Pertussis toxin enhanced IgG1 and IgE responses to primary tetanus immunization are mediated by interleukin-4 and persist during secondary responses to tetanus alone

Bordetella bronchiseptica is a potent and safe adjuvant that enhances the antigen-presenting capability of dendritic cells

We previously demonstrated that Bordetella bronchiseptica (B. bronchiseptica) antigen (Ag) enhances the Mycoplasma hyopneumoniae Ag-specific immune response. The focus of this study was whether acellular bacterin of B. bronchiseptica could be used as an adjuvant to increase antigen-presenting capability of dendritic cells (DCs) by increasing the level of activation. The metabolic activity of DCs was increased by B. bronchiseptica, similar to lipopolysaccharide (LPS). Flow cytometry analysis revealed that B. bronchiseptica increases the expression of major histocompatibility complex class-2, cluster of differentiation (CD)40, CD54, and CD86 which are closely related to DC-mediated immune responses. B. bronchiseptica enhanced the production of cytokines related to adaptive immune responses. Furthermore, the survival rate of B. bronchiseptica-injected groups was 100% at 15 and 20 mg/kg doses, whereas that of LPS-injected groups was only 20%, 0% at 15 and 20 mg/kg doses respectively, and so B. bronchiseptica is likely to be safer than LPS. Taken together, these results indicate that B. bronchiseptica can be used as an adjuvant to enhance the antigen-presenting capability of DCs. B. bronchiseptica is a candidate for producing vaccines, especially in case of DC-mediating efficacy and safety demands. This study provides researchers and clinicians with valuable information regarding the usage of B. bronchiseptica as a safe bacteria-derived immunostimulating agent for developing efficient vaccines.

Functional Programming of Innate Immune Cells in Response to Bordetella pertussis Infection and Vaccination

Despite widespread vaccination, B. pertussis remains one of the least controlled vaccine-preventable diseases. Although it is well known that acellular and whole cell pertussis vaccines induce distinct immune functionalities in memory cells, much less is known about the role of innate immunity in this process. In this review, we provide an overview of the known differences and similarities in innate receptors, innate immune cells and inflammatory signalling pathways induced by the pertussis vaccines either licensed or in development and compare this to primary infection with B. pertussis. Despite the crucial role of innate immunity in driving memory responses to B. pertussis, it is clear that a significant knowledge gap remains in our understanding of the early innate immune response to vaccination and infection. Such knowledge is essential to develop the next generation of pertussis vaccines with improved host defense against B. pertussis.

Investigating pertussis toxin and its impact on vaccination

Whooping cough, caused by Bordetella pertussis, remains a major global health problem. Each year around 40 million of pertussis cases resulting in 200,000-400,000 annual deaths occur worldwide. Pertussis toxin is a major virulence factor of B. pertussis. Murine studies have shown its importance in bacterial colonization and in immunomodulation to evade innate or adaptive immunity. The toxin is composed of an A protomer expressing ADP-ribosyltransferase activity and a B oligomer, responsible for toxin binding to target cells. The toxin is also a major protective antigen in all currently available vaccines. However, vaccine escape mutants with altered toxin expression have recently been isolated in countries with high vaccination coverage illustrating the need for improved pertussis vaccines.

Characterization of the key antigenic components of pertussis vaccine based on outer membrane vesicles

Pertussis has resurged during the last two decades in different countries. In particular in the 2010-2013 period large outbreaks were detected in US, Australia, UK and The Netherlands with significant mortality in infants. The epidemiological situation of pertussis points out the need to develop new vaccines and in this regard we previously developed a new vaccine based on outer membrane vesicles (OMVs) which have been shown to be safe and to induce protection in mice. Here we have further investigated the properties of OMVs vaccines; in particular we studied the contribution of pertussis toxin (PTx) and pertactin (Prn) in OMVs-mediated protection against pertussis. PTx-deficient OMVs and Prn-deficient OMVs were obtained from defective Bordetella pertussis mutants. The absence of PTx or Prn did compromise the protective capacity of the OMVs formulated as Tdap vaccine. Whereas the protective efficacy of the PTx-deficient OMVs in mice was comparable to Prn-deficient OMVs, the protective capacity of both of them was significantly impaired when it was compared with the wild type OMVs. Interestingly, using OMVs obtained from a B. pertussis strain which does not express any of the virulence factors but expresses the avirulent phenotype; we observed that the protective ability of such OMVs was lower than that of OMVs obtained from virulent B. pertussis phase. However, it was surprising that although the protective capacity of avirulent OMVs was lower, they were still protective in the used mice model. These results allow us to hypothesize that OMVs from avirulent phase shares protective components with all OMVs assayed. Using an immune proteomic strategy we identified some common components that could play an important role in protection against pertussis.

