Is deficiency of interferon gamma production by allergen triggered cord blood cells a predictor of atopic eczema?

Reduced interferon gamma production by antigen-stimulated cord blood mononuclear cells is a risk factor of allergic disorders--6-year follow-up study

BACKGROUND

It is not sufficient to predict 'high allergic risk newborns' on the basis of increased IgE concentrations of cord blood alone, because a raised cord blood IgE concentration is specific but not sensitive in the prediction of the development of allergic disorders. Warner et al. have reported that interferon gamma (IFN-gamma) production by allergen-triggered cord blood cells is a predictor of atopic eczema, based on the 1-year follow-up study.

OBJECTIVE

We examined whether IFN-gamma production by antigen-stimulated cord blood mononuclear cells (CBMCs) is a risk factor of allergic disorders, based on the 6-year follow-up study.

METHODS

The relationships among cord blood IgE concentrations, IFN-gamma and interleukin-2 (IL-2) productions by antigen-stimulated CBMCs, and the development of allergic disorders in 21 infants for 6 years were investigated.

RESULTS

Atopic dermatitis, atopic dermatitis and allergic rhinitis, or atopic dermatitis and bronchial asthma developed in seven of 21 subjects. The maximal IFN-gamma concentration in culture supernatants of ovalbumin (OA) or bovine serum albumin (BSA) stimulated CBMCs in infants who developed allergic disorders was significantly lower (P < 0.01) than that in infants who did not develop any allergic disorders. In contrast, the maximal IL-2 concentration in culture supernatants of OA- or BSA-stimulated CBMCs in infants who developed allergic disorders was not lower than in infants who did not develop any allergic disorders. Moreover, the IFN-gamma concentrations were negatively correlated with cord blood IgE concentrations.

CONCLUSION

Reduced IFN-gamma production by antigen-stimulated CBMCs is a risk factor of allergic disorders.

Interferon-gamma pretreatment of peripheral blood mononuclear cells partially restores defective cytokine production in children with atopic dermatitis

Interferon-gamma (IFN-gamma) is considered an important determinant of the balance between T-helper type 1 and 2 cytokines and has been used experimentally for the treatment of atopic dermatitis. However, contrasting results have been reported relative to the Th-1/Th-2 cytokine profile in atopic patients. In this study, we examined cytokine production by polyclonally activated peripheral blood mononuclear cells (PBMC) from children with atopic dermatitis, and assessed the influence of in vitro IFN-gamma pretreatment on these cells. A fraction of PBMC isolated from children with severe atopic dermatitis, as well as from age-matched controls, was initially exposed to IFN-gamma. After washing, both treated and untreated cells were then put into culture either alone or with the addition of phytohemagglutinin (PHA) or phorbol myristate acetate (PMA) plus ionomycin. IL-4, IL-5, IL-10 and IFN-gamma production were measured in the supernatants using commercially available ELISAs. PBMC from atopic patients produced more IL-4 (P = 0.04) and IL-10 (P = 0.03) and less IFN-gamma (P = 0.01) than controls, when stimulated with PHA. Interestingly, in PMA + ionomycin stimulated cultures, the atopic cytokine profile was different with more IL-5 (P = 0.0068) and less IFN-gamma production (P = 0.00046) than the control group. When cells were pretreated with IFN-gamma, there were no significant differences between patients and controls. PBMC from children with atopic dermatitis show alterations in cytokine production, compatible in general terms with the Th-1/Th-2 model. Exposure of PBMC to IFN-gamma before activation results in a reduction of these differences, so that cytokine production becomes similar in the atopic and normal groups.

Programming for responsiveness to environmental antigens that trigger allergic respiratory disease in adulthood is initiated during the perinatal period

Allergy to airborne environmental antigens (allergens) is a major cause of asthma in children and adults. This review argues that the development of allergen-specific immunologic memory of the type that predisposes to allergy development is the end result of a T-cell selection process operative during infancy, which is triggered via encounters between the immature immune system and incoming airborne allergens from the environment. In normal individuals this process leads to the development of allergen-specific T-memory cells that secure the T helper (Th)-1 pattern of cytokines, which actively suppress the growth of their allergy-inducing Th-2 cytokine-secreting counterparts. However, these protective allergen-reactive Th-1 memory cells fail to develop in some individuals, permitting the subsequent proliferation of allergen-specific Th-2 cells that can trigger allergic reactions. Recent evidence suggests that genetic predisposition to allergy may be due in part to hyperactivity of control mechanisms operative in utero and which normally protect the fetoplacental unit against the toxic effect of Th-1 cytokines.

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.

