PD-L1 and PD-L2 modulate airway inflammation and iNKT-cell-dependent airway hyperreactivity in opposing directions

Interactions of the inhibitory receptor programmed death-1 (PD-1) with its ligands, programmed death ligand (PD-L)1 and PD-L2, regulate T-cell activation and tolerance. In this study, we investigated the role of PD-L1 and PD-L2 in regulating invariant natural killer T (iNKT)-cell-mediated airway hyperreactivity (AHR) in a murine model of asthma. We found that the severity of AHR and airway inflammation is significantly greater in PD-L2(-/-) mice compared with wild-type mice after either ovalbumin (OVA) sensitization and challenge or administration of alpha-galactosylceramide (alpha-GalCer). iNKT cells from PD-L2(-/-) mice produced significantly more interleukin (IL)-4 than iNKT cells from control mice. Moreover, blockade of PD-L2 interactions of wild-type iNKT cells in vitro with monoclonal antibodies (mAbs) resulted in significantly enhanced levels of IL-4 production. In contrast, PD-L1(-/-) mice showed significantly reduced AHR and enhanced production of interferon-gamma (IFN-gamma) by iNKT cells. iNKT-deficient Jalpha18(-/-) mice reconstituted with iNKT cells from PD-L2(-/-) mice developed high levels of AHR, whereas mice reconstituted with iNKT cells from PD-L1(-/-) mice developed lower levels of AHR compared with control. As PD-L2 is not expressed on iNKT cells but rather is expressed on lung dendritic cells (DCs), in which its expression is upregulated by allergen challenge or IL-4, these findings suggest an important role of PD-L2 on lung DCs in modulating asthma pathogenesis. These studies also indicate that PD-L1 and PD-L2 have important but opposing roles in the regulation of AHR and iNKT-cell-mediated activation.

TIM gene family and their role in atopic diseases

The TIM gene family was discovered seven years ago by positional cloning in a mouse model of asthma and allergy. Three of the family members (TIM-1, TIM-3, and TIM-4) are conserved between mouse and man, and have been shown to critically regulate adaptive immunity. In addition, TIM-1 has been shown to play a major role as a human susceptibility gene for asthma, allergy and autoimmunity. Recently, TIM-4 has been identified as a ligand of phosphatidylserine and to control the uptake of apoptotic cells. These studies together suggest that the TIM gene family evolved to regulate immune responses by managing survival and cell death of hematopoetic cells.

iNKT cells in allergic disease

Recent studies indicate that invariant TCR+ CD1d-restricted natural killer T (iNKT) cells play an important role in regulating the development of asthma and allergy. iNKT cells can function to skew adaptive immunity toward Th2 responses, or can act directly as effector cells at mucosal surfaces in diseases such as ulcerative colitis and bronchial asthma. In mouse models of asthma, NKT cell-deficient strains fail to develop allergen-induced airway hyperreactivity (AHR), a cardinal feature of asthma, and NKT cells are found in the lungs of patients with chronic asthma, suggesting a critical role for NKT cells in the development of AHR. However, much work remains in characterizing iNKT cells and their function in asthma, and in understanding the relationship between the iNKT cells and conventional CD4+ T cells.

Spontaneous murine neuroaxonal dystrophy: a model of infantile neuroaxonal dystrophy

The neuroaxonal dystrophies (NADs) in human beings are fatal, inherited, neurodegenerative diseases with distinctive pathological features. This report describes a new mouse model of NAD that was identified as a spontaneous mutation in a BALB/c congenic mouse strain. The affected animals developed clinical signs of a sensory axonopathy consisting of hindlimb spasticity and ataxia as early as 3 weeks of age, with progression to paraparesis and severe morbidity by 6 months of age. Hallmark histological lesions consisted of spheroids (swollen axons), in the grey and white matter of the midbrain, brain stem, and all levels of the spinal cord. Ultrastructural analysis of the spheroids revealed accumulations of layered stacks of membranes and tubulovesicular elements, strongly resembling the ultrastructural changes seen in the axons of human patients with endogenous forms of NAD. Mouse NAD would therefore seem a potentially valuable model of human NADs.

Identification of Tapr (an airway hyperreactivity regulatory locus) and the linked Tim gene family

To simplify the analysis of asthma susceptibility genes located at human chromosome 5q23-35, we examined congenic mice that differed at the homologous chromosomal segment. We identified a Mendelian trait encoded by T cell and Airway Phenotype Regulator (Tapr). Tapr is genetically distinct from known cytokine genes and controls the development of airway hyperreactivity and T cell production of interleukin 4 (IL-4) and IL-13. Positional cloning identified a gene family that encodes T cell membrane proteins (TIMs); major sequence variants of this gene family (Tim) completely cosegregated with Tapr. The human homolog of TIM-1 is the hepatitis A virus (HAV) receptor, which may explain the inverse relationship between HAV infection and the development of atopy.

Critical role for IL-13 in the development of allergen-induced airway hyperreactivity

Airway hyperresponsiveness to a variety of specific and nonspecific stimuli is a cardinal feature of asthma, which affects nearly 10% of the population in industrialized countries. Eosinophilic pulmonary inflammation, eosinophil-derived products, as well as Th2 cytokines IL-13, IL-4, and IL-5, have been associated with the development of airway hyperreactivity (AHR), but the specific immunological basis underlying the development of AHR remains controversial. Herein we show that mice with targeted deletion of IL-13 failed to develop allergen-induced AHR, despite the presence of vigorous Th2-biased, eosinophilic pulmonary inflammation. However, AHR was restored in IL-13(-/-) mice by the administration of recombinant IL-13. Moreover, adoptive transfer of OVA-specific Th2 cells generated from TCR-transgenic IL-13(-/-) mice failed to induce AHR in recipient SCID mice, although such IL-13(-/-) Th2 cells produced high levels of IL-4 and IL-5 and induced significant airway inflammation. These studies definitively demonstrate that IL-13 is necessary and sufficient for the induction of AHR and that eosinophilic airway inflammation in the absence of IL-13 is inadequate for the induction of AHR. Therefore, treatment of human asthma with antagonists of IL-13 may be very effective.

Pulmonary dendritic cells producing IL-10 mediate tolerance induced by respiratory exposure to antigen

Respiratory exposure to allergen induces T cell tolerance and protection against the development of airway hyperreactivity and asthma. However, the specific mechanisms by which tolerance is induced by respiratory allergen are not clear. We report here that pulmonary dendritic cells (DCs) from mice exposed to respiratory antigen transiently produced interleukin 10 (IL-10). These phenotypically mature pulmonary DCs, which were B-7(hi) as well as producing IL-10, stimulated the development of CD4(+) T regulatory 1--like cells that also produced high amounts of IL-10. In addition, adoptive transfer of pulmonary DCs from IL-10(+/+), but not IL-10(-/-), mice exposed to respiratory antigen induced antigen-specific unresponsiveness in recipient mice. These studies show that IL-10 production by DCs is critical for the induction of tolerance, and that phenotypically mature pulmonary DCs mediate tolerance induced by respiratory exposure to antigen.

Il-18 gene transfer by adenovirus prevents the development of and reverses established allergen-induced airway hyperreactivity

We examined the role of IL-18 in preventing the development of and in reversing established allergen-induced airway inflammation and airway hyperreactivity (AHR), the cardinal features of asthma. IL-18, which potently induces IFN-gamma, was administered into the respiratory tract as cDNA in a replication-deficient adenovirus (Adv). Treatment of OVA-sensitized mice with the IL-18-expressing Adv reduced allergen-specific IL-4 production, airway eosinophilia, and mucus production, increased IFN-gamma production, and prevented the development of AHR. The effects of the IL-18 Adv treatment were dependent on the presence of IFN-gamma and IL-12. Moreover, administration of the IL-18 Adv to mice with established AHR greatly reduced AHR and IL-4 production and increased IFN-gamma production. These results demonstrate that IL-18, when administered by Adv into the respiratory tract, effectively reduces AHR and replaces an established Th2-biased immune response with a Th1-biased response.

Human alveolar macrophages induce functional inactivation in antigen-specific CD4 T cells

BACKGROUND

Alveolar macrophages (AMCs) are the most abundant phagocytic cells in the lung, but they present antigen poorly to T cells.