Spontaneous regression of metastatic melanoma after inoculation with tetanus-diphtheria-pertussis vaccine

Spontaneous regression of metastatic melanoma is an exceedingly rare event, with only 76 well-documented cases in the literature since 1866. Here, we present the case of a patient who developed metastatic melanoma despite interferon therapy and who then achieved spontaneous regression shortly after a reaction to tetanus-diphtheria-pertussis vaccination. A common theme among these cases is the development of febrile illness before remission of the malignant disease. A brief overview of proposed mechanisms for these miraculous recoveries is presented, including a highlight on the potential role of the herv-k-mel viral marker, a nona- or decapeptide that appears in most melanomas, with homologies to peptides in pathogenic microorganisms.

Induction of polyclonal CD8+ T cell activation and effector function by Pertussis toxin

Pertussis toxin (PTX) has pronounced adjuvant activity and strongly enhances innate and adaptive immune responses, including increased antibody production and Th1/Th2 cytokine production. Adjuvant effects of PTX on Th1 and Th2 cells are primarily mediated via CD80/86 costimulation via enhanced expression of these molecules by APCs. However, it has remained unresolved whether PTX modulates the expression of costimulatory and inhibitory molecules on CD4+ and CD8+ T cells. To address this question, we determined the expression kinetics of CD28, CTLA-4, and CD40L on spleen CD4+ and CD8+ T cells after incubation with PTX. The results show that PTX upregulated the expression of CD28 by CD8+ T cells, but not by CD4+ T cells. In contrast, the expression of CTLA-4 and CD40L was not substantially altered on CD4+ or CD8+ T cells. CD28 upregulation by CD8+ T cells was paralleled by upregulation of CD69 and the induction of IFN-γ, Granzyme B (GrB), and IL-17. CD8+ T cell activation and cytokine production could be substantially blocked with anti-CD80 and CD86 antibodies, consistent with CD28 mediated signaling. Treatment of highly purified CD8+ T cells with PTX resulted in upregulation of CD28 and CD69, and production of IFN-γ. Incubation with CD28 mAb further enhanced this effect, suggesting that PTX has direct effects on CD8+ T cells which are enhanced by CD80/86-mediated costimulation provided by APCs.

Immunotoxicity—The Risk is Real

Several papers published over the last year represent significant progress in closing the gap between rodent immunotoxicity data and human risk and indicate that, at least for the developing immune system, the concern raised by rodent data is justified. The studies reviewed here show that suppression of immune responses in rodents is predictive of suppression of immune responses in humans and that there is a relationship between immune suppression following developmental exposure to the toxicants and enhanced risk of infectious or neoplastic disease in humans. The three cases highlighted here are remarkable in that they all deal with real-world environmental exposures that represent different media -- air (cigarette smoke), water (arsenic), and food (polychlorinated biphenyls [PCBs]) -- and constitute very real risks. Moreover, the arsenic and PCB studies actually demonstrate a quantitative relationship between human exposure and immune suppression. There is evidence that in utero exposure to cigarette smoke and arsenic but not PCBs is associated with increased risk of allergic disease as well. There is clearly potential for designing studies that could address both issues.

Effects of a diphtheria-tetanus-acellular pertussis vaccine on immune responses in murine local lymph node and lung allergy models

We have previously shown that in mice, diphtheria-tetanus-acellular pertussis (DTaP) vaccination before Bordetella pertussis infection resulted in, besides effective clearance, immediate hypersensitivity (lung eosinophilia, increased total serum immunoglobulin E [IgE], and increased ex vivo Th2 cytokine production by cells from the bronchial lymph nodes). To better appreciate the extent of these findings, we measured DTaP vaccination effects in the local lymph node assay (LLNA) and an ovalbumin (OVA) lung allergy model. In the LLNA, mice were vaccinated or adjuvant treated before being sensitized with trimellitic anhydride (TMA; inducing a Th2-directed response) and dinitrochlorobenzene (DNCB; inducing a Th1-directed response). Compared to the adjuvant-treated controls, the vaccinated mice showed a decreased response to TMA and (to a much lesser extent) an increased response to DNCB. The decreased response to TMA coincided with increased transforming growth factor beta levels. With the exception of filamentous hemagglutinin, all vaccine constituents contributed to the decreased response to TMA. In the lung allergy model, sensitization induced OVA-specific IgE, lung pathology (peribronchiolitis, perivasculitis, and hypertrophy of the bronchiolar mucus cells) and increased the number of eosinophils, lymphocytes, and neutrophils in the bronchoalveolar lavage fluid. Vaccination failed to modulate these parameters. In conclusion, although DTaP vaccination may affect the LLNA response, we found no evidence of an effect on lung allergy.

