The inverse association between tuberculin responses and atopic disorder

Reciprocal age-related patterns of allergen-specific T-cell immunity in normal vs. atopic infants

By adulthood there is almost universal immunological memory to aeroallergens, and the presence of allergic disease appears to be related to the nature of the underlying T-helper (Th) cell cytokine responses. The hypothesis of this study is that adult patterns of allergen specific Th-cell memory (Th-2 polarized in atopics vs. Th1 in non-atopics) can be determined in early infancy. Mononuclear cell cytokine responses to house-dust mite were measured at 6-monthly intervals from birth to 2 years of age, using ELISA (IL-10, IL-13, IFN-gamma) and sqRT/PCR (IL-4, IL-5, IL-9, IFN-gamma) in normal infants (n = 14) with no family history or allergic symptoms, and infants with a family history and definite atopy by 2 years (n = 16). Both normals and atopics showed low-level Th2 skewed allergen-specific responses at birth with little accompanying IFN-gamma. The Th2 responses to house-dust mite were higher in normal newborns, who then show a rapid downregulation of these responses in the first year of life. Atopic infants instead show a consolidation of their neonatal patterns of Th2 polarized allergen specific immunity. Earlier studies indicate that neonates at high risk of atopy display diminished capacity for production of the Th1 cytokine IFN-gamma. The present study suggests for the first time that neonates who subsequently develop atopy also initially have reduced capacity to mount Th2 responses. However, in contrast to non-atopics who selectively downregulate their fetal Th2 polarized allergen-specific responses, atopic children display age-associated upregulation of Th2 immunity.

Early childhood infection and atopic disorder

BACKGROUND

Atopy is of complex origins but the recent rise in atopic diseases in westernized communities points to the action of important environmental effects. One candidate mechanism is the changing pattern of microbial exposure in childhood. This epidemiological study investigated the relationship between childhood infections and subsequent atopic disease, taking into account a range of social and medical variables.

METHODS

A total of 1934 subjects representing a retrospective 1975-84 birth group at a family doctor practice in Oxfordshire were studied. Public health and practice records were reviewed; temporal records were made of all diagnoses of infections and their treatments, all immunisations, and diagnoses of asthma, hay fever and eczema; maternal atopy and a number of other variables were documented.

RESULTS

Logistic regression analysis identified three statistically significant predictors of subsequent atopic disease: maternal atopy (1.97, 95% CI 1.46 to 2.66, p < 0.0001), immunisation with whole-cell pertussis vaccine (1.76, 95% CI 1.39 to 2.23, p < 0.0001), and treatment with oral antibiotics in the first two years of life (2.07, 95% CI 1.64 to 2.60, p < 0.0001). There was no significant association found for maternal smoking, bottle feeding, sibship size, or social class.

CONCLUSIONS

The prediction of atopic disease by maternal atopy mainly reflects the effect of acknowledged genetic factors. Interpretation of the prediction of atopic disorders by immunisation with wholecell pertussis vaccine and treatment with oral antibiotics needs to be very cautious because of the possibilities of confounding effects and reverse causation. However, plausible immune mechanisms are identifiable for the promotion of atopic disorders by both factors and further investigation of these association is warranted.

Immunoregulatory networks in asthma

It is now well established that a subset of T-cell-derived cytokines (termed Th2 cytokines) programme the timing and characteristics of atopic airway disease including mast-cell sensitization, eosinophil and lymphocyte infiltration and recently mucus secretion. To date, attempts to devise ways to selectively limit the activities of Th2 cytokine-producing cells have been frustrated. However, the recent identification of the molecules which direct the activation and maturation of T cells has led to some successful attempts to block the activities of Th2 cells in models of atopic airway inflammation. Some of the agents with the most potential include antagonists of the T-cell costimulatory molecule CD28, local stimulators of the Thl subset of cytokines such as the BCG vaccine and potentially, antagonists of the eotaxin chemokine receptor and agonists of the T-cell costimulatory molecule CTLA-4. Not only do such agonists and antagonists represent potential new therapies, they could represent a rich hunting ground for those who aim to determine the ways in which atopic airway disease can be diagnosed and understood.

Hypothesis: decreased use of pediatric aspirin has contributed to the increasing prevalence of childhood asthma

BACKGROUND

The prevalence of asthma, atopic eczema, and allergic rhinitis has increased over the last three decades in Western countries. Speculation on the causes of this trend have focused on changes in environmental factors. We hypothesize that the decreased use of aspirin in favor of acetaminophen, due to the association of aspirin with Reye's syndrome during febrile respiratory infections, may be contributing to these trends in the United States.