OBJECTIVES

The objectives of our studies were to more clearly define the mechanisms by which AMCs present antigen to T cells and to determine whether AMCs actively inhibit T-cell activation.

METHODS

We studied purified human CD4 T cells and compared the capacity of allogeneic AMCs and peripheral blood monocytes to induce T-cell proliferation and cytokine production.

RESULTS

We previously demonstrated that human AMCs fail to upregulate expression of B7-1 and B7-2 on stimulation with IFN-gamma. We now demonstrate that AMCs actively induce T-cell unresponsiveness (functional inactivation) in an antigen-specific manner and reduce the capacity of CD4 T cells to respond on secondary stimulation. The induction of unresponsiveness was reversed by the addition of CD28 costimulation or IL-2. However, interruption of Fas/Fas ligand interactions or of B7/CTLA-4 interactions did not prevent unresponsiveness, indicating that neither CTLA-4 triggering nor Fas-induced apoptosis was involved in the induction of T-cell unresponsiveness.

CONCLUSIONS

These studies indicate that AMCs actively tolerize CD4 T cells in an antigen-specific fashion. We propose that AMCs mediate a form of immune privilege in the lungs that effectively limits immune responses in the pulmonary compartment but has little effect on systemic immunity.

Vaccination with allergen-IL-18 fusion DNA protects against, and reverses established, airway hyperreactivity in a murine asthma model

Vaccination with naked DNA encoding a specific allergen has been shown previously to prevent, but not reverse, the development of allergen-induced airway hyperresponsiveness (AHR). To enhance the effectiveness of DNA vaccine therapies and make possible the treatment of established AHR, we developed a DNA vaccination plasmid containing OVA cDNA fused to IL-18 cDNA. Vaccination of naive mice either with this fusion DNA construct or with an OVA cDNA-containing plasmid protected the mice from the subsequent induction of AHR. Protection from AHR correlated with increased IFN-gamma production and reduced OVA-specific IgE production. The protection appeared to be mediated by IFN-gamma and CD8(+) cells because treatment of mice with neutralizing anti-IFN-gamma mAb or with depleting anti-CD8 mAb abolished the protective effect. Moreover, vaccination of mice with preexisting AHR with the OVA-IL-18 fusion DNA, but not with the OVA cDNA plasmid, reversed established AHR, reduced allergen-specific IL-4, and increased allergen-specific IFN-gamma production. Thus, combining IL-18 cDNA with OVA cDNA resulted in a vaccine construct that protected against the development of AHR, and that was unique among cDNA constructs in its capacity to reverse established AHR.

Allergen immunotherapy: novel approaches in the management of allergic diseases and asthma

Currently available pharmacotherapies for allergic diseases and asthma, which are serious public health problems, are aimed primarily at neutralizing effector molecules and inflammatory mediators such as histamine and leukotrienes or at inhibiting the function of inflammatory cells such as eosinophils and Th2 lymphocytes. While this approach is effective in controlling symptoms, these therapies have a limited capacity to alter the natural course of allergic diseases and asthma, and discontinuation of medications results in the redevelopment of symptoms on reexposure to the offending allergens. In contrast, immune-based allergen immunotherapies modify and correct the underlying pathological immune responses in allergy and asthma in an antigen-specific manner. These immunotherapies replicate the regulatory processes that occur in nonallergic individuals and allow patients to tolerate exposure to allergens. Current and future methodologies for immunotherapy involve immunization with allergen, modified allergen, peptides of allergen, cDNA of allergen, with adjuvants, including immunostimulatory DNA sequences, cytokines, and bacterial products such as Listeria monocytogenes. This form of therapy can provide a long-lasting cure for allergic diseases without the need for continuous therapeutic intervention and without causing generalized immunosuppression or immune augmentation.

Allergen-induced airway hyperreactivity is diminished in CD81-deficient mice

We demonstrated previously that CD81(-/-) mice have an impaired Th2 response. To determine whether this impairment affected allergen-induced airway hyperreactivity (AHR), CD81(-/-) BALB/c mice and CD81(+/+) littermates were sensitized i.p. and challenged intranasally with OVA. Although wild type developed severe AHR, CD81(-/-) mice showed normal airway reactivity and reduced airway inflammation. Nevertheless, OVA-specific T cell proliferation was similar in both groups of mice. Analysis of cytokines secreted by the responding CD81(-/-) T cells, particularly those derived from peribronchial draining lymph nodes, revealed a dramatic reduction in IL-4, IL-5, and IL-13 synthesis. The decrease in cytokine production was not due to an intrinsic T cell deficiency because naive CD81(-/-) T cells responded to polyclonal Th1 and Th2 stimulation with normal proliferation and cytokine production. Moreover, there was an increase in T cells and a decrease in B cells in peribronchial lymph nodes and in spleens of immunized CD81(-/-) mice compared with wild-type animals. Interestingly, OVA-specific Ig levels, including IgE, were similar in CD81(-/-) and CD81(+/+) mice. Thus, CD81 plays a role in the development of AHR not by influencing Ag-specific IgE production but by regulating local cytokine production.

Vaccination with heat-killed Listeria as adjuvant reverses established allergen-induced airway hyperreactivity and inflammation: role of CD8+ T cells and IL-18

Asthma is a respiratory disorder characterized by airway hyperreactivity (AHR) and inflammation and is associated with high serum IgE and overproduction of IL-4, IL-5, and IL-13 by allergen-specific Th2 cells. Our previous studies demonstrated that heat-killed Listeria monocytogenes (HKL) as an adjuvant in immunotherapy successfully reversed ongoing Ag-specific Th2-dominated responses toward Th1-dominated responses, but it was unclear if such immune modulation could reverse ongoing, established disease in target organs such as the lung. In this paper we show that a single dose of Ag plus HKL as adjuvant significantly reduced AHR in a murine model for asthma and reversed established AHR when given late after allergen sensitization. HKL as adjuvant also dramatically inhibited airway inflammation, eosinophilia, and mucus production, significantly reduced Ag-specific IgE and IL-4 production, and dramatically increased Ag-specific IFN-gamma synthesis. The inhibitory effect of HKL on AHR depended on the presence of IL-12 and CD8+ T cells and was associated with an increase of IL-18 mRNA expression. Thus, our results demonstrate that HKL as an adjuvant for immunotherapy mediates immune deviation from a pathological Th2-dominated response toward a protective immune response in peripheral lymphoid tissues and in the lungs and may be clinically effective in the treatment of patients with established asthma and allergic disease.

CD4(+) T helper cells engineered to produce latent TGF-beta1 reverse allergen-induced airway hyperreactivity and inflammation

T helper 2 (Th2) cells play a critical role in the pathogenesis of asthma, but the precise immunological mechanisms that inhibit Th2 cell function in vivo are not well understood. Using gene therapy, we demonstrated that ovalbumin-specific (OVA-specific) Th cells engineered to express latent TGF-beta abolished airway hyperreactivity and airway inflammation induced by OVA-specific Th2 effector cells in SCID and BALB/c mice. These effects correlated with increased concentrations of active TGF-beta in the bronchoalveolar lavage (BAL) fluid, demonstrating that latent TGF-beta was activated in the inflammatory environment. In contrast, OVA-specific Th1 cells failed to inhibit airway hyperreactivity and inflammation in this system. The inhibitory effect of TGF-beta-secreting Th cells was antigen-specific and was reversed by neutralization of TGF-beta. Our results demonstrate that T cells secreting TGF-beta in the respiratory mucosa can indeed regulate Th2-induced airway hyperreactivity and inflammation and suggest that TGF-beta-producing T cells play an important regulatory role in asthma.