Induction of dendritic cell maturation by pertussis toxin and its B subunit differentially initiate Toll-like receptor 4–dependent signal transduction pathways

OBJECTIVE

Pertussis toxin (PT) has the capacity to activate dendritic cells (DCs) for the augmentation of cell-mediated immune responses. To investigate the mechanism(s) by which PT activates DCs, we investigated the effects of PT and its B-oligomer (PTB) on the maturation of human and mouse DCs and determined whether PT could act as a pathogen-associated molecular pattern to activate one of the Toll-like receptors (TLRs).

METHODS

The effects of PT and PTB on the maturation of human and mouse DCs were analyzed in terms of surface marker expression, cytokine production, antigen-presenting capacity, and intracellular signaling. The participation of TLR4 in PT-induced signaling was determined by comparing the effect of PT on DCs derived from TLR4-deficient and wild-type mice, as well as by measuring PT-induced NF-kappaB activation in HEK293 cells transiently transfected to express various TLRs.

RESULTS

Although both promoted phenotypic and functional maturation DCs, however, unlike PT that induced DC production of interleukin (IL)-6, tumor necrosis factor-alpha, IL-12, and interferon-inducible protein, PTB was capable of stimulating the production of interferon-inducible protein. Bone marrow-derived DCs from C3H/HeJ mice with defective TLR-4 alleles were unresponsive to PT and PTB, whereas DCs from C3H/HeN mice responded. In addition, PT induced NF-kappaB activation and IL-8 production in HEK293 cells transfected with a combination of TLR4 and MD2 but not in nontransfected or TLR2-transfected HEK293 cells. Comparison of the patterns of cytokine induction and intracellular signaling events in DCs treated by PT and PTB revealed that although PT, like lipopolysaccharide, triggered both MyD88-dependent and -independent pathways, PTB preferentially triggered MyD88-independent pathways. Interestingly, mouse splenocyte proliferation in response to PT and PTB was only partially dependent on TLR4.

CONCLUSION

The data identify PT as another pathogen-associated molecular pattern that induces DC maturation in a TLR4-dependent manner. Unlike PT, which triggers both MyD88-dependent and -independent pathways, PTB only triggers the MyD88-independent pathway in DCs.

A CpG-containing oligodeoxynucleotide as an efficient adjuvant counterbalancing the Th1/Th2 immune response in diphtheria-tetanus-pertussis vaccine

Adjuvants in vaccines are immune stimulants that play an important role in the induction of effective and appropriate immune responses to vaccine component(s). Diphtheria-tetanus-pertussis (DPT) vaccine contains not only aluminum hydrate (alum) to enhance the immune response to the vaccine ingredients, but also, both for that purpose and as a principal ingredient, pertussis toxin (PT). However, both adjuvants strongly promote T helper (Th) 2 type immune responses. Th1 and Th2 type immune responses are counterbalanced in vivo, and a Th2-prone immune response is not effective against intracellular infections but promotes IgE production, which is related to allergic disease. In this study, we used the CpG motif contained in oligodeoxynucleotide (CpG-ODN), which has an adjuvant effect and also induces the Th1 response, as an adjuvant to this vaccine, and we investigated its adjuvanticity and its potential to modulate immune responses to DPT vaccine. Administration of DPT vaccine with CpG-ODN (DPT-alum/ODN) to mice significantly reduced the total IgE levels and increased the anti-PT specific IgG2a titer in serum, in comparison with ordinary DPT vaccine (DPT-alum). Moreover, we investigated the antibody response to orally administrated ovalbumin (OVA) after vaccine administration. In the DPT-alum/ODN-administered group, the OVA specific IgE production in serum greatly decreased in comparison with that in the DPT-alum-administered group. These data indicate that CpG-ODN was not useful only as an efficient vaccine adjuvant but also shifted the immune responses substantially toward Th1 and modulated the Th1/Th2 immune response in DPT vaccine. These data suggested new applications of CpG-ODN as adjuvants in DPT vaccine.