DATA SOURCES

A detailed literature search was conducted utilizing Medline. Studies considered relevant and important involving both humans and animals in English language were used.

HYPOTHESIS

In the United States, the documented prevalence of childhood asthma has increased since 1970, but the rate of this increase accelerated upward beginning in the early 1980s when the use of pediatric aspirin decreased. During the resolution of common respiratory viral infections, prostaglandin E2 (PGE2) is produced through the actions of cyclooxygenase-2 (COX-2). Aspirin, but not acetaminophen, inhibits COX-2 activity. As PGE2 promotes TH2 and inhibits THI type cytokine generation, we hypothesize that the decreased use of aspirin may be a factor in facilitating allergic sensitization and asthma by augmenting the relative TH1/TH2 cytokine imbalance in genetically predisposed children.

CONCLUSION

We have presented an hypothesis based upon epidemiologic trends, known biologic effects of cytokines and PGE2 on allergic sensitization, and a potentially relevant pharmacologic effect of aspirin to explain a component of the increasing prevalence of childhood asthma in the United States. We suggest this theory be examined further in animal models as well as in other countries where the prevalence of childhood asthma is increasing.

Future directions for allergen immunotherapy

Over the last 30 years several approaches to modify immunotherapy have been tested, including allergoids, alum precipitation, and most recently peptides. However, none of these have replaced the traditional regimens. Over the same period our scientific understanding of allergic disease has been transformed. Today it is possible to identify and monitor changes occurring during treatment and to target many different aspects of the immune system. Recombinant technology provides a powerful technique both for sequencing proteins and producing allergens in commercial quantities. The recombinant proteins can be modified by site-directed mutagenesis so as to decrease their reactivity with IgE antibodies while maintaining reactivity with T cells. Knowledge of the tertiary structure of allergens will make it simpler to identify and change surface epitopes. A completely different approach is to use plasmids to introduce the genes for an allergen. The strength of this technique is that the plasmid can be designed to control expression and also to influence the cytokine profile of the response or the isotype of antibodies produced. Finally, different adjuvants can be used with proteins to alter the response. These include IL-12, immunostimulatory sequences of DNA, and bacterial proteins such as those used in HibVax. It is now possible to identify the cells that control the immune response to allergens and to design treatments that will either downregulate or change the response of T cells. The challenge is to transform this information into an effective treatment for allergic disease.

Prevalence of childhood asthma in the tropics

There is evidence that until quite recently asthma was infrequent in tropical developing countries. Estimates of the current and lifetime prevalence of wheeze and asthma in children in tropical countries in the 1990s suggest that the problem is increasing. There is also evidence that urbanization in tropical areas is associated with a higher prevalence of exercise-induced bronchospasm. Possible contributors to this changing pattern of asthma are discussed. These probably relate to differential exposure to house dust mite and infectious agents in infancy. There is little research on this increasing problem but it is needed in order to find ways to arrest increases in asthma.

Human macrophages induced in vitro by macrophage colony-stimulating factor are deficient in IL-12 production

IL-12 is important for Th1 differentiation. Myeloid-derived antigen-presenting cells (APC) such as monocytes, macrophages (Mphi) and dendritic cells (DC) are believed to be major sources of IL-12 in vivo. We have compared IL-12 production of fresh monocytes with Mphi differentiated in vitro using macrophage colony-stimulating factor (M-CSF) or human plasma, and in vitro generated dendritic cells, since these differentiated cell types represent APC at sites of antigen challenge. Macrophages stimulated with lipopolysaccharide (LPS) or heat-killed Listeria monocytogenes in the presence or absence of IFN-gamma produced minimal IL-12 p70 by comparison with DC or monocytes, despite comparable production of TNF-alpha. M-CSF-induced Mphi produced low levels of IL-10 constitutively and high levels after stimulation with LPS, but neutralization of IL-10 did not augment Mphi IL-12 production. Exposure of Mphi to TNF-alpha, granulocyte-macrophage CSF or IFN-gamma did not substantially up-regulate IL-12. Therefore M-CSF induces a differentiated Mphi phenotype in which IL-12 production is down-regulated, perhaps irreversibly. This may be the default pathway for monocyte-Mphi development in the absence of inflammation.

