spiralis, but not a chronic infection with Heligmosomoides polygyrus, inhibited the OVA-specific DTH reaction. Correspondingly, the T helper 1 (Th1) OVA-specific response was decreased in mice infected with T. spiralis, but not with H. polygyrus. Inhibition of the Th1 response may be a result of a shift in the Th1/Th2 balance as although both H. polygyrus and T. spiralis infected mice induced a Th2 OVA-specific response, that exhibited by T. spiralis was more potent. Furthermore, although IL-10 secretion upon OVA restimulation was similarly increased by both infections, production of this immunoregulatory cytokine may play a role in the suppression of immune responses observed with T. spiralis infection depending on the context of its release. Interestingly, analysis of the OVA-specific T lymphocyte division by carboxyfluorescein diacetate succinimidyl ester (CFSE) staining revealed that gastro-intestinal infection with the acute helminth T. spiralis, but not with chronic H. polygyrus, inhibited the systemic immune response by significantly inhibiting the antigen-specific T cell proliferation during the primary response, a mechanism similar to that observed when A. suum parasite extracts were directly mixed with the OVA during immunisation in our previous studies.     

CD8+ T cell-mediated airway hyperresponsiveness and inflammation is dependent on CD4+IL-4+ T cells

CD4+ T cells, particularly Th2 cells, play a pivotal role in allergic airway inflammation. However, the requirements for interactions between CD4+ and CD8+ T cells in airway allergic inflammation have not been delineated. Sensitized and challenged OT-1 mice in which CD8+ T cells expressing the transgene for the OVA(257-264) peptide (SIINFEKL) failed to develop airway hyperresponsiveness (AHR), airway eosinophilia, Th2 cytokine elevation, or goblet cell metaplasia. OT-1 mice that received naive CD4+IL-4+ T cells but not CD4+IL-4- T cells before sensitization developed all of these responses to the same degree as wild-type mice. Moreover, recipients of CD4+IL-4+ T cells developed significant increases in the number of CD8+IL-13+ T cells in the lung, whereas sensitized OT-1 mice that received primed CD4+ T cells just before challenge failed to develop these responses. Sensitized CD8-deficient mice that received CD8+ T cells from OT-1 mice that received naive CD4+ T cells before sensitization increased AHR and eosinophil numbers in bronchoalveolar lavage fluid when challenged with allergen. In contrast, sensitized CD8-deficient mice receiving CD8+ T cells from OT-1 mice without CD4+ T cells developed reduced AHR and eosinophil numbers in bronchoalveolar lavage fluid when challenged. These data suggest that interactions between CD4+ and CD8+ T cells, in part through IL-4 during the sensitization phase, are essential to the development of CD8+IL-13+ T cell-dependent AHR and airway allergic inflammation.     

Invariant NKT Cells Act as an Adjuvant to Enhance Th2 Inflammatory Response in an OVA-Induced Mouse Model of Asthma

Background

Invariant natural killer T cells (iNKT cells) are a unique subset of T lymphocytes and are considered to play an important role in the development of allergic bronchial asthma. Recently, iNKT cells were shown to play an immunoregulatory role in CD4⁺ and CD8⁺ T cell-mediated adaptive immune response. Allergen-specific Th2 inflammatory responses are an important part of the adaptive immune response in asthma. However, the regulatory functions of the Th2 inflammatory response in asthma have not been studied in detail.

Method

In this study, we have investigated the regulatory functions of iNKT cells on the Th2 inflammatory response in an ovalbumin (OVA)-induced murine model of asthma.

Results

Our results demonstrate that α-Galactosylceramide (α-GalCer) administration activated iNKT cells but could not induce the Th2 inflammatory response in wild-type (WT) mice. In the OVA-induced asthma model, α-GalCer administration and adoptive transfer of iNKT cells significantly augmented the Th2 inflammatory responses, including elevated inflammatory cell infiltration in the lung and bronchoalveolar lavage fluid (BALF); increased levels of IL-4, IL-5, and IL-13 in the BALF and splenocyte culture supernatant; and increased serum levels of OVA-specific IgE and IgG1. In addition, the Th2 inflammatory response was reduced, but not completely abrogated in CD1d^-/- mice immunized and challenged with OVA, compared with WT mice.

Conclusion

These results suggest that iNKT cells may serve as an adjuvant to enhance Th2 inflammatory response in an OVA-induced murine model of asthma.     