Suppression of serum antibody responses by pertussis toxin after respiratory tract colonization by Bordetella pertussis and identification of an immunodominant lipoprotein

Pertussis toxin (PT), a virulence factor secreted by Bordetella pertussis, contributes to respiratory tract infection and disease caused by this pathogen. By comparing a wild-type (WT) B. pertussis strain to a mutant strain with an in-frame deletion of the ptx genes encoding PT (DeltaPT), we recently found that the lack of PT confers a significant defect in respiratory tract colonization in mice after intranasal inoculation. In this study, we analyzed serum antibody responses in mice infected with the WT or DeltaPT strain and found that infection with the DeltaPT strain elicited greater responses to several B. pertussis antigens than did infection with the WT, despite the lower colonization level achieved by the DeltaPT strain. The same enhanced antibody response was observed after infection with a strain expressing an enzymatically inactive PT; but this response was not observed after infection with B. pertussis mutant strains lacking filamentous hemagglutinin or adenylate cyclase toxin, nor when purified PT was administered with the DeltaPT inoculum, indicating a specific role for PT activity in this immunosuppressive effect. In particular, there were consistent strong serum antibody responses to one or more low-molecular-weight antigens after infection with the DeltaPT strain. These antigens were Bvg independent, membrane localized, and also expressed by the closely related pathogens Bordetella parapertussis and Bordetella bronchiseptica. Two-dimensional gel electrophoresis and mass spectrometry were used to identify one of the immunodominant low-molecular-weight antigens as a protein with significant sequence homology to peptidoglycan-associated lipoprotein in several other gram-negative bacterial species. However, a serum antibody response to this protein alone did not protect mice against respiratory tract infection by B. pertussis.

1st class ticket to class I: protein toxins as pathfinders for antigen presentation

A number of bacterial toxins have evolved diverse strategies for crossing membrane barriers in order to reach their substrates in the mammalian cytosol. Recent studies show that this property can be exploited for the delivery of fused antigens into the major histocompatibility complex class I-restricted presentation pathway, with the goal of eliciting a specific immune response. Here we discuss the peculiarities of the trafficking pathways of a variety of toxins, and how these may allow the toxins to be used as delivery vehicles for therapeutic and diagnostic purposes.

Do early childhood immunizations influence the development of atopy and do they cause allergic reactions?

Concerns about allergic side-effects of vaccines and about a possible promotion of allergic diseases contribute to incomplete vaccination rates in childhood. This article reviews the current understanding of these issues. There is evidence that pertussis and diphtheria/tetanus antigens elicit immunoglobulin E (IgE) antibody formation as part of the immune response. In murine models, pertussis toxin is an effective adjuvant for IgE formation against simultaneously administered antigens. In children, however, sensitization to unrelated antigens or development of allergic diseases do not seem to be augmented. In contrast, bacille Calmette-Guérin (BCG) and measles vaccination have been proposed as suppressors of allergy because of their T helper 1 (Th1)-fostering properties. In the murine system, BCG inhibits allergic sensitization and airway hyper-reactivity. Some epidemiological studies in humans suggest an inhibitory effect of tuberculosis on allergy. BCG vaccination in children, however, has no or merely a marginal suppressive effect on atopy. Other vaccine components such as egg proteins, gelatin, and antibiotics are a potential hazard to children with severe clinical reactions to these allergens. These rare children should be vaccinated under special precautions. In conclusion, vaccination programs do not explain the increasing prevalence of allergic diseases, but individual children may uncommonly develop an allergic reaction to a vaccine. The risks of not vaccinating children, however, far outweigh the risk for allergy. Therefore, childhood vaccination remains an essential part of child health programs and should not be withheld, even from children predisposed for allergy.

