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.     

Th cells and Th2 responses can develop in the absence of MHC class II-CD4 interactions.

In this paper, we address the question whether CD4 and MHC class II expression are necessary for the development of the T helper lineage during thymocyte maturation and for activation-induced Th2 responses. To bypass the CD4-MHC class II interaction requirements for positive selection and activation, we used mice that are doubly transgenic for CD8 and for the MHC class I-restricted TCR F5. This transgene combination leads to MHC class I-dependent maturation of CD4 lineage cells. Upon activation, these CD4 lineage T cells secrete IL-4 and give help to B cells but show no cytotoxic activity. Remarkably, neither MHC class II nor CD4 expression are necessary for the generation and helper functions of these cells. This suggests that under normal conditions, coreceptor-MHC interactions are necessary to ensure the canonical combinations of coreceptor and function in developing thymocytes, but that they do not determine functional commitment. Our results also imply that expression of the CD4 gene does not influence, but is merely associated with the decision to establish the T helper program. In addition, we show that activation through TCR-MHC class I interactions can induce Th2 responses independently of CD4 and MHC class II expression.     

Limited ability of antigen-specific Th1 responses to inhibit Th2 cell development in vivo

Th1 and Th2 cells mutually antagonize each other's differentiation. Consequently, allergen-specific Th1 cells are believed to be able to suppress the development of Th2 cells and to prevent the development of atopic disorders. To determine whether a pre-existing Ag-specific Th1 response can affect the development of Th2 cells in vivo, we used an immunization model of Ag-pulsed murine dendritic cell (DC) transfer to induce distinct Th responses. When transferred into naive mice, Ag-pulsed CD8alpha(+) DCs induced a Th1 response and the production of IgG2a, whereas CD8alpha(-) DCs primed a Th2 response and the production of IgE. In the presence of a pre-existing Ag-specific Th2 environment due to Ag-pulsed CD8alpha(-) DC transfer, CD8alpha(+) DCs failed to prime Th1 cells. In contrast, CD8alpha(-) DCs could prime a Th2 response in the presence of a pre-existing Ag-specific Th1 environment. Moreover, exogenous IL-4 abolished the Th1-inducing potential of CD8alpha(+) DCs in vitro, but the addition of IFN-gamma did not effectively inhibit the potential of CD8alpha(-) DCs to prime IL-4-producing cells. Thus, Th1 and Th2 cells differ in their potential to inhibit the development of the other. This suggests that the early induction of allergen-specific Th1 cells before allergy sensitization will not prevent the development of atopic disorders.     

New IL-17 family members promote Th1 or Th2 responses in the lung: in vivo function of the novel cytokine IL-25

We have biologically characterized two new members of the IL-17 cytokine family: IL-17F and IL-25. In contrast to conventional in vitro screening approaches, we have characterized the activity of these new molecules by direct in vivo analysis and have compared their function to that of other IL-17 family members. Intranasal administration of adenovirus expressing IL-17, IL-17C, or IL-17F resulted in bronchoalveolar lavage neutrophilia and inflammatory gene expression in the lung. In contrast, intranasal administration of IL-25-expressing adenovirus or IL-25 protein resulted in the production of IL-4, IL-5, IL-13, and eotaxin mRNA in the lung and marked eosinophilia in the bronchoalveolar lavage and lung tissue. Mice given intranasal IL-25 also developed epithelial cell hyperplasia, increased mucus secretion, and airway hyperreactivity. IL-25 gene expression was detected following Aspergillus and Nippostrongylus infection in the lung and gut, respectively. IL-25-induced eosinophilia required IL-5 and IL-13, but not IL-4 or T cells. Following IL-25 administration, the IL-5(+) staining cells were CD45R/B220(+), Thy-1(+/-), but were NK1.1-, Ly-6G(GR-1)-, CD4-, CD3-, and c-kit-negative. gamma-common knockout mice did not develop eosinophilia in response to IL-25, nor were IL-5(+) cells detected. These findings suggest the existence of a previously unrecognized cell population that may initiate Th2-like responses by responding to IL-25 in vivo. Further, these data demonstrate the heterogeneity of function within the IL-17 cytokine family and suggest that IL-25 may be an important mediator of allergic disease via production of IL-4, IL-5, IL-13, and eotaxin.     