The natural history of respiratory symptoms in a cohort of adolescents

A cohort of 2,289 children, previously studied at the age of 6-8 yr, were followed up by means of a postal questionnaire when aged 14 -16 yr to examine the association between potential risk factors and the natural history of respiratory symptoms. Children with current symptoms, persistent symptoms, and late-onset symptoms were identified and multivariate analyses were performed to determine the independent association between risk factors and these various symptom-based subgroups. Personal and family history of atopy was significantly associated with all symptom groups and with the presence of doctor-diagnosed asthma. Smoking, either active or passive, was shown to be significantly associated with current, persistent, and late-onset symptoms. Other factors shown to be significantly associated with certain symptom groups were gender (late-onset wheeze), single-parent households (current cough, persistent cough), social class (late-onset wheeze), number of children in the household (persistent wheeze, late-onset cough), number of furry pets in the household (current wheeze), birth weight (late-onset wheeze), and gas cookers (current wheeze, persistent wheeze). In a subgroup of children studied in more detail in 1987, bronchial hyperresponsiveness in 1987 was positively associated with persistent wheeze in 1995, whereas positive skin-prick testing in 1987 was not.

From "magic bullet" to "specially engineered shotgun loads": the new genetics and the need for individualized pharmacotherapy

Steady progress in the identification of human pharmacogenetic variants and new discoveries of disease susceptibility genes makes the old notion of one disease/one drug untenable. Advances in the ability to rapidly identify these variants, when coupled with appropriate drug delivery systems, should revolutionize pharmacotherapy.

The association between serum levels of Th cytokines and rhinoconjunctivitis caused by methyltetrahydrophthalic anhydride

BACKGROUND

There are few epidemiologic studies on the association between serum levels of T helper (Th) cytokines and allergic symptoms caused by sensitizing agents.

METHODS

A population of 147 workers from two condenser plants using epoxy resin with methyltetrahydrophthalic anhydride (MTHPA) underwent a questionnaire survey and serologic investigations. Total and MTHPA-specific IgE levels were measured by the Pharmacia CAP System, and serum levels of interleukin (IL)-4, IL-13, and interferon-gamma (IFN-gamma) by enzyme immunoassay.

RESULTS

A significant association was found between work-related eye and nasal symptoms and a range of atopic characteristics, including the frequency of positive specific IgE, specific and total IgE levels, and IL-4 levels. A positive correlation was observed between levels of IL-4 and IL-13 (r=0.42). Furthermore, multiple logistic analysis revealed significant contributions of specific IgE and IL-13 to the work-related symptoms. A similar but nonsignificant association was also found for IL-4 (P=0.07). On the other hand, a multiple regression model with specific IgE levels as a dependent variable showed a significant association with total IgE, but not with IL-4, IL-13, and IFN-gamma.

CONCLUSIONS

These results suggest that work-related eye and nasal symptoms are closely related to specific IgE antibodies, and that allergic responses, mediated by IgE, to MTHPA may lead to a shift in the balance between Th1 and Th2 cells.

Prevalence of allergic rhinitis and atopic dermatitis among children in four regions of Finland

The primary aim of the study was to evaluate the prevalences of allergic rhinitis and atopic dermatitis and their regional differences among Finnish children. The secondary objective was to determine whether the responses to the questions used are affected by the pollen season if asked during such a season. In 1994-5, the self-reported prevalence of allergic symptoms in four regions of Finland was studied among 11,607 schoolchildren aged 13-14 years, as part of the International Study of Asthma and Allergies in Childhood (ISAAC). The prevalence of rhinoconjunctivitis during the preceding year was 16% in eastern Finland (Kuopio County, n=2821), 23% in southern Finland (Helsinki area, n=2771), 15% in southwestern Finland (Turku and Pori County, n=2983), and 16% in northern Finland (Lapland, n=3032). The respective prevalences of flexural dermatitis were 15%, 19%, 16%, and 18%. The surveys were performed in winter, except in the Helsinki area where the survey was carried out mainly in the spring pollen season. Among the children studied in autumn in Helsinki, the prevalence of rhinoconjunctivitis was 19% and that of flexural dermatitis 17%. In multivariate analysis, flexural dermatitis was slightly more common in Lapland than in all other areas. In contrast, no significant differences were found in rhinoconjunctivitis. The prevalences of both disorders were twice as high in girls as in boys. In conclusion, regional differences in the prevalence of allergic rhinitis and atopic dermatitis were small in our country, and the prevalence figures were rather similar to those reported from other European countries. Almost half of the children had suffered from at least one atopic disorder, and over one-third had had symptoms in the past year. A clear season-of-response effect was observed; the prevalence of rhinoconjunctivitis was 25% when studied during the pollen seasons in the Helsinki area.