Down-regulation of IgE and IgG4 antibodies to tetanus toxoid and diphtheria toxoid by covaccination with cellular Bordetella pertussis vaccine

Pertussis (P) toxin acts as adjuvant for IgE formation against simultaneously administered Ags in animal models. P vaccination may also have an adjuvant impact on IgE formation against coadministered diphtheria (D) and tetanus (T) Ags in humans. Sera of 103 D-T-P-immunized and 319 D-T-immunized children aged 2 years were analyzed for IgE, IgG4, and IgG to D and T (radioallergosorbent test), total IgE and IgE against common inhalant allergens (CAP radioallergosorbent test fluoroenzyme immunoassay). Fewer D-T-P- than D-T-immunized children had sera positive for T-IgE (12.6 vs 53.6%, p < 0.001), T-IgG4 (71.6 vs 89.2%, p < 0.001), D-IgE (31.0 vs 70.5%, p < 0.001), and D-IgG4 (85.2 vs 93.4%, p = 0.039). Suppression of T-IgE was not dependent on the cutoff chosen for a positive test result, but was dependent on the proportion of D-T immunizations given with P. The risk for sensitization to common environmental allergens did not differ (odds ratio 0.953, 95% confidence interval 0.815-1.114). No significant differences between D-T- and D-T-P-immunized children were found with regard to T-IgG or D-IgG. In summary, IgE and IgG4 (but not IgG) serum levels to coadministered D- and T-Ags are suppressed among P-immunized children as compared with nonimmunized children. These results suggest that the presence of a microbial product during Ag exposure can down-regulate an IgE/IgG4 response in humans.

Immunity to Bordetella pertussis

Bordetella pertussis exploits extracellular and intracellular niches in the respiratory tract and a variety of immune evasion strategies to prolong its survival in the host. This article reviews evidence of complementary roles for cellular and humoral immunity in protection. It discusses the effector mechanisms of bacterial elimination, the strategies employed by the bacteria to subvert protective immune responses and the immunological basis for systemic and neurological responses to infection and vaccination.

Formulation and characterisation of Bordetella pertussis fimbriae as novel carrier proteins for Hib conjugate vaccines

Haemophilus influenzae type b (Hib) capsular polysaccharide (polyribosylribitol phosphate, PRP) is the active component of conjugate vaccines that have proven successful in preventing invasive Hib disease. Conjugation of PRP to a protein carrier greatly improves its immunogenicity providing protection in infants and subsequent antibody maturation upon boosting. In this study, fimbriae isolated from Bordetella pertussis have been assessed as novel carrier proteins. These proteins are components of some acellular pertussis vaccines and clinical trials have indicated that fimbriae could be important protective antigens against whooping cough. Fimbriae (Fim2 and Fim3) purified from B. pertussis were dissociated in 6 M guanidine hydrochloride, pH 10.5, to produce proteins of defined size and to facilitate the production and characterisation of the conjugates. Both carbodiimide-mediated coupling and reductive amination were used to conjugate PRP to dissociated fimbriae. Efficiency of conjugation was determined by size exclusion chromatography followed by protein and polysaccharide analysis of fractionated components. Immunisation of rabbits with dissociated fimbriae-PRP conjugates (D.fim-PRP) produced high anti-fimbrial and anti-PRP IgG titres. Use of a D.fim-PRP conjugate could protect against Hib disease and may also augment protection against B. pertussis.

Bovine respiratory syncytial virus-specific IgE is associated with interleukin-2 and -4, and interferon-gamma expression in pulmonary lymph of experimentally infected calves

OBJECTIVE

To study the local immune response of calves to bovine respiratory syncytial virus (BRSV) infection with emphasis on IgE production and cytokine gene expression in pulmonary lymph.

ANIMALS

Twelve 6- to 8-week-old Holstein bull calves. Six similar control calves were mock infected to obtain control data.

PROCEDURE

Lymphatic cannulation surgery was performed on 12 calves to create a long-term thoracic lymph fistula draining to the exterior. Cannulated calves were exposed to virulent BRSV by aerosol. Lymph fluid collected daily was assayed for BRSV and isotype-specific IgE antibody, total IgG, IgA, IgM, and protein concentrations. Interleukin-4 (IL-4), interleukin-2 (IL-2), and interferon-gamma were semi-quantitated by reverse transcription-polymerase chain reaction (RT-PCR). Cell counts and fluorescence-activated cell scanner (FACSCAN) analysis of T-cell subsets were performed on lymph cells.

RESULTS

Calves had clinical signs of respiratory tract disease during days 5 to 10 after infection and shed virus. Bovine respiratory syncytial virus-specific IgE in infected calves was significantly increased over baseline on day 9 after infection. Mean virus-specific IgE concentrations strongly correlated with increases in severity of clinical disease (r = 0.903). Expression of IL-2, IL-4, and interferon-gamma was variably present in infected and control calves, with IL-4 expression most consistent during early infection.

