T-cell subsets (Th1 versus Th2)

LEARNING OBJECTIVE

To understand the current status of knowledge in the basic field of polarized specific immune responses mediated by CD4+ T helper (Th) lymphocytes, based on their profile of cytokine production (type 1 or Th1 and type 2 or Th2).

DATA SOURCES

Relevant articles and publications from the medical literature, especially review articles dealing with properties, mechanisms of polarization, transcription regulatory factors, and role in different human pathophysiological conditions of Th1 and Th2 cells.

CONCLUSIONS

Th1 cells, which produce interferon (IFN)-gamma, interleukin (IL)-2 and tumor necrosis factor (TNF)-beta, evoke cell-mediated immunity and phagocyte-dependent inflammation. Th2 cells, which produce IL-4, IL-5, IL-6, IL-9, IL-10, and IL-13, evoke strong antibody responses (including those of the IgE class) and eosinophil accumulation, but inhibit several functions of phagocytic cells (phagocyte-independent inflammation). Both environmental and genetic factors act in concert to determine the Th1 or Th2 polarization. Further, Th1-dominated responses are involved in the pathogenesis of organ-specific autoimmune disorders, Crohn's disease, sarcoidosis, acute kidney allograft rejection, and some unexplained recurrent abortions. In contrast, allergen-specific Th2 responses are responsible for atopic disorders in genetically susceptible individuals. Further, Th2-dominated responses play a pathogenic role in both progressive systemic sclerosis and cryptogenic fibrosing alveolitis, and favor a more rapid evolution of HIV infection towards the full-blown disease. Finally, the Th1/Th2 paradigm can provide the basis for the development of new types of vaccines against infectious agents and of novel strategies for the therapy of allergic and autoimmune disorders.

Expression of bcl-X(L) restores cell survival, but not proliferation off effector differentiation, in CD28-deficient T lymphocytes

Lymphocytes deficient in the T cell costimulatory molecule CD28 exhibit defects in cell survival, clonal expansion, and differentiation into effector cells. It is known that CD28-mediated signaling results in the upregulation of the Bcl family member Bcl-X(L). To investigate the role that Bcl-X(L) plays in the various functions of CD28, we expressed Bcl-X(L) in CD28-deficient primary T lymphocytes using retrovirus-mediated gene transfer. T cells were activated in vitro and infected with Bcl-X(L) or control retroviruses; this method allows gene expression in activated, cycling cells. Expression of Bcl-X(L) in naive T cells was achieved by reconstitution of the immune system of lethally irradiated recipient mice with retrovirus-infected purified bone marrow stem cells from CD28(-/)- or wild-type donor mice. Our studies demonstrate that Bcl-X(L) prolongs the survival of CD28(-/)- T cells but does not restore normal proliferation or effector cell development. These results indicate that the various functions of CD28 can be dissociated, and provide an experimental approach for testing the roles of downstream signals in the functions of cellular receptors such as CD28.

Nivalenol inhibits total and antigen-specific IgE production in mice

Nivalenol (NIV) has been reported to induce hyperproduction of IgA, which is regulated by T-helper 2 cells (Th2); however, whether IgE production, which is under the regulation of Th2 cells, is induced by this compound remains largely unknown. We examined the effect of NIV on antigen-specific IgE production using ovalbumin (OVA)-specific T cell receptor alphabeta-transgenic mice. The mice produced significant amounts of total and antigen-specific IgE, IgG1, and IgA in serum when given OVA orally. Administration of NIV with OVA suppressed total IgE and OVA-specific IgE, IgG1, and IgA production significantly. Cytokine assay using splenocytes obtained from mice given the OVA plus NIV diet revealed that interleukin 4 (IL-4) production was suppressed and interleuin-2 (IL-2) production was enhanced. These results suggest that the inhibition of IL-4 production and enhancement of IL-2 production induced by NIV suppressed total and antigen-specific IgE production.

The trophoblast is a component of the innate immune system during pregnancy

Systemic infection with Listeria monocytogenes, a Gram-positive intracellular bacterium, has been used extensively to analyze the innate immune response. Macrophages are central to this response, acting as both the host for and principal defense against this bacterium. During pregnancy L. monocytogenes has a predilection for replication at the maternal-placental interface and consequently is an important cause of fetal morbidity and mortality. However, macrophages are mostly excluded from the murine placenta with neutrophils acting as the main immune effector cell against this bacterium. Colony stimulating factor (CSF)-1, a macrophage growth factor, is synthesized in high concentrations by the uterine epithelium during pregnancy, where it is targeted to trophoblast bearing CSF-1-receptors. To define the involvement of CSF-1 in placental immunity, we infected pregnant mice either homozygous or heterozygous for an inactivating recessive mutation in the gene for CSF-1 (osteopetrotic; Csfmop) with L. monocytogenes. CSF-1 was required to recruit neutrophils to the site of listerial infection in the decidua basalis, and infection by Listeria remained unrestrained in its absence. CSF-1 acted by inducing the trophoblast to synthesize the neutrophil chemoattractants (KC) and macrophage inflammatory protein (MIP)-2. Thus, during pregnancy, trophoblast responsive to CSF-1 acts to organize the maternal immune response to bacterial infection at the utero-placental interface. This previously unknown function indicates that the trophoblast acts as a pregnancy-specific component of the innate immune system.

Beclomethasone decreases elevations in phosphodiesterase activity in human T lymphocytes

BACKGROUND

We recently reported that CD4+ T cells that have been activated in vivo or in vitro contain elevated cyclic adenosine monophosphate (cAMP) phosphodiesterase (PDE) activity. Since both phosphodiesterase inhibitors and glucocorticoids have anti-inflammatory activity, we sought to investigate the effect of beclomethasone on PDE activity.

METHODS

PDE activity was measured in CD4+ T cells after 24 h of culture with beclomethasone. Cells were obtained from the peripheral blood of nonatopic persons (nCells), pre-seasonal (pCells), seasonal (within the first 2 weeks; sCells) and mid-seasonal (mCells) allergic rhinitics and asymptomatic allergic asthmatics (aCells). In addition, the effect of beclomethasone on Th2 cell lines and cells that had been activated in vitro with PHA or interleukin (IL)-2 was determined.

RESULTS

PDE activity was decreased in a concentration-dependent manner by incubation of mCells, Th2 lines and PHA or IL-2-activated CD4+ T cells with beclomethasone (p < 0.05). However, beclomethasone did not modulate PDE activity in nCells, pCells, sCells, or aCells.