Antigen-nonspecific recruitment of Th2 cells to the lung as a mechanism for viral infection-induced allergic asthma

Respiratory viral infections have been shown to trigger exacerbations of asthma; however, the mechanism by which viral Th1-type inflammation exacerbates an allergic Th2-type disease remains unclear. We have previously shown that although adoptively transferred Th2 cells are inefficiently recruited to the lung in response to Ag, cotransfer of Th1 cells can increase accumulation of Th2 cells. In this study, we show that respiratory viral infection increases recruitment of resting Th2 cells specific for OVA even in the absence of OVA challenge. These findings suggest that the mechanism by which Th1-type inflammation enhances allergy is via an effect on recruitment. To study the role of the antigenic specificity of Th1 cells in the enhancement of Th2 cell recruitment and to determine whether virus-induced recruitment of OVA-specific Th2 cells may involve Th1 cells specific to a different Ag, we tested whether hen egg lysozyme-specific Th1 cells could synergize with OVA-specific Th2 cells. Challenge of mice that had received adoptively transferred Th1 cells plus Th2 cells induced the expression of inflammatory chemokines in the lung and increased both recruitment and activation of Th2 cells, leading to eosinophil recruitment, even in the absence of challenge with the Th2 Ag. Interestingly, as IL-5 supports eosinophilia, culture of resting Th2 cells with fresh APC induced production of IL-5 in the absence of specific Ag. Thus, Ag-specific activation of Th1 cells enhances the recruitment potential of the lung leading to recruitment and activation of Th2 cells. This implies that circulating Th2 cells in allergic individuals could enter the lungs in response to infection or inflammation and become activated to trigger allergy.     

Topical superantigen exposure induces epidermal accumulation of CD8+ T cells, a mixed Th1/Th2-type dermatitis and vigorous production of IgE antibodies in the murine model of atopic dermatitis

Patients with atopic dermatitis (AD) have repeated cutaneous exposure to both environmental allergens and superantigen-producing strains of Staphylococcus aureus. We used a murine model of AD to investigate the role of staphylococcal enterotoxin B (SEB) in the modulation of allergen-induced skin inflammation. Mice were topically exposed to SEB, OVA, a combination of OVA and SEB (OVA/SEB), or PBS. Topical SEB and OVA/SEB exposure induced epidermal accumulation of CD8+ T cells and TCRVbeta8+ cells in contrast to OVA application, which induced a mainly dermal infiltration of CD4+ cells. SEB and OVA/SEB exposure elicited a mixed Th1/Th2-associated cytokine and chemokine expression profile within the skin. Restimulation of lymph node cells from OVA- and OVA/SEB-exposed mice with OVA elicited strong production of IL-13 protein, whereas substantial amounts of IFN-gamma protein were detected after SEB stimulation of cells derived from SEB- or OVA/SEB-exposed mice. Topical SEB treatment elicited vigorous production of SEB-specific IgE and IgG2a Abs and significantly increased the production of OVA-specific IgE and IgG2a Abs. The present study shows that topical exposure to SEB provokes epidermal accumulation of CD8+ T cells, a mixed Th2/Th1 type dermatitis and vigorous production of specific IgE and IgG2a Abs, which can be related to the chronic phase of atopic skin inflammation.     

Interleukin-4-mediated downregulation of cytotoxic T lymphocyte activity is associated with reduced proliferation of antigen-specific CD8+ T cells

During virus infection, exogenous IL-4 strongly downregulates expression of antiviral cytokines and cytotoxic T lymphocyte (CTL) responses. In this study, we have employed a T cell receptor (TCR) transgenic system to more closely investigate the effect of IL-4 on CTL activity. This system involves mice transgenic for an H2-Kb restricted TCR recognising an ovalbumin (OVA)-specific peptide (OT-I mice), and recombinant vaccinia viruses expressing the gene for OVA (VV-OVA), or OVA together with IL-4 (VV-OVA-IL-4). Spleen cells from OT-I mice were adoptively transferred to irradiated C57BL/6 mice infected with VV-OVA or VV-OVA-IL-4. Five days following transfer, markedly stronger CTL activity was detected in VV-OVA- than in VV-OVA-IL-4-infected recipients. The reduction in CTL activity was associated with a reduction in the number of OVA-specific CD8+ T cells. Proliferation of cells from VV-OVA-IL-4-infected recipients was dramatically reduced, and this is a likely explanation for the IL-4-mediated reduction in the total number of OVA-specific cells and the reduced cytotoxic activity. On a per cell basis, the production of IFNgamma and cytotoxic activity of OVA-specific CD8+ cells was not influenced by IL-4. Taken together, our results indicate that the reduction in CTL activity by exogenous IL-4 is due to a reduced number of antigen-specific effectors, and does not involve a downregulation of effector function of these cells.