Enhanced IL-4 but normal interferon-gamma production in children with isolated IgE mediated food hypersensitivity

Atopic disorders such as atopic dermatitis and asthma have been characterised by an imbalance in interferon-gamma (INF-gamma) and IL-4. Whether similar imbalances are found in atopic disorders with different clinical manifestations, such as IgE mediated immediate food hypersensitivity, is not clear. We have examined the in vitro production of INF-gamma and IL-4 in peripheral blood mononuclear cells (PBMC) following phytohaemagglutinin stimulation from children with isolated immediate IgE mediated food hypersensitivity (egg, milk, "nut"), children with moderate and severe atopic dermatitis, and normal children. Children with immediate food reactions were excluded if they had a history or evidence of atopic dermatitis or asthma. PBMC from children with IgE mediated food hypersensitivity produced significantly more IL-4 (p = 0.013) but equivalent INF-gamma (p = 0.26) compared to PBMC from control children. In contrast, PBMC from children with atopic dermatitis produced significantly less INF-gamma (p < 0.001) and more IL-4 (p < 0.008) than PBMC from normal children. In addition, there was no difference in IL-4 (p = 0.74) but significantly less INF-gamma (p < 0.001) produced by PBMC from the children with atopic dermatitis than food hypersensitivity. We demonstrate that children with IgE mediated food hypersensitivity and no other manifestation of atopic disease have enhanced IL-4 production without the defect in INF-gamma production observed in childhood AD and asthma. We postulate that isolated IL-4 enhancement promotes the development of IgE mediated hypersensitivity disorders such as food allergy, whilst the combination of defective INF-gamma and enhanced IL-4 production promotes inflammatory atopic disorders such as AD and asthma.

Electrostatic charge characteristics of Der p1 allergen-carrying particles and the house dust mite dermatophagoides pteronyssinus

Control of the house dust mite allergen has received considerable attention owing to its importance in some allergic diseases. One aspect of dust mites and their allergen-carrying faecal particles that has not been reported on, which may have allergen control applications, is the electrostatic charge they carry in the natural environment. To promote tribo-electric charging, household dust containing dust mite allergen and live house dust mites are separately agitated while in contact with either polypropylene, nylon or earthed metal. The charged dust and mites are subsequently subjected to electrostatic separation and collection. Results for concentrations of the house dust mite allergen, Der p1, indicate that, when subjected to nylon, Der p1 carrier particles appear to be predominantly positively charged. Similarly, when subjected to polypropylene, Der p1 carrier particles also appear to be positively charged. Reduction of excess free charge by agitation against earthed metal does not appear to affect the observed charging characteristics, indicating that the positive charge may be bound or inherent in the Der p1 carrier particles. In contrast, house dust mites exposed to nylon appear to be generally charging negative, whereas mites exposed to polypropylene appear to be charging positive. The observed electrostatic characteristics of the mites and Der p1 carrying particles will be useful in the future development of electrostatic allergen control methods.

Peanut allergic subjects' peripheral blood mononuclear cell proliferative responses to crude peanut protein

BACKGROUND

Peanut allergy is characterized by a high frequency of severe and occasionally fatal reactions.

OBJECTIVE

To determine if there are features of the in vitro cellular response that may account for the observed severity of peanut allergy.

METHODS

Skin-prick testing (SPT), RAST assay of serum peanut-specific and total IgE and mixed peripheral blood mononuclear cells (PBMC) proliferative responses to crude peanut protein were measured in 44 peanut allergics with varying severity of clinical reactions. PBMC responses of 13 non-peanut allergic controls (six atopic) were also studied.

RESULTS

Subjects' PBMCs proliferated more than controls', even without stimulation. Subjects' PBMC proliferative responses did not correlate with clinical severity, SPT weal size or peanut-specific IgE levels. Controls' PBMCs did not respond to peanut. There was no correlation between PBMC response and time since last reaction to peanut. Subjects' PBMCs responded more than controls, to mitogen as well as allergen. Proliferation increased with increasing concentration of peanut protein (P < 0.0001).

CONCLUSION

PBMCs of peanut allergics demonstrate a dose-dependent response to peanut which does not correlate with clinical severity, SPT reaction or levels of peanut specific IgE. The response is antigen-specific. Peanut protein is not mitogenic and is not acting as a superantigen. While there are non-specific differences in the PBMC responses of peanut allergic individuals compared with atopic and non-atopic controls, these differences do not explain the unique severity of peanut allergy.

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.