CONCLUSIONS

Beclomethasone only decreases cAMP PDE activity in CD4+ T cells when it is increased by cell activation either in vitro or in vivo.

IL-15 promotes survival but not effector function differentiation of CD8+ TCRalphabeta+ intestinal intraepithelial lymphocytes

CD8 single-positive cells, including CD8alphaalpha+ and CD8alphabeta+ subsets, constitute the majority of TCRalphabeta+ intestinal intraepithelial lymphocytes (alphabeta iIEL) in mice. CD8+ alphabeta iIEL show significantly weaker responses to TCR stimulation in the presence of exogenous IL-2 than do CD8+ T cells of the central immune system. IL-15 is a T cell growth factor likely expressed in the intestine mucosa. To understand the role of IL-15 in CD8+ alphabeta iIEL biology, we compared the effects of exogenous IL-15 and IL-2 on the survival and primary responses of the two CD8+ alphabeta iIEL subsets in vitro. In contrast to the death of approximately 60% of both CD8alphaalpha+ and CD8alphabeta+ iIEL cultured in IL-2 with or without TCR stimulation, IL-15 promoted survival of the CD8alphaalpha+ subset in the presence of TCR stimulation and promoted survival of both subsets in the absence of TCR stimulation. The higher proliferation level of TCR stimulated CD8alphaalpha+ alphabeta iIEL cultured in IL-15 compared with those cultured in IL-2 is likely due to IL-15's prosurvival effects. In addition, unlike exogenous IL-2, exogenous IL-15 did not support the effector functions of either iIEL subsets, including IFN-gamma production, IL-4-induced Th2 cytokine production, and anti-TCR mAb-redirected cytotoxicity. These findings demonstrate that IL-15 and IL-2 are functionally distinct and suggest that IL-15 plays a unique role in the maintenance of the CD8+ alphabeta iIEL pool in the absence of Ag stimulation and in the survival and expansion of CD8alphaalpha+ alphabeta iIEL upon Ag stimulation.

Essential role for both CD80 and CD86 costimulation, but not CD40 interactions, in allergen-induced Th2 cytokine production from asthmatic bronchial tissue: role for alphabeta, but not gammadelta, T cells

CD80 and CD86 interact with CD28 and deliver costimulatory signals required for T cell activation. We demonstrate that ex vivo allergen stimulation of bronchial biopsy tissue from mild atopic asthmatic, but not atopic nonasthmatic, subjects induced production of IL-5, IL-4, and IL-13. Explants from both study groups did not produce IFN-gamma, but secreted the chemokine RANTES without any overt stimulation. In addition to allergen, stimulation of asthmatic explants with mAbs to CD3 and TCR-alphabeta but not TCR-gammadelta induced IL-5 secretion. Allergen-induced IL-5 and IL-13 production by the asthmatic tissue was inhibited by anti-CD80 and, to a lesser extent, by anti-CD86 mAbs. In contrast, the production of these cytokines by PBMCs was not affected by mAbs to CD80, was inhibited by anti-CD86, and was strongly attenuated in the presence of both Abs. FACS analysis revealed that stimulated asthmatic bronchial tissue was comprised of CD4+ T cells that expressed surface CD28 (75. 3%) but little CTLA-4 (4.0%). Neutralizing mAbs to CD40 ligand had no effect on the cytokine levels produced by asthmatic tissue or PBMCs. Collectively, these findings suggest that allergen-specific alphabeta T cells are resident in asthmatic bronchial tissue and demonstrate that costimulation by both CD80 and CD86 is essential for allergen-induced cytokine production. In contrast, CD86 appears to be the principal costimulatory molecule required in PBMC responses. Attenuation of type 2 alphabeta T cell responses in the bronchial mucosa by blocking these costimulatory molecules may be of therapeutic potential in asthma.

The preventive effects of incomplete Freund's adjuvant and other vehicles on the development of adjuvant-induced arthritis in Lewis rats

The present study showed a novel finding that the development of adjuvant-induced arthritis (AA) in Lewis rats was completely prevented by incomplete Freund's adjuvant (IFA) injected 21 or 28 days before complete Freund's adjuvant (CFA) challenge. Hexadecane also completely prevented AA and squalane, methyl oleate and pristane moderately prevented AA, though pristane by itself induced mild arthritis in two out of five rats. Concanavalin A-stimulated lymph node cells (LNCs) isolated from AA rats were able to adoptively transfer the severe polyarthritis to all the naive recipients or even to the IFA pretreated recipients with earlier onset and more rapid progression than those of AA. The LNCs from the donors who had been pretreated with IFA and subsequently challenged with CFA could induce mild arthritis in only two out of eight naive recipients, whereas all the recipients who were challenged with CFA immediately after intravenous injection of these LNCs developed significantly less severe arthritis. However, the LNCs from IFA-pretreated donors failed to prevent AA. According to the T helper type 1 (Th1)/Th2 paradigm, it was suggested that the adjuvant-active vehicles such as IFA, hexadecane, squalane, methyl oleate and pristane, can affect and deviate the Th1/Th2 balance of immune responses in host. CFA could promote the propagation of Th2 cells rather than Th1 cells in these vehicle-pretreated rats through as yet undetermined mechanisms, eventually resulting in the prevention of AA. Finally, we discussed a regulatory role of adjuvant vehicles for induction and suppression of AA.

Nonpathogenic common variants of IFNGR1 and IFNGR2 in association with total serum IgE levels

Atopy is an immune disorder in which a Th2 dominant mechanism leads to high IgE levels and the clinical disorder asthma. It has been postulated that the Th1 cytokine IFNgamma, acting through its heterodimeric receptors, IFNgammaR1 and IFNgammaR2, in the induction/proliferation of Th1 cells, might suppress the Th2 responses that may underlie atopic asthma. However, neither murine nor human variants of IFNgamma associate with atopy. Several dysfunctional mutations have been identified in IFNgamma receptor genes (IFNGR1 and IFNGR2) in relation to severe and selective infections with poorly pathogenic organisms. However, little is known about common polymorphisms and their functional role in atopy. To test whether such variants of IFNGR1 and IFNGR2 relate to atopic asthma, we conducted a genetic association study in both British (n = 300) and Japanese (n = 200) populations. An intronic variant of IFNGR1 showed marginal association with total serum IgE levels in the British population compared with those with total IgE levels <30 IU/ml and those with >120-500 IU/ml [odds ratio = 2.00 (95% CI 1. 00-4.07), P = 0.048]. A coding variant, Gln64Arg of the IFNGR2, also associated with total serum IgE levels in the British population [chi(2) = 5.08, P = 0.024]. Further genetic and functional analyses are needed to clarify the role of variants of IFNgamma receptor genes in atopic immune disorder among different ethnic groups.