Intranasal exposure to protein antigen induces immunological tolerance mediated by functionally disabled CD4+ T cells

In this study we examined the immunological parameters underlying the natural immunity to inhaled nonpathogenic proteins. We addressed this question by examining the effect of intranasal exposure to OVA in both wild-type mice and mice reconstituted with OVA-TCR transgenic CD4+ T cells. Intranasal administration of OVA induced an initial phase of activation during which CD4+ T cells were capable of proliferating and producing cytokines. Although many of the OVA-specific CD4+ T cells were subsequently depleted from the lymphoid organs, a stable population of such T cells survived but remained refractory to antigenic rechallenge. The unresponsive state was not associated with immune deviation due to selective secretion of Th1- or Th2-type cytokines, and the presence of regulatory CD8+ T cells was not required. Moreover, neutralization of the immunosuppressive cytokines IL-10 and TGF-beta did not abrogate the induction of tolerance. Inhibition of the interaction of T cells with CD86, but not CD80, at the time of exposure to intranasal Ag prevented the development of unresponsiveness, while selective blockade of CTLA-4 had no effect. Our results suggest that intranasal exposure to Ags results in immunological tolerance mediated by functionally impaired CD4+ T cells via a costimulatory pathway that requires CD86.

The kinetics of change in cytokine production by CD4 T cells during conventional allergen immunotherapy

BACKGROUND

The effect of conventional allergen immunotherapy on allergen-specific T lymphocyte cytokine production is incompletely understood, particularly during the initial phase of treatment.

OBJECTIVE

The purpose of this study was to prospectively follow the kinetics of change in CD4(+) T cell cytokine secretion during the course of conventional immunotherapy.

METHODS

Six allergic individuals were treated with extracts of Dermatophagoides farinae/Dermatophagoides pteronyssinus or with rye grass pollen (Lolium perenne) allergen, but not both, by using an internally controlled conventional immunotherapy protocol. CD4(+) T cells from peripheral blood were examined in vitro at varying intervals after the initiation of immunotherapy by stimulation with D farinae or L perenne group I antigen. The quantity of IL-4 and IFN-gamma produced and its relationship to clinical improvement was determined.

RESULTS

The ratio of allergen-specific IL-4/IFN-gamma production by CD4(+) T cells from 4 of 6 individuals receiving immunotherapy greatly increased during the period when the dose of allergen was increasing. However, after high-dose maintenance therapy was achieved, this ratio decreased in subjects responding clinically to, but not in those failing, immunotherapy. In addition, late-phase skin reactions and allergen-specific IgE levels in responding, but not in nonresponding, subjects diminished over the course of immunotherapy.

CONCLUSION

Conventional immunotherapy may initially exacerbate allergic disease by increasing allergen-specific IL-4 and allergen-specific IgE production. Later clinical improvement is associated with a reduction in allergen-specific IL-4 production and in allergen-specific serum IgE.

Allergen-specific Th1 cells fail to counterbalance Th2 cell-induced airway hyperreactivity but cause severe airway inflammation

Allergic asthma, which is present in as many as 10% of individuals in industrialized nations, is characterized by chronic airway inflammation and hyperreactivity induced by allergen-specific Th2 cells secreting interleukin-4 (IL-4) and IL-5. Because Th1 cells antagonize Th2 cell functions, it has been proposed that immune deviation toward Th1 can protect against asthma and allergies. Using an adoptive transfer system, we assessed the roles of Th1, Th2, and Th0 cells in a mouse model of asthma and examined the capacity of Th1 cells to counterbalance the proasthmatic effects of Th2 cells. Th1, Th2, and Th0 lines were generated from ovalbumin (OVA)-specific T-cell receptor (TCR) transgenic mice and transferred into lymphocyte-deficient, OVA-treated severe combined immunodeficiency (SCID) mice. OVA-specific Th2 and Th0 cells induced significant airway hyperreactivity and inflammation. Surprisingly, Th1 cells did not attenuate Th2 cell-induced airway hyperreactivity and inflammation in either SCID mice or in OVA-immunized immunocompetent BALB/c mice, but rather caused severe airway inflammation. These results indicate that antigen-specific Th1 cells may not protect or prevent Th2-mediated allergic disease, but rather may cause acute lung pathology. These findings have significant implications with regard to current therapeutic goals in asthma and allergy and suggest that conversion of Th2-dominated allergic inflammatory responses into Th1-dominated responses may lead to further problems.

Cytotoxic T cell responses to DNA vaccination: dependence on antigen presentation via class II MHC

This study was designed to test whether cytotoxic T cell (CTL) responses to DNA vaccination are dependent upon MHC class II-restricted priming of CD4+ T cells. Because DNA vaccination may directly transfect dendritic cells, and dendritic cells may be capable of directly stimulating CD8+ T cell responses, such priming might be unnecessary. To test this hypothesis, C57BL/6 mice were immunized intramuscularly or intradermally with DNA encoding either whole OVA, a class I (Kb)-restricted peptide epitope of OVA (amino acids 257-264, SIINFEKL), or this class I-restricted epitope plus the adjacent class II (I-Ab)-restricted epitope of OVA (amino acids 265-280, TEWTSSNVMEERKIKV). Very low to negligible CTL responses were observed in mice vaccinated with the SIINFEKL construct, whereas mice vaccinated with the SIINFEKLTEWTSSNVMEERKIKV or with the complete OVA construct made equally robust CTL responses. These responses were sensitive to blocking by anti-CD8 mAb and were shown to be SIINFEKL-specific by using SIINFEKL peptide-pulsed EL-4 cells as targets. To ensure that the generation of these CTL responses was indeed dependent upon CD4+ T cell help, mice were depleted of either CD4+ or CD8+ cells before immunization. Depletion of CD4+ cells completely abrogated the CTL response to OVA DNA, as did depletion of CD8+ cells. Thus, we conclude that the CTL response to both intramuscular and intradermal DNA vaccination is highly dependent upon the generation of CD4+ T cell help via a class II MHC-dependent pathway. These results will be relevant for the construction of minimal-epitope vaccines for DNA immunization.

Heat-killed Listeria monocytogenes as an adjuvant converts established murine Th2-dominated immune responses into Th1-dominated responses

We investigated the capacity of heat-killed Listeria monocytogenes (HKL), a potent stimulator of the innate immune system, as a vaccine adjuvant to modify both primary and secondary Ag-specific immune responses. Mice immunized with the Ag keyhole limpet hemocyanin (KLH) mixed with HKL generated a KLH-specific primary response characterized by production of Th1 cytokines and large quantities of KLH-specific IgG2a Ab. Moreover, administration of KLH with HKL as an adjuvant reversed established immune responses dominated by the production of Th2 cytokines and high levels of KLH-specific IgE and induced a Th1-type response with high levels of IFN-gamma and IgG2a and low levels of IgE and IL-4. Neutralization of IL-12 activity at the time of HKL administration blocked the enhancement of IFN-gamma and reduction of IL-4 production, indicating that IL-12, induced by HKL, was responsible for the adjuvant effects on cytokine production. These results suggest that HKL as an adjuvant during immunization can successfully bias the development of Ag-specific cytokine synthesis toward Th1 cytokine production even in the setting of an ongoing Th2-dominated response. Thus, HKL may be clinically effective in vaccine therapies for diseases such as allergy and asthma, which require the conversion of Th2-dominated immune responses into Th1-dominated responses.

Reduced prevalence of allergic disease in patients with multiple sclerosis is associated with enhanced IL-12 production

BACKGROUND

We previously showed that the prevalence of allergic disease is decreased in patients with multiple sclerosis (MS); however, the mechanisms that explain this finding have not previously been defined.

OBJECTIVES

We have demonstrated that protection of patients with MS from allergic disease may be caused by the production in monocytes from these patients of elevated quantities of IL-12 compared with that observed in monocytes from individuals with allergies.

METHODS

Purified monocytes from peripheral blood of subjects with or without allergies and from individuals with MS were directly stimulated with Staphylococcus aureus Cowan strain I in the absence of T cells. IL-12 was quantitated by a sensitive reverse transcription, competitive PCR.

RESULTS

IL-12 production was 5-fold greater in monocytes from patients with MS (n = 11) than that from individuals with allergies (n = 10) (for subjects with MS, 1.90+/-0.18 vs 1.24+/-0.19 log10 fmol/microL for individuals with allergies) (P = .02). Although the production of IL-12 in monocytes from patients with MS was slightly higher than that from subjects without allergies, this difference was not statistically significant.

CONCLUSIONS

IL-12 production in individuals with MS is much greater than in individuals with allergies. Because IL-12 induces TH1 cytokine synthesis and reduces the production of TH2 cytokines, which amplify and prolong allergic inflammation, these studies suggest that enhanced IL-12 production may protect individuals with MS from the development of allergy but may predispose such individuals toward autoimmune inflammation in the central nervous system.