Comparative roles of IL-4, IL-13, and IL-4Ralpha in dendritic cell maturation and CD4+ Th2 cell function

IL-4 and IL-13 play key roles in Th2 immunity and asthma pathogenesis. Although the function of these cytokines is partially linked through their shared use of IL-4Ralpha for signaling, the interplay between these cytokines in the development of memory Th2 responses is not well delineated. In this investigation, we show that both IL-4 and IL-13 influence the maturation of dendritic cells (DC) in the lung and their ability to regulate secretion of IFN-gamma and Th2 cytokines by memory CD4(+) T cells. Cocultures of wild-type T cells with pulmonary DC from allergic, cytokine-deficient mice demonstrated that IL-4 enhanced the capacity of DC to stimulate T cell secretion of Th2 cytokines, whereas IL-13 enhanced the capacity of DC to suppress T cell secretion of IFN-gamma. Because IL-4Ralpha is critical for IL-4 and IL-13 signaling, we also determined how variants of IL-4Ralpha influenced immune cell function. T cells derived from allergic mice expressing a high-affinity IL-4Ralpha variant produced higher levels of IL-5 and IL-13 compared with T cells derived from allergic mice expressing a low-affinity IL-4Ralpha variant. Although DC expressing different IL-4Ralpha variants did not differ in their capacity to influence Th2 cytokine production, they varied in their capacity to inhibit IFN-gamma production by T cells. Thus, IL-4 and IL-13 differentially regulate DC function and the way these cells regulate T cells. The affinity of IL-4Ralpha also appears to be a determinant in the balance between Th2 and IFN-gamma responses and thus the severity of allergic disease.     

IL-13 receptor alpha2 selectively inhibits IL-13-induced responses in the murine lung

IL-13 is a critical cytokine at sites of Th2 inflammation. In these locations it mediates its effects via a receptor complex, which contains IL-4Ralpha and IL-13Ralpha1. A third, high-affinity IL-13 receptor, IL-13Ralpha2, also exists. Although it was initially felt to be a decoy receptor, this has not been formally demonstrated and the role(s) of this receptor has recently become controversial. To define the role(s) of IL-13Ralpha2 in IL-13-induced pulmonary inflammation and remodeling, we compared the effects of lung-targeted transgenic IL-13 in mice with wild-type and null IL-13Ralpha2 loci. We also investigated the effect of IL-13Ralpha2 deficiency on the OVA-induced inflammatory response. In this study, we show that in the absence of IL-13Ralpha2, IL-13-induced pulmonary inflammation, mucus metaplasia, subepithelial fibrosis, and airway remodeling are significantly augmented. These changes were accompanied by increased expression and production of chemokines, proteases, mucin genes, and TGF-beta1. Similarly, an enhanced inflammatory response was observed in an OVA-induced phenotype. In contrast, disruption of IL-13Ralpha2 had no effect on the tissue effects of lung-targeted transgenic IL-4. Thus, IL-13Ralpha2 is a selective and powerful inhibitor of IL-13-induced inflammatory, remodeling, and physiologic responses in the murine lung.     

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.     