Schistosoma mansoni: IL-4 is necessary for concomitant immunity in mice

To ask whether type-2 immune responses serve an essential role in concomitant immunity, that is the prevention of superinfection with Schistosoma mansoni, we compared resistance to a challenge infection in infected wild-type (WT) mice and in infected IL-4-/- mice, which are unable to mount Th2 responses during schistosomiasis. Although WT mice are protected from superinfection, resistance is abrogated in the absence of interleukin (IL)-4. We conclude that IL-4 or IL-4-dependent responses, or both, are necessary for resistance to S. mansoni superinfection in mice.

Interleukin (IL)-4, IL-10 and IL-12 profile in serum of patients with alveolar echinococcosis

Alveolar echinococcosis (AE), caused by Echinococcus multilocularis (E.m.), provokes a characteristic immune response. Based mainly on in vitro studies, Th2 dominated immunity is associated with increased susceptibility to disease, while Th1 cell activation is assumed to induce protective immunity. We investigated serum levels of interleukin (IL)4, IL-10, and IL-12 in 40 AE patients and 20 controls to assess Th1/Th2 cell activation in vivo. Significantly higher levels of IL-10 were found in AE patients (P = 0.003) than in controls, with a tendency to higher concentrations in progressive cases. In contrast, IL-4 was only measurable in a minority of patients and controls. IL-12 levels (measured with an ELISA that detects both the p35/p40 heterodimer and free p40) were comparable between AE patients and controls and showed a similar distribution pattern to IL-10 with regard to disease progression. By using an IL-12-ELISA specific for the heterodimer, only minute amounts of IL-12 were detectable in merely a minority of samples. In conclusion, our data are suggestive of Th2 dominated immune response in AE in vivo.

Chemokines and chemokine receptors: role in HIV infection

Our understanding of the host factors that determine susceptibility and progression of HIV infection has been very limited. In particular, it has been not clear why some people remain uninfected being repeatedly exposed to HIV-1, and others who have been infected by HIV, remain clinically asymptomatic for long periods of time. Recently it has been demonstrated that mutated forms of a number of chemokine receptors that act as coreceptors for HIV-1 entry may account for some of these phenomena. Furthermore, chemokines such as RANTES and others, being the natural ligands for chemokine receptors, have been shown to be effective inhibitors of HIV-1 infection. In this review we discuss some of the genetic, immunological, virological and epidemiological data relevant to the very important role chemokines and chemokine receptors play in HIV pathogenesis with special reference to the increased susceptibility of the African host to HIV infection.

[Th1-Th2 cytokine correlates (INF-gamma and IL-4) in splenectomized patients]

This paper attempts to explain if immunodepression in patients who had undergone a splenectomy may be due to altered balance between Th1-Th2 lymphocyte subpopulations, as shown in several studies on phagocyte and lymphocyte cells. This was achieved by dosing serum levels of IFNg, produced by Th1 lymphocytes and IL-4, produced by Th2 lymphocytes. Final analysis showed immunodepression in splenectomized patients but also emphasized that in 70% of all cases, there is functional damage of T-lymphocytes that continues for several years after the surgery involving both cellular and humoral immunity. Immunoglobulin dosage allows the increase of IgE to be seen in 50% of the splenectomized patients studied, all with allergic symptoms that appeared after the operation. The production of IgE is stimulated by Th2 lymphocytes. This leaves one to believe that splenectomy may favour the persistence of allergens in the blood, the appearance of allergic symptoms and the increase of IgE serum levels in patients with normal Th2 functioning and consequently, with normal or increased IL-4 serum levels.

Pooled human immunoglobulin inhibits IL-4 but not IFN-gamma or TNF-alpha secretion following in vitro stimulation of mononuclear cells with Staphylococcal superantigen

Intravenous immunoglobulin preparations have been successfully used in many disorders, where immunomodulation rather than immunoglobulin replacement has been the goal of therapy. The exact mechanisms by which immunoglobulin exerts its immunomodulatory effects are unclear. Proposed mechanisms include modification of T cell activation and alteration to cytokine production. As intravenous immunoglobulin therapy has been used in a number of disorders where superantigens are proposed to play a role in the disease pathogenesis, we have examined the effect of in vitro human pooled immunoglobulin on cytokine production from peripheral blood mononuclear cells in response to activation with the Staphylococcal superantigen Staphylococcal enterotoxin B. The authors found inhibition of secretion of interleukin 4 (IL-4) (P<0.001) but not interferon gamma (IFN-gamma) (P=0.13) or tumour necrosis factor alpha (TNF-alpha) (P=0.66) by pooled immunoglobulin at concentrations (6 g/l) which approximate the rise in serum immunoglobulin following in vivo IVIG therapy. Mononuclear cell proliferation was also inhibited by addition of pooled immunoglobulin to superantigen stimulated cultures. These effects do not relate to specific anti-staphylococcal enterotoxin B antibodies in the immunoglobulin preparation. The authors show that pooled human immunoglobulin can differentially modulate the secretion of IL-4 and IFN-gamma in response to superantigen stimulation.

Formation of multinucleated giant cells in the mouse lung is promoted in the absence of interleukin-12

The formation of multinucleated giant cells (MGCs) in an in vivo model of pulmonary inflammation was investigated to determine whether these cells are the result of a dominant T helper (Th) 1 or Th2 cytokine environment. We report that knockout (KO) mice with a disrupted interleukin (IL)-12 p40 gene exposed to the helminth Schistosoma mansoni had abundant and very large MGCs (> 50 microm) in their lungs concurrent with extensive eosinophilia and a population of large macrophages. Many of the MGCs and macrophages appeared to have phagocytosed eosinophils as part of a clearance process. The KO mice also had a strongly polarized Th2 immune response as judged by elevated levels in the lungs of messenger RNA (mRNA) transcripts for IL-4, IL-5, IL-6, and IL-13, but decreased levels of mRNA for interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha). In addition, cells recovered by bronchoalveolar lavage from the airways of these mice secreted a Th2-biased profile of cytokines upon restimulation in vitro with parasite antigen. In contrast, wild-type C57BL/6 or KO mice treated with recombinant IL-12 had a polarized Th1 phenotype with elevated levels of IFN-gamma and TNF-alpha mRNA in the lungs, and an airway cell population that secreted abundant IFN-gamma. Very few MGCs were detected in these mice, and there was an absence of pulmonary eosinophilia. We conclude that the formation of MGCs in our model is promoted in the absence of IL-12 and is linked instead to the abundance of Th2 cytokines, notably IL-4 and IL-13.