Corticosteroids enhance the capacity of macrophages to induce Th2 cytokine synthesis in CD4+ lymphocytes by inhibiting IL-12 production

We investigated the effects of corticosteroids on IL-12 production by mouse splenic adherent cells and the subsequent capacity of these cells to induce cytokine production by CD4+ T cells. To distinguish the effects of corticosteroids on APCs from those on T cells, only the APCs and not the T cells were exposed to corticosteroids. Treatment of splenic adherent cells with dexamethasone greatly inhibited production of IL-12, a cytokine known to enhance IFN-gamma synthesis and decrease IL-4 synthesis by CD4+ T cells. The reduction in IL-12 production by corticosteroid-treated macrophages decreased their ability to induce IFN-gamma and increased their ability to induce IL-4 synthesis in Ag-primed CD4+ T cells. Splenic adherent cells from mice treated in vivo with dexamethasone also displayed a reduced capacity to produce IL-12. These results help to resolve previous conflicting observations regarding the effects of corticosteroids on cytokine production by T cells, and indicate that while corticosteroids may directly inhibit Th1 and Th2 cytokine production in T cells, corticosteroids, by reducing IL-12 production in APCs, have the potential to indirectly enhance Th2 cytokine synthesis. Therefore, treatment of diseases such as allergy with chronic corticosteroids may indirectly exacerbate the course of the disease, which is caused primarily by the overproduction of Th2 cytokines in allergen-specific CD4+ T cells.

Antigen-primed T cells from B cell-deficient JHD mice fail to provide B cell help

B cells are effective in presenting Ag to primed T cells, but a specific role for B cells in priming naive T cells has not been clearly established. In this report we demonstrate that Ag administration to B cell-deficient JHD mice primes T cells for Ag-specific proliferative responses, but such primed T cells fail to provide help for isotype switching and IgG production in B cells. Although T cells primed in the absence of B cells could proliferate in response to Ag presented by B cells and could induce Ag-specific IgM production, such T cells failed to produce high levels of IL-4 as are normally induced in T cells by Ag-presenting B cells. These findings suggest that while B cells are not absolutely required for T cell priming, they provide signals to T cells that are not replicated by other APCs and that influence the subsequent ability of T cells to interact with B cells.

DNA vaccination with cytokine fusion constructs biases the immune response to ovalbumin

DNA vaccination may work through direct transfection of antigen presenting cells (APC), or by secretion of the encoded protein by muscle or skin cells for uptake by APC. If cytokines are attached to the antigen, they may influence APC or responding T cells to drive the response toward a Th1 or Th2 direction, and/or potentiate it in an antigen-specific manner. To test this concept, expression vectors were constructed containing the ovalbumin (OVA) gene either alone, or linked to cytokine genes including GM-CSF, IFN-gamma, IL-2, IL-4, IL-12, or a sequence encoding nine amino acids of IL-1 beta. These constructs expressed OVA-cytokine fusion proteins in vitro which retained cytokine bioactivity. C57BL/6 mice were injected intramuscularly with the DNA constructs. Little if any OVA-specific antibody was produced in response to any of the DNA constructs, except for OVA-IL-4. However, lymphocytes from BALB/c mice vaccinated with OVA-IL-12 and OVA-IL-1 beta constructs produced more IFN-gamma and less IL-4 during in vitro restimulation assays than did other groups. All constructs elicited OVA-specific cytotoxic responses which were maintained or even increased over 16 weeks. The OVA-IL-12 and OVA-IL-1 beta peptide constructs elicited the strongest cytotoxic responses at 2 weeks postinjection. Cytotoxic responses were seen in all animals, even those lacking OVA-specific Ab, and were not related to Ab level. These studies indicate that the humoral, cytokine, and cytotoxic responses to DNA vaccination can be effectively altered by certain cytokine fusion constructs.

Corticosteroids inhibit IL-12 production in human monocytes and enhance their capacity to induce IL-4 synthesis in CD4+ lymphocytes

We examined the effects of corticosteroids on IL-12 production by human monocytes and on cytokine synthesis in T cells. To distinguish the effects of corticosteroids on the APC used to activate the T cell from direct effects of corticosteroids on the T cell, experiments were performed by exposing the APC and not the T cell to corticosteroids. We found that corticosteroids significantly inhibited the production in monocytes of IL-12, a cytokine that is extremely potent in enhancing IFN-gamma and inhibiting IL-4 synthesis in T cells. We demonstrated that reduced production of IL-12 in corticosteroid-treated monocytes resulted in a decreased capacity of the monocytes to induce IFN-gamma and an increased ability to induce IL-4 in T cells. These results suggest that although corticosteroids may be beneficial for the treatment of asthma or allergic disease due to direct inhibitory effects of corticosteroids on cytokine synthesis in T cells, chronic corticosteroid therapy may indirectly exacerbate the long-term course of allergic disease. This deleterious effect of corticosteroids would result from a limitation in IL-12 production in tissue monocytes and macrophages, which would enhance production of Th2 cytokines (which augment allergic disease), and would reduce production of Th1 cytokines (which attenuate allergic disease) in T cells that subsequently infiltrate the tissues.

Corticosteroids inhibit IL-12 production in human monocytes and enhance their capacity to induce IL-4 synthesis in CD4+ lymphocytes

We examined the effects of corticosteroids on IL-12 production by human monocytes and on cytokine synthesis in T cells. To distinguish the effects of corticosteroids on the APC used to activate the T cell from direct effects of corticosteroids on the T cell, experiments were performed by exposing the APC and not the T cell to corticosteroids. We found that corticosteroids significantly inhibited the production in monocytes of IL-12, a cytokine that is extremely potent in enhancing IFN-gamma and inhibiting IL-4 synthesis in T cells. We demonstrated that reduced production of IL-12 in corticosteroid-treated monocytes resulted in a decreased capacity of the monocytes to induce IFN-gamma and an increased ability to induce IL-4 in T cells. These results suggest that although corticosteroids may be beneficial for the treatment of asthma or allergic disease due to direct inhibitory effects of corticosteroids on cytokine synthesis in T cells, chronic corticosteroid therapy may indirectly exacerbate the long-term course of allergic disease. This deleterious effect of corticosteroids would result from a limitation in IL-12 production in tissue monocytes and macrophages, which would enhance production of Th2 cytokines (which augment allergic disease), and would reduce production of Th1 cytokines (which attenuate allergic disease) in T cells that subsequently infiltrate the tissues.

Antigen-specific B cells preferentially induce CD4+ T cells to produce IL-4

The role of Ag presentation by B cells in regulating the development of T cells with restricted cytokine profiles remains controversial. In this report, we compared Ag presentation by naive polyclonal B cells, naive Ag-specific B cells (from Ig receptor transgenic mice), or splenic adherent cells (SAC) and examined the capacity of these cells to influence cytokine production by CD4+ T cells. Freshly isolated naive B cells stimulated vigorous T cell proliferation and very strong T cell cytokine responses, but only when cultured with Ag recognized by the B cell Ig receptor (cognate Ag) and not when cultured with a noncognate Ag. Under these conditions, B cells activated by Ig receptor-mediated endocytosis of Ag induced both naive and Ag-primed CD4+ T cells to produce high levels of IL-4 (300-4000 pg/ml). In contrast, SAC induced the production of very low levels of IL-4 (<100 pg/ml) but much higher maximal levels of IFN-gamma than did Ag-specific B cells. The induction of IL-4 synthesis by Ag-specific B cells was significantly reduced by blocking CD40-CD40 ligand (CD40L) interactions or by the addition of small quantities of rIL-12. These results suggest that B cells activated by their cognate Ag preferentially induce IL-4 synthesis as a result of the interaction of CD40L on T cells with CD40, whereas SAC preferentially induce IFN-gamma synthesis by T cells as a result of their greater production of IL-12 and their limited capacity to trigger CD40L on T cells.