CONCLUSIONS AND CLINICAL RELEVANCE

Infection with BRSV was associated with production of BRSV-specific IgE, and IL-4 message was commonly found in lymph cells of infected calves. This finding supports the concept that BRSV-induced pathophysiology involves a T helper cell type-2 response. Effective therapeutic and prophylactic strategies could, therefore, be developed using immunomodulation to shift the immune response more toward a T helper cell type-1 response.

Effect of acellular pertussis vaccine on the development of allergic sensitization to environmental allergens in adults

BACKGROUND

Exposure of children to pertussis antigens caused by infection or vaccination with whole-cell pertussis vaccine may increase the serum IgE level and predispose to sensitization to the prevalent environmental allergens. Acellular pertussis vaccine (APV) that may be given to adults may have a similar effect.

OBJECTIVE

The purpose of this study was to determine whether APV will cause an increase in environmental sensitization measured by an increase of serum-specific IgE to the allergens to which adults are exposed during the vaccination period.

METHODS

One hundred adult hospital employees were randomized to receive either a 2-component APV composed of pertussis toxin and filamentous hemagglutinin or a meningococcal vaccine as a control. Serum-specific IgE level to 2 indoor allergens, cat and dust mite, and 2 outdoor allergens prevalent during the immunization season, Alternaria species and ragweed, was measured by an RIA on sera collected before and 1 month after vaccination.

RESULTS

The group that received the APV had no significant change in their serum-specific IgE levels to cat, dust, Alternaria species, or ragweed 1 month after vaccination.

CONCLUSION

A 2-component APV did not predispose to an increase of allergen-specific IgE in an adult population.

Adjuvant and protective properties of native and recombinant Bordetella pertussis adenylate cyclase toxin preparations in mice

Bordetella pertussis produces a cell-invasive adenylate cyclase toxin which is synthesised from the cyaA gene as an inactive protoxin that is post-translationally activated by the product of the cyaC gene. Purified active and inactive CyaA proteins were prepared from B. pertussis or from recombinant Escherichia coli expressing both cyaA and cyaC genes or the cyaA gene alone. respectively. In addition, a hybrid toxin (Hyb2) in which an internal region of CyaA had been replaced with the analogous region from the leukotoxin (LktA) of Pasteurella haemolytica, and which had low cell-invasive activity, was also prepared from E. coli expressing the cyaC gene. The CyaA preparations showed no evidence of toxicity in a mouse weight-gain test. Active toxin preparations were protective in mice against intranasal challenge with wild-type B. pertussis, as evidenced by lung:body weight ratios and bacterial numbers in the lungs, which were comparable to those in mice given whole-cell DPT vaccine. Hyb2 was not as protective as active CyaA and inactive CyaA preparations were not protective. Active CyaA, when co-administered with ovalbumin (OA), had a marked adjuvant effect on the anti-OA IgG antibody response which was not as apparent with inactive CyaA preparations. Similarly, active CyaA stimulated a greater anti-CyaA response than the inactive form.

Administration of interleukin-12 prevents mite Der p 1 allergen-IgE antibody production and airway eosinophil infiltration in an animal model of airway inflammation

The aim of the present study was to examine the in vivo effect of interleukin (IL)-12 on a murine model of asthma induced by Dermatophagoides pteronyssinus-derived Der p 1 allergen. C57BL/6 mice immunized with Der p 1 allergen adsorbed to alum/pertussis toxin developed a T-helper type 2 (Th2)-dominant immune response characterized by the presence of IgE antibody, airway eosinophil infiltration and increased production of Th2 cytokine. Intraperitoneal injection of IL-12 (1 or 0.1 microg per day) for 5 days (day -1 to +3) simultaneously with each immunization, inhibited the production of IgE and IgG1 antigen-specific antibodies, whereas production of IgG2a was strongly enhanced. In addition, mice receiving both doses of IL-12 showed a strong inhibition of IL-5 but up-regulation of IFN-gamma production by spleen cells stimulated with antigen. Administration of IL-12 also prevented antigen-induced eosinophil infiltration into the bronchoalveolar area in a dose-dependent manner and the primary inflammatory mediator serotonin in bronchoalveolar lavage (BAL) fluids was also reduced significantly. Taken together, the data indicate that IL-12 has a potent immunomodulatory effect on house-dust-mite-induced allergic disorders and may be used as an efficient agent for immunotherapy.