Immunological and endocrinological characteristics of tuberculosis that provide opportunities for immunotherapeutic intervention

Immunity to tuberculosis requires a T helper 1 (Th1) response which can be compromised by excessive release of inflammatory cytokines or Th2 activity. Environmental saprophytes can protect against tuberculosis by inducing Th1 recognition of the common antigens, or make mice more susceptible to tuberculosis than unimmunized controls by evoking a Th2 response. A mixed Th1 + Th2 response increases the local toxicity of tumour necrosis factor alpha (TNF-alpha). Some saprophytes are potent immunogens. A killed preparation of Mycobacterium vaccae can cause systemic activation of spontaneously Th1 cytokine-secreting cells in humans, and can non-specifically suppress pre-existing IgE formation and interleukin 5 (IL-5) production in murine models of allergy. These effects, and the Th2-inducing effects of other species, may explain the variable efficacy of Bacillus Calmette-Guérin, and suggest the need for new approaches to the screening of vaccines before trial in humans. The balance of Th1 to Th2 and the function of inflammatory cytokines are also regulated by cortisol. Glucocorticoid metabolism is abnormal in tuberculosis, suggesting overactivity of 11-beta-hydroxysteroid reductase enzymes. The reductase activity of these enzymes is enhanced by TNF-alpha and IL-1 beta. The roles of Th2, inflammatory cytokines, common antigens and changes in cortisol metabolism suggest several strategies for immunotherapy, and several sites where genetic polymorphisms may affect susceptibility.

[Flow cytometric analysis of helper T cell subsets (Th1 and Th2) in healthy adults]

To estimate frequency of T helper (Th) 1, Th2, and other related subsets in T cells among healthy Japanese, we determined the frequencies of interferon (IFN)-gamma- and/or interleukin (IL)-4-producing cells in stimulated peripheral blood lymphocytes (PBL) from 51 healthy adults of various ages by three-color flow cytometry using FITC-labeled anti-IFN-gamma, PE-conjugated anti-IL-4, and peridinin chlorophyll protein (PerCP)-labeled anti-CD4 or anti-CD3 antibody. As a result, proportions (mean +/- SD) of IFN-gamma-single positive (conveniently called Th1), IL-4-single positive (Th2), and double-positive cells (Th0) in CD4+ PBL, and homologous cell populations in CD3+ PBL (Th1 type, Th2 type, and Th0 type cells) were 21.3 +/- 8.2%, 2.7 +/- 1.1%, 1.9 +/- 1.0%, 39.5 +/- 13.5%, 1.7 +/- 0.8%, and 1.8 +/- 1.0%, respectively. Percentages of Th1 and Th2 were roughly consistent with those reported previously. Proportions of Th1, Th2, Th1 type, and Th2 type cells were found to increase with the age, whereas there were no significant difference in sex at least in 20s. Furthermore, positive correlation was seen between Th1 and Th1 type (r = 0.79), Th2 and Th2 type (r = 0.87), and Th0 and Th0 type (r = 0.86). Frequencies of these subsets in each donor were maintained at substantially the same levels for at least 3 months, suggesting existence of particular and stable Th1/Th2 balance among healthy individuals. As reported, 6 patients with atopic dermatitis examined in this study showed significantly lower frequencies of Th1 (11.0 +/- 2.5%) as compared with healthy donors (p < 0.01), implying usefulness of the immune test.

Mycobacterial dose defines the Th1/Th2 nature of the immune response independently of whether immunization is administered by the intravenous, subcutaneous, or intradermal route

It is believed that cell-mediated immunity alone can contain Mycobacterium tuberculosis, the pathogen responsible for tuberculosis. The induction of antibody, or of a mixed cell-mediated/humoral response, is associated with tuberculous disease. It is therefore important to determine the conditions of immunization with bacille Calmette Guérin (BCG), the attenuated strain of Mycobacterium bovis used to vaccinate humans against tuberculosis, that optimally induces an exclusive cell-mediated, Th1 response. Such a determination will then allow an assessment of whether the generation of such an exclusive Th1 response results in the generation of a Th1 imprint against mycobacteria. This Th1 imprint would ensure that the Th1 response is predominant following any challenge. We therefore tested the proposition that the dose of mycobacteria used for immunization generally determines the Th1/Th2 nature of the ensuing response. Our results demonstrate that relatively low doses lead to an almost exclusive cell-mediated, Th1 response, while higher doses induce a mixed Th1/Th2 response. Furthermore, the dependence on dose is independent of whether BCG is administered intravenously, subcutaneously, or intradermally. The implications of our findings to understanding how different classes of immunity are induced, to the epidemiology of tuberculosis, and to the design of effective vaccination strategies are discussed.

The pro-allergic influences of helminth parasites

Parasitic infection is highly allergenic, and the present paper illustrates how parasites might disrupt the regulation of IgE synthesis, resulting in heightened Th-2 responses. The study of parasites, and dysregulation of the IgE network, could in turn provide information relating to the aetiology of allergic diseases such as asthma and atopic dermatitis.