Bacterial DNA as an evolutionary conserved ligand signalling danger of infection to immune cells

During infection, the innate limb of the immune system senses danger (pathogens) via constitutively expressed pattern-recognition receptors, and responds with activation and secretion of pro-inflammatory cytokines. Cell-wall components of gram-positive and gram-negative bacteria, such as peptidoglycan, endotoxin or lipoteichoic acid, activate via CD14, a prototypic pattern-recognition receptor for carbohydrates. This review article focuses on an alternative recognition system of the innate immune system for the recognition of bacterial DNA. Bacterial DNA differs from eukaryotic DNA in its frequency of the dinucleotides CG and its lack of methylation. These structural differences appear to be sensed by cells of the innate immune system such as antigen-presenting cells. As a consequence bacterial DNA serves as an alternate ligand to signal danger of infection. Bacterial DNA and (synthetic) oligonucleotides (ODN) derived thereof are as efficient as endotoxin in activating macrophages and dendritic cells and in triggering release of pro-inflammatory cytokines. In mice sensitized with D-galactosamine (D-GalN), high doses of bacterial DNA from either gram-positive or gram-negative pathogens induce a lethal cytokine syndrome (lethal shock). Therefore, bacterial DNA may represent a hitherto unrecognized pathophysiological entity in host-parasite interactions. Moreover, recent evidence suggests that bacterial DNA or immunostimulating ODN triggers the immunostimulation of antigen-presenting cells, and can be utilized as adjuvant to enhance immune responses of the adaptive immune system towards poorly immunogenic antigens. In fact, foreign DNA might be useful as immunotherapeutically active adjuvant to direct adaptive immune responses towards Thl-dominated immune reactions. If these findings are operative in humans, immunostimulating ODN might be used to influence Th2-dominated diseases such as allergy.

The interleukin-12/interleukin-12-receptor system: role in normal and pathologic immune responses

Interleukin-12 (IL-12) is a heterodimeric cytokine that plays a central role in promoting type 1 T helper cell (Th1) responses and, hence, cell-mediated immunity. Its activities are mediated through a high-affinity receptor composed of two subunits, designated beta 1 and beta 2. Of these two subunits, beta 2 is more restricted in its distribution, and regulation of its expression is likely a central mechanism by which IL-12 responsiveness is controlled. Studies with neutralizing anti-IL-12 antibodies and IL-12-deficient mice have suggested that endogenous IL-12 plays an important role in the normal host defense against infection by a variety of intracellular pathogens. However, IL-12 appears also to play a central role in the genesis of some forms of immunopathology. Inhibition of IL-12 synthesis or activity may be beneficial in diseases associated with pathologic Th1 responses, such as multiple sclerosis or Crohn's disease. On the other hand, administration of recombinant IL-12 may have utility in the treatment of diseases associated with pathologic Th2 responses such as allergic disorders and asthma.

Transplacental Priming of the Human Immune System to Environmental Allergens: Universal Skewing of Initial T Cell Responses Toward the Th2 Cytokine Profile

The expression of Th2-skewed immunity against soluble protein Ags present in the normal environment is recognized as the primary cause of allergic inflammation in atopics. In contrast, nonallergic normal individuals display low level Th1-skewed immunity against the same Ags (“allergens”), which is perceived as conferring protection against Th2-dependent allergic sensitization. The type of T cell memory that develops against these Ags is currently believed to be the result of complex interactions between environmental and genetic susceptibility factors, which occur postnatally when the naive immune system directly confronts the outside environment. The results of the present study challenge this general concept. We demonstrate here for the first time that Th2-skewed responses to common environmental allergens, comprising IL-4, IL-5, IL-6, IL-9, and IL-13, are present in virtually all newborn infants and are dominated by high level production of IL-10. Moreover, these responses are demonstrable within 24 h of culture initiation, arguing against a significant contribution from covert in vitro T cell priming and/or differentiation. These findings imply that the key etiologic factor in atopic disease may not be the initial acquisition of allergen-specific Th2-skewed immunity per se, but instead may be the efficiency of immune deviation mechanisms, which in normal (nonatopic) individuals redirect these fetal immune responses toward the Th1 cytokine phenotype.

The restraint stress drives a shift in Th1/Th2 balance toward Th2-dominant immunity in mice

When mice were physically restrained in 50-ml tubes for 24 h, a marked decrease of NK activity was demonstrated in parallel with the elevation of serum corticosterone levels. The release of mice from restraint stress resulted in the recovery of NK activity, with a decrease of serum corticosterone levels within 48 h. Using this stress model, we also investigated the influence of restraint stress on mouse Th1/Th2 balance. Consistent with the decrease of NK activity, IFN-gamma production of mouse spleen cells greatly reduced after suffering from restraint stress. In contrast, the IL-4 producing ability of spleen cells was not so much affected by restraint stress. These results initially indicated that stress may induce the skewing of the Th1/Th2 balance toward Th2-dominant immunity, which stimulates the occurrence of infectious diseases and allergic disorders.