CD8+ T cells control Th2-driven pathology during pulmonary respiratory syncytial virus infection

BALB/c mice vaccinated with vaccinia virus expressing the major surface glycoprotein G of respiratory syncytial virus (RSV) develop lung eosinophilia during RSV challenge. The G protein is remarkable in that it induces CD4+, but no CD8+ T cells in this mouse strain. Studies using passive T cell transfers show that co-injection of CD8+ T cells greatly reduces the Th2-driven lung eosinophilia caused by G-specific CD4+ T cells. By contrast, vaccination with the fusion protein (F) induces both CD8+ and CD4+ T cells, but not lung eosinophilia during RSV infection. These observations suggest that CD8+ T cells play a crucial role in preventing Th2-driven pathology. We therefore depleted mice with anti-CD8 antibodies in vivo. This treatment allowed lung eosinophilia to develop in F-primed mice. Depletion of interferon (IFN)-gamma had a similar effect, suggesting that secretion of this cytokine is the mechanism by which CD8+ T cells exert their effect. To test whether similar effects occurred in other strains of mice, RSV-infected C57BL/6 mice (which do not develop eosinophilia after sensitization to G) were treated with anti-IFN-gamma. Again, these mice developed eosinophilia. In this strain, genetic deletion of CD8-alpha, beta2-microglobulin or genes coding for the transporter associated with antigen presentation (which in each case eliminates CD8+ T cells) caused lung eosinophilia during RSV infection. These studies show the critical roles that CD8+ T cells and IFN-gamma production play in regulating Th2-driven eosinophilia and provide a unifying explanation for previous studies of lung eosinophilia. We propose that vaccines designed to enhance CD8+ T cell recognition might avoid disease caused by CD4+ Th2 cells.

The allergy march: from food to pollen

There is epidemiological evidence, especially from longitudinal studies, that clinical manifestations of atopy as well as IgE antibodies against food and aeroallergens show a systematic sequence of events. The atopic march begins with food allergy associated gastrointestinal disorders and atopic dermatitis followed by respiratory allergies, i.e. asthma and atopic rhino-conjunctivitis. Detectable food antibodies, especially against egg and milk proteins, usually precede or accompany the early clinical symptoms and signs. Similarly, aeroallergen sensitization, first against indoor allergen antibodies, succeeded by outdoor allergen antibodies, precede the clinical manifestation of respiratory allergy. Early atopic events, either manifestation or sensitization can be used as risk markers or even predictors of atopic disorders to implement preventive measures. Early atopic dermatitis as well as elevated serum IgE antibodies against food allergens in the first two years of life in combination with a family history can be used as a predictor for aeroallergen sensitization.

The frequency of cells secreting interferon-gamma and interleukin-4, -5, and -10 in the blood and duodenal mucosa of children with cow's milk hypersensitivity

Enzyme-linked immunoabsorbant spots (ELISPOTs) have been used to analyze the frequency of cells spontaneously secreting interferon-gamma (INF-gamma), IL-4, IL-5, or IL-10 in mononuclear cells isolated from the blood of children with cow's milk-sensitive enteropathy (CMSE), cow's milk allergy (CMA), and age-matched controls. In addition, cytokine profiles of duodenal lamina propria lymphocytes were compared in patients with CMSE and control subjects. In blood, spontaneous cytokine-secreting cells were uncommon, but there was significantly increased IFN-gamma, IL-4, IL-5, and IL-10 ELISPOTs in children with CMSE and CMA compared with control subjects. IL-4 ELISPOTs were significantly greater in the blood of children with CMA compared with those with CMSE. In the lamina propria the frequencies of spontaneous cytokine-secreting cells were high compared with that in blood. Significantly increased ELISPOTs for IFN-gamma and IL-4 were found in CMSE compared with controls. IL-5 ELISPOTs were unchanged, and IL-10 ELISPOTs were reduced in CMSE compared with controls. These results show a general enhancement of Th1 and Th2-type cytokine-secreting cells in the blood of children with cow's milk hypersensitivity, although the increased IL-4-secreting cells in blood in CMA may be of relevance in view of the fact that this disease is IgE-mediated. In the lamina propria, there is also enhancement of IFN-gamma- and IL-4-secreting cells in CMSE compared with control subjects; however, cells secreting IFN-gamma are 10 times more numerous than cells secreting IL-4, showing a dominance of Th1-type responses in both controls and CMSE patients.

Factors predicting food allergy

Prediction of food allergies has not been addressed systematically and to date studies have concentrated on prediction of allergic disorders in a general fashion. The current available data suggests that possibly the best predictor is the combined approach of taking into account the family history together with elevated cord blood IgE. Other indicators, such as cord blood lymphocyte responses and γ-interferon production at birth, are also discussed. Although preliminary studies seem to be promising, only studies of an unselected population with long term follow-ups will be able to show whether or not these possible predictors are of value.