The debate over the effector function of eosinophils in helminth infection: new evidence from studies on the regulation of vaccine immunity by IL-12

The production of Th1-type cytokines is associated with strong cell-mediated immunity while Th2-type cytokines are typically involved in the generation of humoral immune responses. In mice vaccinated a single time (1X) with attenuated cercariae of Schistosoma mansoni, the immunity induced is highly dependent on CD4+ T cells and IFN-gamma. In contrast, mice vaccinated multiple times (3X) have decreased IFN-gamma expression, develop a more dominant Th2-type cytokine response as well as protective antibodies which can passively transfer immunity to naive recipients. Previously, we demonstrated the ability of IL-12, a potent IFN-gamma-inducing cytokine to enhance (1X) schistosome cell-mediated saline-treated mice demonstrated a 70 immunity when administered during the period of immunization. More recently, we asked what effects IL-12 would have on the development humoral-based immunity. While multiply-immunized/ saline-treated mice demonstrated a 70-80% reduction in parasite burden, 3X/IL-12-vaccinated animals displayed an even more striking > 90% reduction in challenge infection, with many mice in the later group demonstrating complete protection. Analysis of pulmonary cytokine mRNA responses demonstrated that control challenged mice elicited a dominant Th2-type response, 3X/saline-vaccinated produced a mixed Th1/Th2-type cytokine response, while 3X/IL-12-immunized animals displayed a dominant Th1-type response. The IL-12-treated group also showed a marked reduction in total serum IgE and tissue eosinophilia while SWAP-specific IgG2a and IgG2b Abs were elevated. Interestingly, animals vaccinated with IL-12 also showed a highly significant increase in total Ig titers specific for IrV, a known protective antigen. More importantly, 3X/IL-12 serum transferred significantly less protection. Nevertheless, animals vaccinated in the presence of IL-12 also develop macrophages with enhanced nitric oxide dependent killing activity against the parasites. Together, these observation suggest that IL-12, initially described as an adjuvant for cell-mediated immunity, may also be used as an adjuvant for promoting both humoral and cell-mediated protective responses.

IL-5 and IL-5 receptor in asthma

Eosinophils, along with mast cells are key cells involved in the innate immune response against parasitic infection whereas the adaptive immune response is largely dependent on lymphocytes. In chronic parasitic disease and in chronic allergic disease, IL-5 is predominantly a T cell derived cytokine which is particularly important for the terminal differentiation, activation and survival of committed eosinophil precursors. The human IL-5 gene is located on chromosome 5 in a gene cluster that contains the evolutionary related IL-4 family of cytokine genes. The human IL-5 receptor complex is a heterodimer consisting of a unique alpha subunit (predominantly expressed on eosinophils) and a beta subunit which is shared between the receptors for IL-3 & GM-CSF (more widely expressed). The alpha subunit is required for ligand-specific binding whereas association with the beta subunit results in increased binding affinity. The alternative splicing of the alpha IL-5R gene which contains 14 exons can yield several alpha-IL-5R isoforms including a membrane-anchored isoform (alpha IL-5Rm) and a soluble isoform (alpha IL-5Rs). Cytokines such as IL-5 produce specific and non-specific cellular responses through specific cell membrane receptor mediated activation of intracellular signal transduction pathways which, to a large part, regulate gene expression. The major intracellular signal transduction mechanism is activation of non-receptor associated tyrosine kinases including JAK and MAP kinases which can then transduce signals via a novel family of transcriptional factors named signal transducers and activators of transcription (STATS). JAK2, STAT1, and STAT5 appear to be particularly important in IL-5 mediated eosinophil responses. Asthma is characterized by episodic airways obstruction, increased bronchial responsiveness, and airway inflammation. Several studies have shown an association between the number of activated T cells and eosinophils in the airways and abnormalities in FEV1, airway reactivity and clinical severity in asthma. It has now been well documented that IL-5 is highly expressed in the bronchial mucosa of atopic and intrinsic asthmatics and that the increased IL-5 mRNA present in airway tissues is predominantly T cell derived. Immunocytochemical staining of bronchial biopsy sections has confirmed that IL-5 mRNA transcripts are translated into protein in asthmatic subjects. Furthermore, the number of activated CD4 + T cells and IL-5 mRNA positive cells are increased in asthmatic airways following antigen challenge and studies that have examined IL-5 expression in asthmatic subjects before and after steroids have shown significantly decreased expression following oral corticosteroid treatment in steroid-sensitive asthma but not in steroid resistant and chronic severe steroid dependent asthma. The link between T cell derived IL-5 and eosinophil activation in asthmatic airways is further strengthened by the demonstration that there is an increased number of alpha IL-5R mRNA positive cells in the bronchial biopsies of atopic and non-atopic asthmatic subjects and that the eosinophil is the predominant site of this increased alpha IL-5R mRNA expression. We have also shown that the subset of activated eosinophils that expressed mRNA for membrane bound alpha IL-5r inversely correlated with FEV1, whereas the subset of activated eosinophils that expressed mRNA for soluble alpha IL-5r directly correlated with FEV1. Hence, not only does this data suggest that the presence of eosinophils expressing alpha IL-5R mRNA contribute towards the pathogenesis of bronchial asthma, but also that the eosinophil phenotype with respect to alpha IL-5R isoform expression is of central importance. Finally, there are several animal, and more recently in vitro lung explant, models of allergen induced eosinophilia, late airway responses (LARS), and bronchial hyperresponsiveness (BHR)--all of which support a link between IL-5 and airway eosinophilia and bronc

HIV-1 envelope protein gp120 triggers a Th2 response in mice that shifts to Th1 in the presence of human growth hormone

Immunization of mice with HIV-1-gp120 results in predominant activation of the Th2 lymphocyte subset, leading to enhanced IL-4 production. Administration of human growth hormone at the time of gp120 immunization provokes a change in the cytokine production pattern, with lower IL-4 and higher gamma-IFN and IL-2 synthesis levels, indicating a preferential switch in stimulation from Th2 to Th1 cells. A growth hormone would thus be of great use for pharmacological intervention in those cases in which an infectious microorganism evades immune defenses by provoking a Th2 response. In addition, the ability of growth hormone to induce a Th1-type response upon vaccination with an HIV-antigen should be examined in the development of new therapeutic strategies or in the design of novel vaccines against HIV infection.

Human IP-10 selectively promotes dominance of polyclonally activated and environmental antigen-driven IFN-gamma over IL-4 responses

Human interferon-inducible protein 10 (IP-10) differs from most chemokines in its apparent specificity for activated T lymphocytes. We hypothesized that IP-10 was relevant not only for recruiting T cells to inflammatory sites, but also for regulating cytokine synthesis patterns. We examined the effect of recombinant human IP-10 (rhIP-10) on human interferon gamma (IFN-gamma) and interleukin 4 (IL-4) production by fresh peripheral blood mononuclear cells. We demonstrate for the first time that this CXC chemokine selectively up-regulates human T cell cytokine synthesis, with enhancement selectively targeted to promotion of Th1-like dominance. Superantigen (TSST-1), soluble anti-CD3 mAb, and phytohemagglutinin were used to activate distinct intracellular signaling pathways, thereby inducing quantitatively different IFN-gamma:IL-4 ratios. Selective enhancement of IFN-gamma responses was consistently observed, with median increases of 105-470%. Environmental antigens (Ag) were used to evaluate IP-10's effect on CD4-dependent, chloroquine-sensitive cytokine synthesis. Ag-driven IFN-gamma responses exhibited median 19- to 30-fold increases in the presence of nanomolar concentrations of rhIP-10. IL-4 responses were neither enhanced nor inhibited under any of the conditions tested. These findings suggest a potential role for this T cell-focused chemokine in maintenance of the default Th1-like responses usually seen to environmental Ag and indicate a potential application in the modulation of Ag-driven responses in vivo.