Mutual antagonism of rheumatoid arthritis and hay fever; a role for type 1/type 2 T cell balance

OBJECTIVES

The balance between interferon gamma (IFN gamma) and interleukin 4 (IL4) producing T cells (T1 and T2 cells) seems to be of importance in many (auto)immune disorders. In general, T1 cell activity is important in cellular immunity whereas T2 cell activity plays a part in humoral responses. T1 cell activity predominates in joints of patients with rheumatoid arthritis (RA) whereas T2 cell activity is characteristic of atopic syndromes. This study investigated whether the prevalence of hay fever in RA is low and if severity of RA (T1 cell activity) can be influenced by the concomitant occurrence of a T2 cell mediated disease (hay fever).

METHODS

The prevalence of hay fever was assessed in 643 consecutive (RA and non-RA) patients seen in our outpatient clinic and confirmed by skin test and specific IgE. Of this group the 12 RA patients with hay fever were compared with RA patients without hay fever (matched for age, sex, and disease duration).

RESULTS

The prevalence of hay fever in RA patients is lower than in non-RA patients (4% versus 8%), and yields a relative risk for RA patients to develop hay fever of 0.48. RA patients with hay fever showed a lower disease activity (erythrocyte sedimentation rate, C reactive protein, Thompson joint score, and radiographic joint damage (Sharp) score) than RA patients without hay fever. The clinical data were related to peripheral blood T1/T2 cell balance: a lower IFN gamma/IL4 ratio was observed for RA patients with hay fever, indicating a comparatively increased T2 cell activity in RA patients with hay fever.

CONCLUSION

These results argue in favour of the exploration of treatments aimed at regulation of a possible imbalance in T1/T2 cell activity in RA.

Regulation of immune responses at mucosal surfaces: allergic respiratory disease as a paradigm

The epithelial surfaces of the respiratory tract represent a fragile interface between the immune system and the outside environment. In order to maintain local homeostasis, the adaptive immune system must continuously discriminate between innocuous antigens which are ubiquitous in the atmosphere, and antigens associated with microbial pathogens. Any breakdown in this discrimination process can potentially lead to chronic inflammatory disease. The mechanisms employed by the mucosal immune system to maintain this delicate balance are many and varied, and a comprehensive understanding of how they collectively operate would provide novel insight into a wide variety of diseases. This discussion reviews recent progress in this area, focusing on allergic respiratory disease as a model for the study of immune regulation at mucosal surfaces.

Sibship size, birth order, and atopy in 11,371 Italian young men

BACKGROUND

Having a low number of siblings and a low birth order has been reported to be a relevant risk factor for development of atopic diseases and skin sensitization to common inhalants. Although the inverse association of atopy with sibship size has been confirmed repeatedly, the association with birth order has provided conflicting results. This possibly is due to the relatively small size of the population sample examined.

OBJECTIVE

The objective of this study was to investigate the relation between sibship size, birth order, and atopy in a very large population sample, highly homogeneous for age and sex.

METHODS

This was a retrospective survey of 11,371 Italian young men, 18 to 24 years old, all candidates for enrollment in the Italian Air Force. Demographic data had been collected by a standard questionnaire. Specific IgE for locally relevant airborne allergens had been tested by a multi-RAST assay (CAP-Phadiatop).

RESULTS

The prevalence of atopy (defined as a high level of specific IgE against inhalants [cut-point >1.2 log RU]) was inversely related to the total number of siblings (25% in those with no siblings and 9% in those with five or more siblings), with a mean of a 3% decrease in prevalence for each added sibling. This relation persisted after adjustment for relevant variables such as father's education and rural and southern residence. An independent association between birth order and atopy was also observed because the decrease in atopy prevalence with increasing numbers of older siblings was significantly steeper than that found with the number of younger siblings (chi2 = 179, df = 1, p < 0.0001).

CONCLUSIONS

In a very large and homogeneous population sample of a Mediterranean country, not only sibship size but also birth order was significantly associated with atopy. This observation further highlights the role of family structure in the development of atopy and supports the hypothesis that cross-infections acquired early in infancy or in later childhood might prevent development of atopy later in life.