Coordinate regulation of the IL-4, IL-13, and IL-5 cytokine cluster in Th2 clones revealed by allelic expression patterns

The cytokines IL-4, IL-13, and IL-5 are markers for the Th2 subset of effector T cells and are often expressed together. These cytokine genes are organized within 140 kb of orthologous DNA in both mouse and human. Using IL-4-expressing CD4+ T cell clones derived from F1 mice, we identified allelic polymorphisms for each of these cytokines and assessed the parental identity of the cytokine mRNAs. Both monoallelic and biallelic expression occurred for each gene and for an additional gene, IL-3, that lies with GM-CSF over 450 kb telomeric on the same chromosome. When coexpressed in T cell clones, IL-4 was expressed from the same allele as IL-13 or IL-5 in 81% of instances. In contrast, there was only 52% concordance of these three cytokines at the allelic level among clones that expressed IL-3. Independent expression of the cytokine alleles occurs commonly in T cells, but the clustered locus encompassing IL-4, IL-13, and IL-5 is subject to coordinate regulation.     

Differences between IL-4- and IL-4 receptor alpha-deficient mice in chronic leishmaniasis reveal a protective role for IL-13 receptor signaling.

IL-4 receptor alpha-chain-deficient (IL-4Ralpha-/-) mice were generated by homologous and site-specific recombination, using the Cre/loxP system in BALB/c-derived embryonic stem cells. In vitro analysis of cells from these mice revealed impaired IL-4- and IL-13-mediated functions, demonstrating that the IL-4Ralpha-chain is an essential component of both the IL-4 and the IL-13 receptor. Whereas Leishmania major-infected BALB/c mice developed fatal progressive disease with type 2 Ab responses within 3 mo, both IL-4Ralpha-/- and IL-4-/- BALB/c mice contained infection with reduced footpad swelling, parasite load, moderate histopathology, and type 1 Ab responses during this time period. Conclusively, these results demonstrate an IL-4-dependent mechanism of susceptibility in BALB/c mice. Nevertheless, in contrast to mutant mice, infected C57BL/6 mice healed completely within 3 mo, indicating that additional factors are necessary for subsequent healing and elimination of the pathogen. During the further course of infection, IL-4Ralpha-/- mice developed progressive disease with massive footpad swelling. Lesions became ulcerative and necrotic with subsequent destruction of connective tissue and bones, as well as dissemination into organs and consequent mortality within the monitored 6 mo of chronic infection. In striking contrast, IL-4-/- mice maintained control of infection on a moderate level, but were unable to clear the pathogen. The distinct phenotypes of the BALB/c embryonic stem cell-derived IL-4-/- and IL-4Ralpha-/- mouse strains identify previously unsuspected mechanisms for maintaining host immunity to chronic infection with L. major, mediated by a functional IL-13 receptor.     

IL-4 inhibits IL-2-mediated induction of human lymphokine-activated killer cells, but not the generation of antigen-specific cytotoxic T lymphocytes in mixed leukocyte cultures

Human rIL-4 was studied for its capacity to induce lymphokine-activated killer (LAK) cell activity. In contrast to IL-2, IL-4 was not able to induce LAK cell activity in cell cultures derived from peripheral blood. IL-4 added simultaneously with IL-2 to such cultures suppressed IL-2-induced LAK cell activity measured against Daudi and the melanoma cell line MEWO in a dose-dependent way. IL-4 also inhibited the induction of LAK cell activity in CD2+, CD3-, CD4-, CD8- cells, suggesting that IL-4 acts directly on LAK precursor cells. IL-4 added 24 h after the addition of IL-2 failed to inhibit the generation of LAK cell activity. Cytotoxic activity of various types of NK cell clones was not affected after incubation in IL-4 for 3 days, indicating that IL-4 does not affect the activity of already committed killer cells. No significant differences were observed in the percentages of Tac+, NKH-1+ and CD16+ cells after culturing PBL in IL-2, IL-4 or combinations of IL-2 and IL-4 for 3 days. IL-4 also inhibited the activation of non-specific cytotoxic activity in MLC, as measured against K-562 and MEWO cells. In contrast, the Ag-specific CTL activity against the stimulator cells was augmented by IL-4. Collectively, these data indicate that IL-4 prevents the activation of LAK cell precursors by IL-2, but does not inhibit the generation of Ag-specific CTL.     