Combination immunotherapy and antifungal chemotherapy

Historical clinical observations suggested that cellular immunity is central in the outcome of deep fungal infections, and experimental observations later proved this. Unstimulated effector cells interact synergistically with antifungal drugs. Recombinant cytokines, of which interferon gamma (IFN-gamma) is the most prominent, stimulate several host-effector cells (macrophages, monocytes, neutrophils) for antifungal activity. Effector cells stimulated by such molecules (data with macrophage colony-stimulating factor, granulocyte colony-stimulating factor, and granulocyte-macrophage colony-stimulating factor with azoles are presented as examples) also have enhanced synergistic activity with antifungals. A tilt toward a type 1 T-helper (Th1) cell pathway seems essential in antifungal host defenses. Cytokines (and anticytokines) that promote this pathway can be protective in vivo and act cooperatively with antifungal drugs. Observations with interleukin (IL)-12, IFN-gamma, and anti-IL4 illustrate this. The clinical applications of these strategies are just beginning.

T helper 1 (Th1) and Th2 characteristics start to develop during T cell priming and are associated with an immediate ability to induce immunoglobulin class switching

The respective production of specific immunoglobulin (Ig)G2a or IgG1 within 5 d of primary immunization with Swiss type mouse mammary tumor virus [MMTV(SW)] or haptenated protein provides a model for the development of T helper 1 (Th1) and Th2 responses. The antibody-producing cells arise from cognate T cell B cell interaction, revealed by the respective induction of Cgamma2a and Cgamma1 switch transcript production, on the third day after immunization. T cell proliferation and upregulation of mRNA for interferon gamma in response to MMTV(SW) and interleukin 4 in response to haptenated protein also starts during this day. It follows that there is minimal delay in these responses between T cell priming and the onset of cognate interaction between T and B cells leading to class switching and exponential growth. The Th1 or Th2 profile is at least partially established at the time of the first cognate T cell interaction with B cells in the T zone. The addition of killed Bordetella pertussis to the hapten-protein induces nonhapten-specific IgG2a and IgG1 plasma cells, whereas the anti-hapten response continues to be IgG1 dominated. This indicates that a Th2 response to hapten-protein can proceed in a node where there is substantial Th1 activity.

Anti-tumor immunity induced by murine melanoma cells transduced with the Mycobacterium tuberculosis gene encoding the 38-kDa antigen

The Mycobacterium tuberculosis Ag38 gene, which encodes a highly immunogenic protein, was cloned into a retroviral vector in-frame with the leader and the transmembrane portion of the nerve growth factor receptor, and transduced into murine melanoma cell line B16-B78. Significant protection was observed in mice immunized with the transduced melanoma cells and subcutaneously challenged with parental melanoma cells since only 20% of mice developed tumors. Necroscopy of mice immunized with the transduced melanoma cells revealed dramatic inhibition of experimental metastases induced by intravenous (i.v.) inoculation of parental melanoma cells. Moreover, vaccination with transduced cells significantly prolonged survival of mice challenged i.v. with parental melanoma cells. These data indicate that the presence of the mycobacterial 38-kDa protein greatly enhances immunological recognition of structures expressed by the parental melanoma cells. Comparison of Th1 and Th2 responses in mice immunized with parental melanoma cells versus mice receiving the transduced cells revealed a clear predominance of Th1 responses when the Ag38 protein was endogenously expressed. This transduction approach may represent a promising immunotherapeutic strategy for the treatment of cancer patients.

Profile of cytokine mRNA expression in peri-implantation human endometrium

The human embryo and subsequent fetus is a semi-allograft and immunologically foreign to the mother. Successful embryonic implantation and maintenance of normal pregnancy depends on intricate interactions between the invading embryo, maternal endometrium and maternal immune response. Cytokines are pivotal in determining the type of maternal T-helper immune response, which can be divided into T-helper 1 (TH1)-mediated delayed hypersensitivity and T-helper 2 (TH2)-mediated humoral immunity. We examined the pattern of TH1 [interleukin (IL)-2, IL-12 and interferon-gamma] and TH2 (IL-4 and IL-6) cytokine expression in the peri-implantation endometrium of 10 fertile, multiparous women. Endometrial samples were timed to the mid-cycle luteinizing hormone (LH) surge, with collection on days LH+7 to LH+9. Analysis for cytokine mRNA was by mRNA extraction and reverse transcription-polymerase chain reaction. The results show a lack of TH1 and predominant TH2 cytokine expression. We postulate that endometrial cytokines may contribute to the local modulation of maternal adaptive immune response in peri-implantation endometrium, to facilitate successful embryonic implantation and maintenance of pregnancy.

Cytokines as determinants of disease and disease interactions

The immune response to pathogens results in both host resistance and immunopathology. Cytokines and in particular those lymphokines produced by Th1 and Th2 cells play a key role in determining the balance between these two immunologic outcomes. Recent data suggest that interleukin-10, a product of both Th2 cells and macrophages, protects the host against excessive immunopathology. The cytokine environment generated by different pathogens may also influence the course and outcome of infections with unrelated organisms. This relationship may be particularly important in the case of HIV-1 where prior Th1 or Th2 biases established by helminth or intracellular infections may influence either initial viral susceptibility or drive progression to AIDS through immune activation.

CD3-CD4+ cells with a Th2-like pattern of cytokine production in the peripheral blood of a patient with cutaneous T cell lymphoma

A case of cutaneous T cell lymphoma associated with mild eosinophilia and rise of IgE levels is reported. A population of CD3-CD4+ cells was observed in the peripheral blood. After activation, these purified CD3-CD4+ cells showed a Th2 pattern of cytokine production, secreting higher levels of IL-5 and IL-4 and lower levels of IFN-gamma compared to the patient's and controls' CD3+CD4+ cells. Moreover, high levels of IL-5 and soluble CD30, a marker of Th2 cell activation, were detected in the patient's serum.