Th1 and Th2 CD4+ cells in the pathogenesis of allergic diseases

Our understanding of the molecular and genetic etiologies of allergic disorders, which affect 20%-30% of the general population, has greatly improved over the past several years. Previously, research focused on examination of immediate hypersensitivity reactions, initiated by the cross-linking of IgE molecules on the surface of mast cells/basophils, resulting in the release of a host of mediators, which cause symptoms typified by acute anaphylaxis. Although there has been substantial progress in understanding the molecular biology of mast cell and basophil activation and of the regulation of IgE synthesis, recent studies have shifted attention to the cellular and molecular mechanisms that cause a broader allergic inflammatory response and underlie the more chronic and severe symptoms of allergy and asthma. In this report, we will review a substantial body of recent experimental work that has provided the basis for our new understanding of the allergic inflammatory response and the pathogenesis of allergic diseases. We will describe the recent progress in defining the immunological basis for allergic disease, and how subsets of helper CD4+ T cells secreting a specific array of cytokines (Th2 cytokines) regulate/cause allergic inflammation. We will review the cell biology of Th2 cells, the role of Th2 cells in allergic disease, and biological, genetic, and therapeutic mechanisms that influence the differentiation of CD4+ T cells and enhance or suppress cytokine synthesis in Th2 cells. These mechanisms control the expression of allergic diseases, which occur in some but not all individuals following environmental exposure to allergens.

An ovalbumin-IL-12 fusion protein is more effective than ovalbumin plus free recombinant IL-12 in inducing a T helper cell type 1-dominated immune response and inhibiting antigen-specific IgE production

Optimal treatment of allergic diseases requires that the cytokine profile of allergen-specific T cells be redirected, with the conversion of Th2 profiles into Th1 cytokine profiles. This conversion, however, is difficult, since Th2 effector cells have relatively fixed cytokine profiles. To more effectively redirect the cytokine profiles of T cells, we constructed a cytokine fusion protein that contained the Ag OVA, fused to IL-12. Immunization with the OVA-IL-12 fusion protein induced anti-OVA IgG2a Ab and large quantities of OVA-specific IFN-gamma production. The Ag specificity of this response was dependent upon covalent linkage of Ag and IL-12, since immunization of mice with OVA alone induced little or no IFN-gamma, while immunization with OVA and free rIL-12 enhanced T cell production of IFN-gamma, but the IFN-gamma production was not OVA specific. To examine the effects of OVA-IL-12 in reversing ongoing Th2-dominated immune responses, BALB/c mice previously primed with OVA in alum to induce a Th2-dominated response, were vaccinated with the OVA-IL-12 protein. In such mice, OVA-IL-12 was much more effective than OVA plus free rIL-12 in significantly increasing Ag-specific IFN-gamma production and significantly decreasing Ag-specific IL-4 production. Moreover, OVA-IL-12 increased serum anti-OVA IgG2a and decreased anti-OVA IgE. These studies indicate that OVA-IL-12 can convert immune responses characterized by high IL-4 and high IgE synthesis into Th1-dominated responses in an Ag-specific manner.

Antigen-specific B cells preferentially induce CD4+ T cells to produce IL-4

The role of Ag presentation by B cells in regulating the development of T cells with restricted cytokine profiles remains controversial. In this report, we compared Ag presentation by naive polyclonal B cells, naive Ag-specific B cells (from Ig receptor transgenic mice), or splenic adherent cells (SAC) and examined the capacity of these cells to influence cytokine production by CD4+ T cells. Freshly isolated naive B cells stimulated vigorous T cell proliferation and very strong T cell cytokine responses, but only when cultured with Ag recognized by the B cell Ig receptor (cognate Ag) and not when cultured with a noncognate Ag. Under these conditions, B cells activated by Ig receptor-mediated endocytosis of Ag induced both naive and Ag-primed CD4+ T cells to produce high levels of IL-4 (300-4000 pg/ml). In contrast, SAC induced the production of very low levels of IL-4 (&lt;100 pg/ml) but much higher maximal levels of IFN-gamma than did Ag-specific B cells. The induction of IL-4 synthesis by Ag-specific B cells was significantly reduced by blocking CD40-CD40 ligand (CD40L) interactions or by the addition of small quantities of rIL-12. These results suggest that B cells activated by their cognate Ag preferentially induce IL-4 synthesis as a result of the interaction of CD40L on T cells with CD40, whereas SAC preferentially induce IFN-gamma synthesis by T cells as a result of their greater production of IL-12 and their limited capacity to trigger CD40L on T cells.

An ovalbumin-IL-12 fusion protein is more effective than ovalbumin plus free recombinant IL-12 in inducing a T helper cell type 1-dominated immune response and inhibiting antigen-specific IgE production

Optimal treatment of allergic diseases requires that the cytokine profile of allergen-specific T cells be redirected, with the conversion of Th2 profiles into Th1 cytokine profiles. This conversion, however, is difficult, since Th2 effector cells have relatively fixed cytokine profiles. To more effectively redirect the cytokine profiles of T cells, we constructed a cytokine fusion protein that contained the Ag OVA, fused to IL-12. Immunization with the OVA-IL-12 fusion protein induced anti-OVA IgG2a Ab and large quantities of OVA-specific IFN-gamma production. The Ag specificity of this response was dependent upon covalent linkage of Ag and IL-12, since immunization of mice with OVA alone induced little or no IFN-gamma, while immunization with OVA and free rIL-12 enhanced T cell production of IFN-gamma, but the IFN-gamma production was not OVA specific. To examine the effects of OVA-IL-12 in reversing ongoing Th2-dominated immune responses, BALB/c mice previously primed with OVA in alum to induce a Th2-dominated response, were vaccinated with the OVA-IL-12 protein. In such mice, OVA-IL-12 was much more effective than OVA plus free rIL-12 in significantly increasing Ag-specific IFN-gamma production and significantly decreasing Ag-specific IL-4 production. Moreover, OVA-IL-12 increased serum anti-OVA IgG2a and decreased anti-OVA IgE. These studies indicate that OVA-IL-12 can convert immune responses characterized by high IL-4 and high IgE synthesis into Th1-dominated responses in an Ag-specific manner.

Novel genetic regulation of T helper 1 (Th1)/Th2 cytokine production and encephalitogenicity in inbred mouse strains

Development of T helper cell (Th)1 or Th2 cytokine responses is essential for effector and regulatory functions of T helper cells. We have compared cytokine profiles of myelin basic protein (MBP) Ac1-16 peptide-specific T helper cells from inbred mouse strains expressing identical k haplotype-derived MHC class II molecules B10.A and B10.BR, B10.BR T cell lines (TCL) produced Th1 cytokines (including high levels of TNF-alpha) and induced experimental autoimmune encephalomyelitis after adoptive transfer. In contrast, B10.A TCL produced Th2 cytokines (including low levels of TNF-alpha) and were poorly encephalitogenic. The contributions of the genetic origin of the T cells and the APC were explored. Serial restimulations of the B10.BR TCL with B10.A or (B10.A x B10.BR) F1 splenic antigen presenting cells (APC) during the establishment of TCL markedly reduced both Th1 cytokine production and encephalitogenicity. In addition, a single restimulation with B10. A splenic APC reduced IFN-gamma and TNF-alpha production by established Th1 MBP-specific Ak-restricted B10.BR TCL and by a Th1 KLH-specific, Ek-restricted B10.BR T cell clone. These studies suggest that B10.A and B10.BR APC differ in their ability to stimulate IFN-gamma and TNF-alpha production by mature Th1 cells and also influence their Th1/Th2 commitment in vivo. The nature of the downregulatory activity of B10.A APC on IFN-gamma and TNF-alpha production was explored. 2-hour supernatants from antigen-activated B10.A APC/TCL cultures or from B10.A APC activated by LPS had the same inhibitory effects on IFN-gamma and TNF-alpha production by B10.BR TCL. The downregulatory effects of B10.A APC are independent of TNF-alpha, IL-4, IL-10, IL-12p40, IFN-gamma, IL-13, TGF-beta, and PGE2. Thus, genetic difference(s) between B10.A and B10.BR APC appear(s) to control the production or activity of a novel soluble cytokine regulatory factor that influences Th1/Th2 commitment and controls production of IFN-gamma and TNF-alpha by mature Th1 cells.