Enhancement of T helper2 response in the absence of interleukin (IL-)6; an inhibition of IL-4-mediated T helper2 cell differentiation by IL-6

Functional roles of interleukin (IL-)6 in T cell response were investigated. Mice deficient in IL-6 and wild mice were immunized with antigens (myelin oligodendrocyte glycoprotein or methylated BSA) and production of IL-4 and interferon (IFN)-gamma by regional lymph nodes was measured. IL-6 deficiency led to an enhancement of IL-4 and an inhibition of IFN-gamma production. Moreover, polyclonal stimulation of spleen T cells from unimmunized IL-6-deficient mice with anti-CD3 plus anti-CD28 antibodies (Abs) demonstrated an enhancement of T helper (Th)(2)responses. The presence of IL-6, however, augmented IL-4 production but it inhibited IFN-gamma expression by spleen T cells in response to polyclonal stimulation and by antigen-primed spleen T cells in response to re-challenge with the antigen. In contrast, the induction of spleen CD4-positive T cells into Th(2)cells in vitro by the anti-CD3 plus IL-4 was completely suppressed by exogenously added IL-6, whereas Th(1)differentiation of T cells by the anti-CD3 plus IL-12 was not inhibited by the presence of IL-6. Thus, these results indicate that IL-6 physiologically could modulate qualitative T cell response and suggest that it augments Th(1)responses partly through its inhibitory capability of IL-4-induced Th(2)differentiation of naive T cells.     

Lack of signaling by IL-4 or by IL-4/IL-13 has more attenuating effects on Leishmania amazonensis dorsal skin--than on footpad-infected mice

Lesion development in tegumentary leishmaniasis is markedly influenced by the inoculation site and the type and number of injected infective forms. This and the yet unclear contribution of Th2 cytokines as susceptibility factors to Leishmania amazonensis infection prompted us to investigate the roles of IL-4, IL-13 and IL-10 on C57BL/6 and BALB/c mice infected in the footpad (paw) or rump with low-dose L. amazonensis purified-metacyclics. Wild-type (WT) mice of either strain developed, in the rump, a single large ulcerated lesion whereas paw lesions never ulcerated and were much smaller in C57BL/6 than in BALB/c mice. However, rump-inoculated IL-4-deficient (IL-4(-/-)) C57BL/6 mice did not develop any visible lesions although parasites remained in the dermis and lymph nodes, even after systemic IL-10-receptor blocking. By comparison, all IL-4(-/-) BALB/c mice developed rump ulcers. Strikingly, only 30% of rump-infected IL-4Rα(-/-) BALB/c mice developed lesions. IL-4(-/-) mice had higher IFN-γ and lower IL-10 and IL-13 levels than WT mice. Paw-infected IL-4Rα(-/-) BALB/c mice developed minimal paw lesions. While other factors contributing to L. amazonensis susceptibility cannot be discounted, our results indicate that absent signalling by IL-4 or by IL-4/IL-13 have more intense attenuating effects on rump than on paw lesions but do not eradicate parasitism.     

Prostaglandin E2-EP4 signaling initiates skin immune responses by promoting migration and maturation of Langerhans cells

Antigen-specific immune responses in the skin are initiated by antigen uptake into Langerhans cells and the subsequent migration of these cells to draining lymph nodes. Although prostaglandin E2 (PGE2) is produced substantially in skin exposed to antigen, its role remains unclear. Here we show that although Langerhans cells express all four PGE receptor subtypes, their migration to regional lymph nodes was decreased only in EP4-deficient (Ptger4-/-) mice and in wild-type mice treated with an EP4 antagonist. An EP4 agonist promoted the migration of Langerhans cells, increased their expression of costimulatory molecules and enhanced their ability to stimulate T cells in the mixed lymphocyte reaction in vitro. Contact hypersensitivity to antigen was impaired in Ptger4-/- mice and in wild-type mice treated with the EP4 antagonist during sensitization. PGE2-EP4 signaling thus facilitates initiation of skin immune responses by promoting the migration and maturation of Langerhans cells.     

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.