T-helper 2 involvement in the pathogenesis of bullous pemphigoid: role of soluble CD30 (sCD30)

Bullous pemphigoid (BP) is an autoimmune blistering skin disease in which autoantibodies are directed against hemidesmosomal proteins of basal keratinocytes. The presence of activated T helper cells in lesions and peripheral blood of BP patients, the eosinophilia, the high levels of serum IgE, eosinophil cationic protein and soluble immune products such as IL-2, sIL-2R, IL-5, soluble CD23 (sCD23) strongly suggest the involvement of a cell-mediated immune reaction in which Th2 lymphocytes could play a pivotal role. To seek evidence to support this hypothesis we evaluated serum levels of IL-4 and sCD30, a specific activation marker of cells able to produce Th2-like cytokines, in 25 patients affected with BP. Serum from both healthy donors and pemphigus vulgaris (PV) patients were used as controls. Our results demonstrated significantly higher levels of IL-4 and sCD30 in patients with BP in relation to both normal individuals (16.6 +/- 7.9 vs 4.5 +/- 2.2 pg/ml, P < 0.0001; 30.3 +/- 10 vs 10.5 +/- 4 U/ml, P < 0.0001) and PV patients (6.2 +/- 4 pg/ml, P < 0.0001; 16 +/- 8.5 U/ml, P < 0.0001). Furthermore, a positive correlation between IL-4 and sCD30 was found (R = 0.85, P < 0.0001). In a subset of seven patients observed after systematic immunosuppressive therapy, we detected a significant reduction in sCD30 serum level (36.9 +/- 7.3 vs 16.3 +/- 6.8 U/ml, P = 0.002), with a parallel improvement in their clinical condition. These results seem to be consistent with the systematic involvement of Th2 lymphocytes in the pathogenesis of BP and suggest a role for sCD30 as a serological marker of disease activity.

An interleukin 4 (IL-4)-independent pathway for CD4+ T cell IL-4 production is revealed in IL-4 receptor-deficient mice

IL-4 receptor alpha chain (IL-4Ralpha)-deficient mice were generated by gene-targeting in BALB/c embryonic stem cells. Mutant mice showed a loss of IL-4 signal transduction and functional activity. The lack of IL-4Ralpha resulted in markedly diminished, but not absent, TH2 responses after infection with the helminthic parasite Nippostrongylus brasiliensis. CD4+, CD62L-high, and CD62L-low T cell populations from uninfected IL-4Ralpha-/- mice were isolated by cell sorting. Upon primary stimulation by T cell receptor cross-linkage, the CD62L-low, but not the CD62L-high, cells secreted considerable amounts of IL-4, which was strikingly enhanced upon 4-day culture with anti-CD3 in the presence or absence of IL-4. CD62L-low cells isolated from IL-4Ralpha-/-, beta2-microglobulin-/- double homozygous mice produced less IL-4 than did either IL-4Ralpha-/- or wild-type mice. These results indicate that an IL-4-independent, beta2-microglobulin-dependent pathway exists through which the CD62L-low CD4+ population has acquired IL-4-producing capacity in vivo, strongly suggesting that these cells are NK T cells.

Interferon-gamma and interleukin-4 regulate T cell interleukin-12 responsiveness through the differential modulation of high-affinity interleukin-12 receptor expression

Interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) are mutually antagonistic cytokines that stimulate CD4+ T cells to develop into either Th1 or Th2 cells. One feature of Th2 differentiation in mice is the loss of IL-12-induced Jak2 and Stat4 activation, which is accompanied by the inability to produce IFN-gamma in response to IL-12. In this report, we show that freshly isolated human T cells activated with phytohemagglutinin (PHA) in the presence of IL-4 exhibit a greatly diminished response to IL-12, whereas the IL-12 response of T cells activated with PHA plus IFN-gamma is enhanced. Radiolabeled IL-12 binding studies demonstrate that the impairment of T cell IL-12 responsiveness by IL-4 is associated with the down-regulation of high-affinity IL-12 receptor expression. In contrast, the enhancement of IL-12 responsiveness by IFN-gamma is associated with the upregulation of high-affinity IL-12 receptor expression. Through the use of a newly synthesized neutralizing antibody to the low-affinity IL-12 receptor beta subunit (IL-12Rbeta), we show that neither IL-4 nor IFN-gamma affect the expression of IL-12Rbeta, which we determine to be one of at least two low-affinity subunits required for high-affinity IL-12 binding. These findings suggest that IL-4 and IFN-gamma exert opposite effects on T cell IL-12 responsiveness by differentially modulating the expression of low-affinity IL-12 receptor subunits that are distinct from IL-12Rbeta and required, together with IL-12Rbeta, for high-affinity IL-12 binding and IL-12 responsiveness. This provides a basis for understanding the interplay between different cytokines at the level of cytokine receptor expression, and offers insight into one of the mechanisms governing Th1 and Th2 development.

Increased interleukin 4 and immunoglobulin E production in transgenic mice overexpressing NK1 T cells

Natural Killer (NK)1.1+ (NK1) T cells are a specialized subset of alpha/beta T cells that coexpress surface receptors that are normally associated with the NK cell lineage of the innate immune system. On recognition of the conserved, major histocompatibility complex class I-like CD1 molecule, these cells are able to release explosive bursts of interleukin 4 (IL-4), a cytokine that promotes the T helper type 2 (Th2) effector class of an immune response. A unique feature of their T cell receptor (TCR) repertoire is the expression of an invariant TCR alpha chain, V alpha 14-J alpha 281, and of a restricted but polyclonal set of V beta gene families, V beta 8, V beta 7, and V beta 2. Here, we show that transgenic expression of this TCR alpha chain during thymic development is sufficient information to bias the differentiation of mainstream thymocytes towards the NK1 developmental pathway. It markedly increases the frequency of cells with the NK1 pattern of T cell differentiation and also has drastic consequences for the selection of the V beta repertoire. Transgenic CD4 cells exhibited a 10-100-fold increase in IL-4 production on mitogen stimulation in vitro and in vivo, and baseline levels of the Th2-controlled serum immunoglobulin isotypes, IgE and IgG1, were also selectively elevated in vivo.