Ly1- (CD5-) B cells produce interleukin (IL)-10

Interleukin (IL)-10 enhances humoral immunity by inhibiting macrophage activation and promoting the development of Th2 cytokine synthesis. In this study we investigated the ability of conventional Ly-1- (CD5-) B cells to produce IL-10 protein. Highly purified normal, naive splenic B cells from both BALB/c and C57BL/6 mice produced IL-10 in response to stimulation with the mitogen LPS. In addition, B cells from antigen primed mice also produced IL-10 upon antigen restimulation in vitro, as analyzed by ELISA and by bioassay. Removal of Ly-1+ B cells did not appreciably reduce IL-10 production, indicating that conventional Ly-1- B cells produced IL-10. These results indicate that normal Ly-1- B cells produce significant quantities of IL-10 during mitogen- or antigen-driven immune responses. The production of IL-10 by conventional B cells may enhance their capacity to promote humoral immune responses.

Antigen-driven but not lipopolysaccharide-driven IL-12 production in macrophages requires triggering of CD40

We demonstrated that two distinct pathways exist for the induction of IL-12 in APC. The first pathway for IL-12 production occurred during responses to T cell-dependent Ags such as OVA and required triggering of CD40 molecules on the APC. IL-12 production in this T cell-dependent system increased in direct proportion to Ag concentration and required TCR ligation but not CD28 costimulation. The second pathway occurred when bacterial products such as LPS or heat-killed Listeria monocytogenes were used to activate macrophages to produce IL-12 in the complete absence of T cells. In this second pathway, IL-12 production was completely independent of CD40 triggering. In both pathways, the presence of IFN-gamma was not required for induction of IL-12 synthesis when splenic adherent cells (SAC) from normal mice were used. However, addition of IFN-gamma to cultures of Th2 T cells and SAC increased IL-12 production two- to fivefold, and addition of rTNF-alpha with IFN-gamma further enhanced IL-12 production. The addition of TNF-alpha in the absence of IFN-gamma, however, had no effect on IL-12 production in the T cell-dependent pathway. Similarly, addition of TNF-alpha in the presence or the absence of IFN-gamma to cultures of LPS or heat-killed Listeria and SAC did not increase IL-12 production, but addition of IFN-gamma alone greatly enhanced IL-12 production, consistent with the idea that bacterial stimuli induce significant quantities of endogenous TNF-alpha production. These results indicate that the requirements for the induction of IL-12 production in T cell-dependent and T cell-independent responses differs mainly with regard to CD40 triggering. Furthermore, these results suggest that IL-12 production can be induced by bacterial products in patients with hyper-IgM syndrome who lack CD40 ligand expression and in those treated with soluble gp39 to interrupt CD40-CD40 ligand interactions.

Antigen-driven but not lipopolysaccharide-driven IL-12 production in macrophages requires triggering of CD40

We demonstrated that two distinct pathways exist for the induction of IL-12 in APC. The first pathway for IL-12 production occurred during responses to T cell-dependent Ags such as OVA and required triggering of CD40 molecules on the APC. IL-12 production in this T cell-dependent system increased in direct proportion to Ag concentration and required TCR ligation but not CD28 costimulation. The second pathway occurred when bacterial products such as LPS or heat-killed Listeria monocytogenes were used to activate macrophages to produce IL-12 in the complete absence of T cells. In this second pathway, IL-12 production was completely independent of CD40 triggering. In both pathways, the presence of IFN-gamma was not required for induction of IL-12 synthesis when splenic adherent cells (SAC) from normal mice were used. However, addition of IFN-gamma to cultures of Th2 T cells and SAC increased IL-12 production two- to fivefold, and addition of rTNF-alpha with IFN-gamma further enhanced IL-12 production. The addition of TNF-alpha in the absence of IFN-gamma, however, had no effect on IL-12 production in the T cell-dependent pathway. Similarly, addition of TNF-alpha in the presence or the absence of IFN-gamma to cultures of LPS or heat-killed Listeria and SAC did not increase IL-12 production, but addition of IFN-gamma alone greatly enhanced IL-12 production, consistent with the idea that bacterial stimuli induce significant quantities of endogenous TNF-alpha production. These results indicate that the requirements for the induction of IL-12 production in T cell-dependent and T cell-independent responses differs mainly with regard to CD40 triggering. Furthermore, these results suggest that IL-12 production can be induced by bacterial products in patients with hyper-IgM syndrome who lack CD40 ligand expression and in those treated with soluble gp39 to interrupt CD40-CD40 ligand interactions.

Reconstitution of germinal center formation in nude mice with Th1 and Th2 clones

We investigated the ability of hemocyanin (KLH)-specific cloned CD4+ T cells expressing defined cytokine profiles to support germinal center (GC) formation in syngeneic athymic recipients in response to hapten-KLH challenge. Th1 clones producing IL-2 and IFN-gamma did not by themselves increase GC production above background, while Th2 cells producing IL-4 and IL-5 did. However, the combination of Th1 and Th2 cytokines was more effective than Th2 cytokines alone, suggesting a synergistic effect in this aspect of their help for B cells. In contrast to GC formation, antibody production could be induced with Th1 or Th2 clones given separately (Th1 clones inducing IgG2a, and Th2 clones inducing IgG1 and IgE). These results indicate that the T cell requirements for GC production are different from those for isotype switching and Ig secretion. It is postulated that the synergy between Th1 and Th2 cells in the induction of GC formation reflects the synergy between Th1 and Th2 cytokines, such as IFN-gamma and IL-5, in promotion of GC cell proliferation.

Differential production of IL-12 in BALB/c and DBA/2 mice controls IL-4 versus IFN-gamma synthesis in primed CD4 lymphocytes

The profile of cytokines produced by CD4 T cells is profoundly influenced by the presence of IL-12. Here we demonstrate that during re-stimulation of antigen-specific immune responses in vitro, antigen-primed lymph node cells from DBA/2 mice produced 3- to 30-fold more IL-12 than did cells from BALB/c mice, which are identical at the major histocompatibility locus. The strain differences in IL-12 production were observed only in antigen-driven responses (and not in responses induced by bacterial products), and were dependent upon an interaction between CD4 T cells and lymph node adherent cells. In addition, differences in the quantity of IL-12 produced by DBA/2 and BALB/c antigen-presenting cells (APC) was not dependent on differential production of IFN-gamma by T cells, since APC from DBA/2 mice still produced much greater quantities of IL-12 than did BALB/c APC when each was cultured with the same H-2d-restricted Th2 clones, in the complete absence of IFN-gamma, or when each was cultured with primed (BALB/c x DBA/2)F1 T cells. The level of IL-12 produced in the cultures critically affected cytokine production in CD4 T cells, since neutralization of endogenous IL-12 in DBA/2 cultures, which are predisposed towards developing Th1 responses, reduced IFN-gamma production and enhanced IL-4 synthesis to levels normally seen in BALB/c cultures, which are predisposed toward developing Th2 responses. We propose therefore that differential production of antigen-driven IL-12 is a mechanism by which the genetic background in DBA/2 and BALB/c mice can affect the pattern of cytokine synthesis by T cells during the development of adaptive immune responses.

Ligation of TAPA-1 (CD81) or major histocompatibility complex class II in co-cultures of human B and T lymphocytes enhances interleukin-4 synthesis by antigen-specific CD4+ T cells

We have previously shown that CD4+ T cells from allergic individuals are predisposed to producing interleukin (IL)-4 in response to allergens. IL-4 production could be modulated by antigen concentration as well as by the type of antigen-presenting cells (APC), with B lymphocytes inducing greater quantities of IL-4 than monocytes. Using this system we examined IL-4 synthesis after culture of CD4+ T cells with B cells, monocytes, or both, as APC in the presence of allergen and a monoclonal antibody against CD81 (TAPA-1), a member of the TM4 superfamily of proteins that regulates activation, proliferation and trafficking of B cells. Addition of anti-CD81 mAb during culture enhanced IL-4 synthesis by 2- to 70-fold over that using an isotype-matched control mAb. Furthermore, anti-CD81 mAb enhanced IL-4 synthesis in CD4+ T cells only when CD4+ T cells were cultured with B cells but not monocytes as APC, indicating that anti-CD81 mAb affected IL-4 synthesis in T cells via interactions with B cells. However, pretreatment of either population separately with anti-CD81 mAb prior to culture had no effect on subsequent IL-4 synthesis, suggesting a requirement for temporal or cooperative interactions between T and B lymphocytes. In addition, anti-CD81 mAb enhanced IL-4 production but reduced CD4+ T cell antigen-specific proliferation, demonstrating that IL-4 production and proliferation by CD4+ T cells were inversely related. Finally, mAb to major histocompatibility complex class II but not to anti-CD19 also enhanced IL-4 synthesis when B lymphocytes were used as APC. In all instances, enhancement of CD4+ IL-4 synthesis correlated with the presence of large cell aggregates in T-B lymphocyte cocultures. These results indicate that the capacity of B cells to induce IL-4 can be significantly enhanced by ligation of particular molecules on their surface and should aid in the design of treatments for diseases in which modulation of the cytokine profile would be beneficial.