CTLA4Ig inhibits airway eosinophilia and hyperresponsiveness by regulating the development of Th1/Th2 subsets in a murine model of asthma

Complete T-cell activation requires two distinct signals, one delivered via the T-cell receptor, and the second "co-stimulatory" signal through CD28/B7 ligation. Previous studies showed that the blockade of CD28/B7 ligation alters differentiation of Th1/Th2 lymphocyte subsets in vitro and in vivo. The present study was designed to determine the effect of a CD28/B7 antagonist (CTLA4Ig) on Th1/Th2 development in Schistosoma mansoni-sensitized and airway-challenged mice. Treatment of mice with CTLA4Ig beginning 1 wk after sensitization abolished airway responsiveness to intravenous methacholine determined 96 h following antigen challenge. We also found a significant reduction in bronchoalveolar lavage (BAL) eosinophilia, and reduced peribronchial eosinophilic infiltration and mucoid-cell hyperplasia. Furthermore, CTLA4Ig treatment significantly decreased interleukin (IL)-4 and IL-5 content in BAL fluid in vivo, and the production of IL-5 by lung lymphocytes stimulated with soluble egg antigen (SEA) in vitro. In contrast, the content of interferon-gamma in BAL fluid and supernatant from SEA-stimulated lung lymphocytes from CTLA4Ig-treated mice was increased significantly compared with untreated animals. Thus, CTLA4Ig inhibits eosinophilic airway inflammation and airway hyperresponsiveness in S. mansoni-sensitized and airway-challenged mice, most likely due to attenuated secretion of Th2-type cytokines and increased secretion of Th1-type cytokines.

Cutting Edge: Modulation of Airway Inflammation by CpG Oligodeoxynucleotides in a Murine Model of Asthma

Asthma has been increasing in industrialized countries. Evidence suggests that asthma is caused by a Th2 immune response to inhaled environmental Ags and that childhood infections protect against this. We have shown that bacterial DNA contains motifs, centered on unmethylated CpG dinucleotides, which induce Th1-type responses. We hypothesized that the Th1 effect of these CpG motifs may oppose the Th2 type allergic response and suggest that this may account for the protective effect of childhood infection against asthma. We examined the effects of CpG-motif oligodeoxynucleotides (CpG ODN) in a murine model of asthma. Airway eosinophilia, Th2 cytokine induction, IgE production, and bronchial hyperreactivity were prevented by coadministration of CpG ODN with the Ag. Significantly, in a previously sensitized mouse, CpG ODN can prevent allergen-induced airway inflammation. These studies suggest that exposure to CpG DNA may protect against asthma.

Inhibition of an established allergic response to ovalbumin in BALB/c mice by killed Mycobacterium vaccae

Allergic disorders are mediated by T lymphocytes secreting T helper 2 (Th2) cytokines, interleukin-4 (IL-4) and interleukin-5 (IL-5), resulting in high levels of serum immunoglobulin E (IgE) and recruitment of eosinophils. One of the treatment strategies is to downregulate the Th2 component by inducing a T helper 1 (Th1) response to the relevant allergen, because Th1 and Th2 cytokines are thought to be mutually antagonistic. In this study, we examined the effects of Mycobacterium vaccae, a potent inducer of Th1 immunity, on allergic responses in a murine model. A single injection of M. vaccae into ovalbumin (OVA)-preimmunized BALB/c mice suppressed serum IgE over a wide dose range (10(7), 10(8) or 10(9) M. vaccae). Further experiments, using 10(7) M. vaccae injected twice, showed that this treatment inhibited not only serum IgE, but also the potential for ovalbumin-induced IL-5 production by spleen cells. This non-specific ability of a mycobacterium to decrease Th2 activity, even when not presented together with the allergen, is in agreement with recent epidemiological studies on the impact of bacillus Calmette-Guérin (BCG) vaccination, and of other potent Th1 stimuli, on the incidence of atopy. The suppression of serum IgE and allergen-specific IL-5 synthesis by M. vaccae suggest that this organism is likely to have clinical application in the immunotherapy of allergy.

Prevalence of allergy in children in relation to prior BCG vaccination and infection with atypical mycobacteria

By influence on the Th1/Th2 cell balance, infectious agents may affect the development of atopic allergy. In this study, we investigated whether previous BCG vaccination or infection with atypical mycobacteria might be related to the development of atopic disease. The study, which involved skin testing with mycobacteria and answers to a questionnaire for more than 6000 children in Sweden, revealed a low prevalence of allergy among BCG-vaccinated children who were immigrants or adopted from other countries. Vaccinated children born in Sweden, however, did not have significantly lower allergy prevalence than age-matched, unvaccinated children. Furthermore, the overall frequencies of skin-test reactivity to the atypical mycobacteria M. avium and M. scrofulaceum were higher rather than lower in allergic than in nonallergic children. By contrast, there was a tendency toward a lower frequency of more strongly positive skin reactions (> or = 10 mm) to mycobacteria in allergic than in nonallergic children. These findings do not support the hypothesis that early mycobacterial infections have a suppressive effect on the development of atopic disease. Earlier findings of an apparent association between atopy and lack of previous mycobacterial infection may possibly be explained by a relatively decreased ability of atopic patients to mount strong Th1 cell-mediated immune responses.