Evidence for a predominant proinflammatory conjunctival cytokine response in individuals with trachoma

Immune responses to Chlamydia trachomatis infection in trachoma do not protect against reinfection or the development of scarring and blindness. In addition, the immunoregulatory contribution of cytokines to the development of conjunctival histopathology or protection is undefined. In this study, conjunctival cytokine mRNA transcripts were compared among subgroups of chlamydia infection status and ocular disease presentations of 50 individuals from an area where trachoma is endemic. There was a significant association of elevated interleukin (IL)-1beta, transforming growth factor beta1, and tumor necrosis factor alpha transcripts with infection, follicular inflammation, and scarring. Both gamma interferon (IFN-gamma) and IL-2 transcripts were significantly associated with infection; slightly elevated IL-2 levels were found in inflammatory disease. High IFN-gamma transcript levels were present with follicles and inflammatory disease and to a lesser extent with inflammatory scarring. The role of IFN-gamma in protection from infection or disease was not apparent from this study, since transcripts were frequently present in both chlamydial infection and disease. IL-12 (p40) transcripts were elevated in adults and children in association with follicular inflammation but not with scarring. IL-4, IL-5, and IL-10 transcripts were not detected in any samples. In conclusion, C. trachomatis infection stimulates local cytokines which favor a strong cell-mediated and proinflammatory response in both the early and later manifestations of trachoma. In addition, cytokine transcript levels that were associated with disease but no infection were characteristically lower overall than when chlamydia was present.

T lymphocytes from the normal human peritoneum contain high frequencies of Th2-type CD8+ T cells

The majority of peritoneal T lymphocytes have been shown to be CD8+ and to co-express CDw60. Expression of CDw60 characterizes CD8 T cells capable of secreting interleukin (IL)-4 and supporting IgG production by B cells. We analyzed at the clonal level the functional cytokine profile of CD8+ T lymphocytes from the normal human peritoneum. While the majority of the clones produced interferon (IFN)-gamma and exhibited high alloantigen-specific cytolytic activity, some clones secreted IL-4 and IL-5 but no detectable IFN-gamma. These Th2-type CD8+ T cell clones provided substantial B cell help for IgG and IgA synthesis and exhibited reduced cytolytic activity. Our results suggest that distinct subsets of CD8+ T cell may occur in different immune compartments.

Multiple host defense defects in failure of C57BL/6 ep/ep (pale ear) mice to resolve visceral Leishmania donovani infection

Euthymic C57BL/L ep/ep (pale ear [PE]) mice halt the visceral replication of intracellular Leishmania donovani but fail to properly resolve infection. A previous study identified an isolated defect in tissue granuloma formation in these mice; CD4+ and CD8+ cell number, gamma interferon (IFN-gamma) production, and macrophage antimicrobial activity in vitro were all intact. New in vivo results reported here suggest a considerably more complex immune defect, with evidence indicating (i) enhanced control over L. donovani after transfer of normal C57BL/6 spleen cells, (ii) a partially suppressive Th2 cell-associated response mediated by interleukin-4 (IL-4) but not reversed by CD4+ cell depletion, (iii) absent responses to endogenous Th1 cell lymphokines (IFN-gamma and IL-2) but preserved responsiveness to endogenous tumor necrosis factor alpha, (iv) absent responses to exogenous treatment with recognized antileishmanial cytokines (IFN-gamma, IL-2, IL-12, and granulocyte-macrophage colony-stimulating factor [GM-CSF]) not corrected by transfer of C57BL/6 spleen cells, and (v) a deficient response to antimony chemotherapy. Defective hepatic granuloma formation was not corrected by transfer of C57BL/6 spleen cells or by anti-IL-4 administration. While treatment with IL-2 and GM-CSF modified the tissue reaction and induced selected effector cells to encase tissue macrophages, no antileishmanial activity resulted. Together, these observations suggest that the failure of PE mice to resolve visceral L. donovani infection likely represents expression of multiple suboptimal immune responses and/or partial defects, probably involving a combination of T-cell dysfunction, a Th2 cell response, and target cell (macrophage) hyporesponsiveness.

Inhibition of NF-AT-dependent transcription by NF-kappa B: implications for differential gene expression in T helper cell subsets

Activation of individual CD4+ T cells results in differential lymphokine expression: interleukin 2 (IL-2) is preferentially produced by T helper type 1 (TH1) cells, which are involved in cell-mediated immune responses, whereas IL-4 is synthesized by TH2 cells, which are essential for humoral immunity. The Ca(2+)-dependent factor NF-ATp plays a key role in the inducible transcription of both these lymphokine genes. However, while IL2 expression requires the contribution of Ca(2+)- and protein kinase C-dependent signals, we report that activation of human IL4 transcription through the Ca(2+)-dependent pathway is diminished by protein kinase C stimulation in Jurkat T cells. This phenomenon is due to mutually exclusive binding of NF-ATp and NF-kappa B to the P sequence, an element located 69 bp upstream of the IL4 transcription initiation site. Human IL4 promoter-mediated transcription is downregulated in Jurkat cells stimulated with the NF-kappa B-activating cytokine tumor necrosis factor alpha and suppressed in RelA-overexpressing cells. In contrast, protein kinase C stimulation or RelA overexpression does not affect the activity of a human IL4 promoter containing a mouse P sequence, which is a higher-affinity site for NF-ATp and a lower-affinity site for RelA. Thus, competition between two general transcriptional activators, RelA and NF-ATp, mediates the inhibitory effect of protein kinase C stimulation on IL4 expression and may contribute to differential gene expression in TH cells.

Coordinate and cooperative roles for NF-AT and AP-1 in the regulation of the murine IL-4 gene

The transcription factor NF-AT plays an essential role in the inducible transcription of several cytokine genes during T cell activation. The distal NF-AT site of the murine IL-2 promoter binds both NF-AT and AP-1 proteins, and thus represents a composite regulatory site that integrates Ca(2+)- and PKC-dependent signaling pathways in T cell activation. However, the individual contributions of the NF-AT and AP-1 components to promoter activity via this composite site have not been resolved, owing to the absence of a clearly defined AP-1 binding site, which, when mutated abolishes AP-1 binding. We describe here an apparently analogous NF-AT/AP-1 composite site in the murine IL-4 promoter, which can be mutated to selectively block the recruitment of each component. We show that the cooperative and coordinate involvement of both NF-AT and AP-1 is necessary for full activity of the NF-AT/AP-1 composite site, and, ultimately, the entire IL-4 promoter.