Cross-linking of the CD40 ligand on human CD4+ T lymphocytes generates a costimulatory signal that up-regulates IL-4 synthesis

Although there is good evidence that the induction of IL-4 synthesis in CD4+ T lymphocytes is favored by Ag presentation by B cells and not macrophages, the precise molecular signals provided by B cells to T cells that enhance IL-4 synthesis are not clear. To examine this issue, we established an APC-independent system to activate highly purified T cells and induce cytokine synthesis, using immobilized mAbs against several T cell surface molecules, including CD3, CD28, and the CD40 ligand (CD40L). The counter-receptors for all three of these molecules are expressed on B cells, and include CD40, which is expressed primarily on B cells, but also on dendritic cells and thymic epithelium. We found that IL-4 synthesis was greatly enhanced by triggering of CD40L on the T cell surface in conjunction with ligation of CD3/TCR and CD28, whereas ligation of CD3/TCR and CD28 in the absence of CD40L triggering resulted in little or no IL-4 synthesis. CD40L costimulation greatly enhanced IL-4 synthesis both in T cells from normal nonallergic adult subjects as well as in naive T cells from cord blood. Furthermore, we demonstrated that IL-4 synthesis was optimally enhanced when the strength of the CD3/TCR signal was limiting, while IL-4 synthesis was inhibited when CD3/TCR stimulation was maximal. These studies confirm that IL-4 synthesis can be induced in normal T lymphocytes in the absence of exogenous IL-4, and demonstrate that CD40L costimulation is of fundamental importance in regulation of IL-4 production. In addition, these findings provide a mechanism by which B cells preferentially enhance IL-4 synthesis in T cells at low Ag concentrations.

Cross-linking of the CD40 ligand on human CD4+ T lymphocytes generates a costimulatory signal that up-regulates IL-4 synthesis

Although there is good evidence that the induction of IL-4 synthesis in CD4+ T lymphocytes is favored by Ag presentation by B cells and not macrophages, the precise molecular signals provided by B cells to T cells that enhance IL-4 synthesis are not clear. To examine this issue, we established an APC-independent system to activate highly purified T cells and induce cytokine synthesis, using immobilized mAbs against several T cell surface molecules, including CD3, CD28, and the CD40 ligand (CD40L). The counter-receptors for all three of these molecules are expressed on B cells, and include CD40, which is expressed primarily on B cells, but also on dendritic cells and thymic epithelium. We found that IL-4 synthesis was greatly enhanced by triggering of CD40L on the T cell surface in conjunction with ligation of CD3/TCR and CD28, whereas ligation of CD3/TCR and CD28 in the absence of CD40L triggering resulted in little or no IL-4 synthesis. CD40L costimulation greatly enhanced IL-4 synthesis both in T cells from normal nonallergic adult subjects as well as in naive T cells from cord blood. Furthermore, we demonstrated that IL-4 synthesis was optimally enhanced when the strength of the CD3/TCR signal was limiting, while IL-4 synthesis was inhibited when CD3/TCR stimulation was maximal. These studies confirm that IL-4 synthesis can be induced in normal T lymphocytes in the absence of exogenous IL-4, and demonstrate that CD40L costimulation is of fundamental importance in regulation of IL-4 production. In addition, these findings provide a mechanism by which B cells preferentially enhance IL-4 synthesis in T cells at low Ag concentrations.

IL-12 inhibits the production of IL-4 and IL-10 in allergen-specific human CD4+ T lymphocytes

IL-12 influences cytokine synthesis in unprimed CD4+ T cells by enhancing IFN-gamma synthesis and enhancing the development of Th1 cells, but its effects upon Ag-primed T cells, which are thought to have relatively fixed cytokine profiles, is less clear. We investigated the capacity of IL-12 to modify cytokine synthesis in allergen-specific human CD4+ T lymphocytes from allergic donors after in vitro stimulation. CD4+ T cells were obtained from the peripheral blood of subjects with allergic rhinitis, depleted of activated T cells, and cultured with APCs and allergen. IL-12 dramatically inhibited the development of IL-4 and IL-10 synthesis, while it enhanced T cell secretion of IFN-gamma and IL-2, and enhanced Ag-specific T cell proliferation. The inhibitory effect of IL-12 on IL-4 synthesis was not dependent on the presence of IFN-gamma, was greatest when IL-12 was added at the initiation of culture, and was minimal when added late, indicating that resting memory CD4+ T cells were more sensitive than activated CD4+ T cells to the effects of IL-12. The effect of IL-12 on IL-4 and IL-10 synthesis was not dependent on the APC type, because IL-12 decreased IL-4 synthesis when either B cells or monocytes served as APCs. These results indicate that IL-12 may be therapeutically beneficial in the treatment of allergic diseases in which allergen-specific T cells characteristically produce enhanced quantities of IL-4 and IL-10.

IL-12 inhibits the production of IL-4 and IL-10 in allergen-specific human CD4+ T lymphocytes

IL-12 influences cytokine synthesis in unprimed CD4+ T cells by enhancing IFN-gamma synthesis and enhancing the development of Th1 cells, but its effects upon Ag-primed T cells, which are thought to have relatively fixed cytokine profiles, is less clear. We investigated the capacity of IL-12 to modify cytokine synthesis in allergen-specific human CD4+ T lymphocytes from allergic donors after in vitro stimulation. CD4+ T cells were obtained from the peripheral blood of subjects with allergic rhinitis, depleted of activated T cells, and cultured with APCs and allergen. IL-12 dramatically inhibited the development of IL-4 and IL-10 synthesis, while it enhanced T cell secretion of IFN-gamma and IL-2, and enhanced Ag-specific T cell proliferation. The inhibitory effect of IL-12 on IL-4 synthesis was not dependent on the presence of IFN-gamma, was greatest when IL-12 was added at the initiation of culture, and was minimal when added late, indicating that resting memory CD4+ T cells were more sensitive than activated CD4+ T cells to the effects of IL-12. The effect of IL-12 on IL-4 and IL-10 synthesis was not dependent on the APC type, because IL-12 decreased IL-4 synthesis when either B cells or monocytes served as APCs. These results indicate that IL-12 may be therapeutically beneficial in the treatment of allergic diseases in which allergen-specific T cells characteristically produce enhanced quantities of IL-4 and IL-10.

IL-12 inhibits IL-4 synthesis in keyhole limpet hemocyanin-primed CD4+ T cells through an effect on antigen-presenting cells

Although IL-12 is known to enhance IFN-gamma synthesis in unprimed CD4+ T cells, the effect of IL-12 on IL-4 synthesis in primed CD4+ T cells, which are thought to have relatively fixed cytokine profiles, has not been clearly examined. We examined the effects of IL-12 on cytokine production by CD4+ keyhole limpet hemocyanin (KLH)-primed memory lymph node T cells and by already established KLH-specific CD4+ T cell clones. First, we found that the presence of IL-12 greatly reduced the development of IL-4 synthesis in resting but not activated memory CD4+ T cells. Although IL-12 did not inhibit the production of IL-4 in cloned Th2 effector cells, it greatly inhibited the development of IL-4 synthesis in primed CD4+ T cells taken from the lymph nodes of mice previously immunized with KLH. Secondly, we found that IL-12 inhibited IL-4 synthesis either when directly added to cultures of T cells or when APC were preincubated in IL-12. Inasmuch as the enhancing effect of IL-12 on IFN-gamma synthesis occurred optimally only when the T cells were cultured directly in IL-12, these studies indicate that IL-12 affects IL-4 synthesis via a mechanism that involves APC, a process that differs from that by which it affects IFN-gamma synthesis. These studies also indicate that the administration of IL-12 would be clinically useful in treating patients, for example those with allergic disease or lepromatous leprosy, in whom memory T cells inappropriately overproduce IL-4.