Molecular basis of allergic diseases

This review examines our current understanding of the mechanisms underlying allergic diseases. The IgE molecule plays a central role in the pathogenesis of immediate hypersensitivity reactions by virtue of its capacity to bind specifically to high-affinity IgE receptors on mast cells and mediate the release of various mast cell-derived mediators and proinflammatory cytokines on exposure to allergen. Clinically significant allergic responses are followed by a late-phase response dominated by eosinophils and T lymphocytes. The majority of T cells in allergic responses are memory T cells secreting helper type 2 (TH2)-like cytokines, i.e., interleukin (IL)-4, IL-5, IL-13, but not interferon-gamma. These cytokines regulate IgE synthesis and promote eosinophil development, thus contributing to allergic inflammatory responses. Failure to control immune activation early in the course of allergic disease blunts responses to glucocorticoid therapy and contributes to disease progression. The identification of key cells and molecules involved in the initiation and maintenance of allergic inflammation is likely to become an important target in the treatment of this common group of illnesses.

Infection of mice with Mycobacterium bovis-Bacillus Calmette-Guérin (BCG) suppresses allergen-induced airway eosinophilia

It has been proposed that the increase in prevalence and severity of atopic disorders inversely correlates with exposure to infectious diseases such as tuberculosis. We have investigated this issue by combining an intranasal Mycobacterium bovis-Bacillus Calmette-Guérin (BCG) infection with a murine model of allergen, (ovalbumin [OVA]) induced airway eosinophilia. BCG infection either 4 or 12 wk before allergen airway challenge resulted in a 90-95 and 60-70% reduction in eosinophilia within the lungs, respectively, compared to uninfected controls. The inhibition of airway eosinophilia correlated with a reduced level of IL-5 production by T cells from the lymph node draining the site of OVA challenge. Interestingly, BCG infection of the lung had no effect on IgG1 and IgE OVA-specific serum immunoglobulin or blood eosinophil levels. Furthermore, BCG-induced inhibition of airway eosinophilia was strongly reduced in interferon (IFN)-gamma receptor-deficient mice and could be partially reversed by intranasal IL-5 application. Intranasal BCG infections could also reduce the degree of lung eosinophilia and IL-5 produced by T cells after Nippostrongylus brasiliensis infection. Taken together, our data suggest that IFN-gamma produced during the T helper cell (Th)1 immune response against BCG suppresses the development of local inflammatory Th2 responses in the lung. Most importantly, this inhibition did not extend to the systemic immunoglobulin response against OVA. Our data support the view that mycobacterial infections have the potential to suppress the development of atopic disorders in humans.

Mucosal IL-12 gene delivery inhibits allergic airways disease and restores local antiviral immunity

Allergic asthma strongly correlates with airways inflammation driven by interleukin (IL)-4 and IL-5 secreted by allergen-specific CD4+ T cells. It is possible that over-production of these factors in the lungs may render asthmatic individuals less able to resolve virus infection of the respiratory tract by down-regulating type 1 cytokine-driven immune responses. IL-12 is important for the establishment of cell-mediated immunity (CMI) and may also inhibit responses driven by type 2 cytokine production. Sustained expression of IL-12 in the airways may, therefore, represent an effective preventive treatment or therapy for allergic asthma and any adverse consequences of excessive production of type 2 cytokines for the development of local CMI. Here, we show that allergic responses in airways profoundly inhibit the development of antiviral CMI in mice following local immunization with vaccinia virus (VV) leading to persistent lung infection. However, mucosal gene transfer of IL-12 in the lung, via a VV vector, inhibited local type 2 cytokine production, both prevented the development of allergic disease and airways hyperreactivity in a manner largely dependent on endogenous interferon-gamma expression and suppressed established allergic disease, and reversed the suppression of local antiviral CMI responses resulting in rapid resolution of virus infection. Our study provides the first direct demonstration that allergic conditions, particularly in airways, may inhibit immune responses to concomitant virus infection and suggests that transient mucosal IL-12 gene therapy represents an effective approach to both the prevention and treatment of allergic airways disease and associated immunosuppression of CMI.

Family size, childhood infections and atopic diseases. The Aberdeen WHEASE Group

BACKGROUND

This study addresses the causes of the increases in childhood asthma and allergic disease. On the basis of an observed inverse relationship between family size and allergic disease or atopy, it has been proposed that a fall in common childhood infections may have been responsible for the rise in asthma. This study was undertaken to investigate the relationships between family size and reported allergic disease and to test the hypothesis that an inverse relationship between the two is a consequence of childhood infections.