IL-12 inhibits IL-4 synthesis in keyhole limpet hemocyanin-primed CD4+ T cells through an effect on antigen-presenting cells

Although IL-12 is known to enhance IFN-gamma synthesis in unprimed CD4+ T cells, the effect of IL-12 on IL-4 synthesis in primed CD4+ T cells, which are thought to have relatively fixed cytokine profiles, has not been clearly examined. We examined the effects of IL-12 on cytokine production by CD4+ keyhole limpet hemocyanin (KLH)-primed memory lymph node T cells and by already established KLH-specific CD4+ T cell clones. First, we found that the presence of IL-12 greatly reduced the development of IL-4 synthesis in resting but not activated memory CD4+ T cells. Although IL-12 did not inhibit the production of IL-4 in cloned Th2 effector cells, it greatly inhibited the development of IL-4 synthesis in primed CD4+ T cells taken from the lymph nodes of mice previously immunized with KLH. Secondly, we found that IL-12 inhibited IL-4 synthesis either when directly added to cultures of T cells or when APC were preincubated in IL-12. Inasmuch as the enhancing effect of IL-12 on IFN-gamma synthesis occurred optimally only when the T cells were cultured directly in IL-12, these studies indicate that IL-12 affects IL-4 synthesis via a mechanism that involves APC, a process that differs from that by which it affects IFN-gamma synthesis. These studies also indicate that the administration of IL-12 would be clinically useful in treating patients, for example those with allergic disease or lepromatous leprosy, in whom memory T cells inappropriately overproduce IL-4.

Interleukin 4 production by CD4+ T cells from allergic individuals is modulated by antigen concentration and antigen-presenting cell type

We have previously shown that CD4+ T cells from allergic individuals are predisposed to produce interleukin (IL)-4 in response to allergens, and that allergen immunotherapy greatly reduced IL-4 production in an allergen-specific fashion. The mechanism that results in the reduction of IL-4 synthesis in treated individuals is unknown, but because clinical improvement during immunotherapy is associated with the administration of the highest doses of allergen, we hypothesized that high concentration of allergen results in the downregulation of IL-4 synthesis in CD4+ T cells. In this report, we demonstrated that CD4+ T cells from allergic donors produced high levels of IL-4 when stimulated with low concentrations of allergen (0.003-0.01 micrograms/ml), particularly when B cell-enriched populations presented the antigen. In contrast, the same responding CD4+ T cell population produced little IL-4 when stimulated with high concentrations of allergen (10-30 micrograms/ml), especially when monocytes were used as antigen-presenting cells (APC). The quantity of IL-4 produced was also found to be inversely related to the extent of proliferation of the CD4+ T cells in response to allergen/antigen; maximal proliferation of CD4+ T cells occurred in response to high concentrations of antigen when IL-4 production was minimal. Antigen presentation by B cell-enriched populations, instead of monocytes, induced less CD4+ T cell proliferation, but induced much greater IL-4 synthesis. Moreover, the addition of increasing numbers of APC (either B cells or monocytes) to cultures containing a constant number of responder T cells resulted in increased T cell proliferation and decreased IL-4 production. These results indicate that the circumstances under which memory T cells are activated, as well as the strength of the proliferative signal to T cells, greatly affect the quantity of IL-4 produced. Thus, our observations that the cytokine profile of allergen-specific memory CD4+ T cells can indeed be modulated by the antigen dose and APC type suggest that methods that preferentially enhance allergen uptake by monocytes and that enhance T cell proliferation will improve the clinical efficacy of immunotherapy in the treatment of allergic disease.

Regulation of the interaction between Th1 and Th2 T cell clones to provide help for antibody production in vivo

On the premise that an individual with an intact immune system has the capability to develop both cellular and antibody immune responses supported by the balance between the lymphokines secreted by T helper (Th) cells, we studied the interaction between different types of Th cell clones in vivo and the parameters that may affect this interaction. We used an adoptive transfer system in which nude or lethally irradiated mice were reconstituted with histocompatible CD4+ keyhole limpet hemocyanin (KLH)-specific T cell clones with defined lymphokine profiles. This approach allowed us to study the effects of the cognate interaction between T and B cells in the presence of a defined set of lymphokines. We demonstrated that the co-transfer of both subsets of Th cells resulted in increased production of IgA, and decreased production of IgE and IgG2a. The concomitant presence of both cell types also increases their functional survival in vivo. We have shown that in the presence of a Th2 clone, higher immunization doses (above 100 micrograms trinitrophenol (TNP)-KLH/mouse) result in increased production of IgE and IgG1. In contrast, when a Th1 clone is present, low immunization doses (less than 50 micrograms TNP-KLH/mouse) resulted in increased production of IgG2a. We were also able to show that the neutralization of interleukin-4(IL-4) and or interferon-gamma (IFN-gamma) was sufficient to abrogate most of the regulatory effects caused by the Th2 or the Th1 clone respectively. Our results indicate that the subset of T cell(s) transferred determines the type of response obtained. In addition, the data presented indicate that the antigen dose used for immunization can modulate the quantitative parameters of the response. Furthermore, we have shown that the interaction between the two subsets of T cells in vivo is characterized by both antagonistic and agonistic effects and that most of the regulatory effects exerted by one subset over the other are mediated by IL-4 or IFN-gamma.

IL-4 synthesis by in vivo-primed memory CD4+ T cells: II. Presence of IL-4 is not required for IL-4 synthesis in primed CD4+ T cells

Previous studies have shown that the presence of IL-4 is required for the development of IL-4 synthesis in naive CD4+ T cells. The purpose of our current studies was to investigate the role of IL-4 in the development of IL-4 synthesis in primed memory T cells. We therefore examined CD4+ T cells taken from lymph nodes of BALB/c mice immunized with keyhole limpet hemocyanin (KLH) and restimulated in vitro with KLH. Our results with such primed resting CD4+ T cells programmed to produce IL-4 indicated that the production of IL-4 did not require the presence of IL-4 (although the presence of IL-2 was absolutely necessary), and was only slightly limited by the presence of anti-IL-4 MAb. These results with resting memory T cells were not biased by the presence of activated T cells already producing substantial quantities of IL-4, since we demonstrated that high-density memory T cells could produce IL-4 in the absence of IL-4, and because T cells that actively produce IL-4 do not persist in vivo very long after antigen exposure. These results indicate that IL-4 synthesis in T cells committed to IL-4 production can indeed occur in the absence of IL-4 when culture conditions have been optimized and suggest that therapies with anti-IL-4 MAb or with soluble IL-4 receptors designed to control the development of IL-4 synthesis in memory T cells from individuals exhibiting excessive IL-4 synthesis will be unsuccessful. Therefore, other therapies, for example, utilizing IL-12, will be required to modulate the relatively fixed programs in memory T cells that direct the development of cytokine synthesis.

Human alveolar macrophages present antigen ineffectively due to defective expression of B7 costimulatory cell surface molecules

Alveolar macrophages, resident phagocytic cells in the lung that derive from peripheral blood monocytes, are paradoxically ineffective in presenting antigen to T cells. We found that antigen presentation by alveolar macrophages could be restored by the addition of anti-CD28 mAb to cultures of T cells and macrophages, indicating that costimulation by alveolar macrophages via the CD28 pathway was defective. In addition, we found that alveolar macrophages activated with IFN-gamma failed to express B7-1 or B7-2 antigens, which normally ligate CD28 on T cells and provide a costimulatory signal required for the activation of T cells. These observations are the first to demonstrate the inability of a "professional" antigen-presenting cell type to effectively express the costimulatory molecules B7-1 and B7-2. Inasmuch as immune reactions within the lung are inevitably associated with inflammatory injury to pulmonary tissue, these observations suggest that reduced expression of B7-1 and B7-2 by alveolar macrophages may be advantageous, as a critical mechanism involved in the induction of peripheral tolerance to the abundance of antigens to which mucosal tissues are continuously exposed.