METHODS

Data had been obtained in a 1964 cross sectional survey of a random sample of Aberdeen schoolchildren aged between 10 and 14 in that year. Records of the presence or absence of asthma, eczema, or hay fever at the time of the survey and a history of measles, pertussis, varicella, rubella, and mumps before and after the age of three years were available for 2111 subjects.

RESULTS

The risks of hay fever (odds ratio 0.2, 95% CI 0.1 to 0.8) and eczema (OR 0.3, CI 0.1 to 0.7) were inversely related to having had three or more older siblings, whilst the risk of asthma (OR 0.4, CI 0.1 to 0.9) was inversely related to having had three or more younger siblings. Increasing total numbers of siblings showed a significant trend in protection against both eczema and hay fever. A weak protective effect against asthma was found for measles after the age of three (OR 0.5, CI 0.3 to 0.9) and slight increases in the risk of eczema were associated with having had rubella or pertussis and of asthma with having had varicella. The number of infections before the age of three was associated with a significant trend in the odds ratios towards increased risk of asthma (p = 0.025). There were significant trends in the odds ratios towards greater risk of eczema and hay fever with increasing exposure to rubella, mumps, and varicella. These relations between infection and atopic diseases were independent of the potential confounding factors age, sex, father's social class, and total number of siblings.

CONCLUSIONS

These data add to the accumulating evidence that membership of a large sibship confers some protection against atopic disease. This does not appear to be explained by the common childhood infections which show conflicting relationships with atopic disease, in that measles may have some protective effect against asthma but the more infections a child has had, the more likely he or she is to have atopic disease. The explanation of the sibship effect is likely to lie elsewhere and the fall in common childhood infections is unlikely to explain the rise in atopic disease.

Genetics of host resistance and susceptibility to intramacrophage pathogens: a study of multicase families of tuberculosis, leprosy and leishmaniasis in north-eastern Brazil

Genetic analysis of disease phenotypes segregating in recombinant inbred, congenic and recombinant haplotype mouse strains permitted us to effectively "scan" the murine genome for genes controlling resistance and susceptibility to leishmanial infections. Five major regions were implicated which, because they show conserved synteny with regions of the human genome, immediately provide candidate gene regions for human disease susceptibility genes. A common intramacrophage niche for leishmanial and mycobacterial pathogens, and a similar spectrum of immune response and disease phenotypes, also led to the prediction that the same genes/candidate gene regions might be responsible for genetic susceptibility to mycobacterial infections such as leprosy and tuberculosis. Indeed, one of the murine genes (Nramp1) was identified for its role in controlling a range of intramacrophage pathogens, including leishmanial, salmonella and mycobacterial infections. In recent studies, multicase families of visceral leishmaniasis, tuberculosis and leprosy, from north-eastern Brazil have been analysed to determine the role of these candidate genes/regions in humans. Complex segregation analysis provides evidence for one or two major genes controlling susceptibility to these diseases in this population. Family-based linkage analyses (e.g., combined segregation and linkage analysis; sib-pair analyses) and transmission disequilibrium testing have been used to examine the role of four regions in disease susceptibility and/or immune response phenotypes. Results to date demonstrate: (1) the major histocompatibility complex (MHC:H-2 in mouse, HLA in humans: mouse chromosome 17/human 6p; candidates class II and class III including tumour necrosis factor alpha/beta genes) shows both linkage to, and allelic association with, leprosy per se, but is only weakly associated with visceral leishmaniasis and shows neither linkage to, nor allelic association with, tuberculosis; (2) no evidence for linkage between NRAMP1, the positionally cloned candidate for the murine macrophage resistance gene Ity/Lsh/Bcg (mouse chromosome 1/human 2q35), and susceptibility to tuberculosis or visceral leishmaniasis; (3) the region of human chromosome 17q (candidates NOS2A, SCYA2-5) homologous with distal mouse chromosome 11 is linked to tuberculosis susceptibility; and (4) the "T helper 2" cytokine gene cluster (proximal murine chromosome 11/human 5p; candidates IL4, IL5, IL9, IRF1, CD14) is not linked to human disease susceptibility for any of the three infections, but shows linkage to and highly significant allelic association with ability to mount an immune response to mycobacterial antigens. The demonstration of an allelic association between IL4 and immune response to mycobacterial antigen may provide a genetic explanation for the inverse association recently demonstrated between delayed hypersensitivity T helper 1 responses to mycobacterial antigen and atopic disorder in Japanese children. These studies demonstrate that the "mouse-to-human" strategy, refined by our knowledge of the human immune response to infection, can lead to the identification of important candidate gene regions in humans.