Cytokines in nasal fluids from school children with seasonal allergic rhinitis

Allergic rhinitis is a particularly good model for studies of cytokine production in vivo. In this study the occurrence of the cytokines IL-4, IL-5, IL-10 and IFN-gamma as well as the soluble receptor for IL-4 in nasal lavage fluids were assayed in 38 school children, with seasonal allergic rhinitis, and 19 healthy age-matched, non-atopic controls, using highly sensitive enzyme immunoassays. IL-4 levels in patients with seasonal allergic rhinitis were markedly increased in comparison with those in non-atopic controls or in atopic patients before the start of the pollen season. In controls, but not in the atopic patients, levels of IFN-gamma and IL-5 were significantly higher in specimens obtained during the pollen season than in those obtained outside the season. The IL-4/IFN-gamma ratios were significantly higher in atopic than in non-atopic subjects and further increased in atopic patients during the season. In addition to IL-4, elevated levels of IL-10 were observed in association with seasonal rhinitis. Following treatment with a topical steroid (budesonide) there was a statistically significant increase of the levels of soluble IL-4 receptor. These findings indicate that nonatopic and atopic individuals react to pollen exposure with distinct cytokine patterns in agreement with the Th1/Th2 concept. Topical steroids may possibly decrease inflammation by increasing the formation of soluble IL-4 receptor.

Neonates at risk of atopy show impaired production of interferon-gamma after stimulation with bacterial products (LPS and SEE)

Recent studies demonstrate reduced interferon-gamma (IFN-gamma) secretion in neonates who became atopic later in life. The underlying pathomechanism is still unknown. We therefore examined the effects of bacterial products on neonatal IFN-gamma production acting through different T-cell- or antigen-presenting-cell (APC)-stimulating mechanisms: cord-blood mononuclear cells (CBMC) were incubated with lipopolysaccharide (LPS), staphylococcal enterotoxin E (SEE), or a combination of both and restimulated with PMA and ionomycin. LPS and SEE as single stimuli induced IFN-gamma production to the same extent in CBMC of neonates with high and low risk of atopy. In contrast, a combination of LPS and SEE had a multiplying effect on IFN-gamma secretion only in CBMC of neonates with low risk of atopy. Phenotype analysis revealed that only memory T cells showed impaired IFN-gamma synthesis (median 3.6% IFN-gamma-producing cells vs 14.2% in controls: P < 0.01), whereas IFN-gamma production by naive T cells did not differ in either group. Taken together, these results point to the existence of a disturbed function of costimulatory mechanisms in neonates at high risk of atopy, provoking reduced memory T-cell IFN-gamma production.

Atopic versus infectious diseases in childhood: a question of balance?

There is an increasing interest in the concept that respiratory tract infections during early childhood may in some circumstances confer protection against sensitisation to aeroallergens, via "bystander" stimulation of Th-1 associated immune functions in the regional lymph nodes draining the airway mucosa. We hypothesise below that this phenomenon may be but one component of a broader process operative during early postnatal life, in which generalised contact with the microbial environment plays an obligatory role in stimulating the functional maturation of the Th-1 arm of the immune response. We argue further that one of the most potent sources of such stimulation is provided by the normal commensal flora of the gastrointestinal tract, which is establish during early infancy.

Evaluation of the usefulness of lymphocyte proliferation assays in the diagnosis of allergy to cow's milk

BACKGROUND

The significance of cell-mediated mechanisms in IgE-mediated milk allergy (IgE-MA) and in milk-induced enterocolitis syndrome (ME) is controversial. Some investigators have claimed that lymphocyte proliferation assays are useful in the diagnosis of food hypersensitivity, despite the great variability in study designs and results reported. This study was undertaken to address many of these variables and to determine whether lymphocyte proliferation assays correlate with clinical diagnoses.

METHODS

Lymphocyte proliferative responses to milk antigen were evaluated in two groups of children, 27 with IgE-MA, and nine with ME and in 21 pediatric control subjects. IgE-mediated food allergy was documented by positive double-blind, placebo-controlled food challenges and positive skin prick test results. ME was diagnosed by oral challenge or by a history of repeated episodes of delayed vomiting (>2 hours) after ingestion of milk and by negative skin prick test responses. Peripheral blood mononuclear cells were isolated and cultured. Cultures stimulated with milk (the food antigen of interest), soy antigen (a nonrelevant food antigen), or tetanus antigen (a positive control antigen) and unstimulated controls were performed in quadruplicate. On days 5, 7, and 9, cells were pulsed with tritium-labeled thymidine and incubated for 4 hours. Results were compared as counts per minute (cpm) and as stimulation indices (SIs).

RESULTS

Maximal proliferation was generally seen on day 7. The median cpm (20,941) and the median SI (19.2) in response to milk antigen in the 27 children with IgE-MA were significantly greater than those in the control patients (6969 cpm; SI = 14.2; p = 0.001 and p < 0.05, respectively). However, the ranges were large and overlapped extensively (IgE-MA, 5616 to 52,053 cpm; controls, 469 to 39,260 cpm). The non-soy-allergic patients with IgE-MA also had a significantly greater response to soy antigen than did the control subjects when cpm were compared (0.01 < p < 0.05). There were no differences in background or in response to tetanus antigen. The median response to milk in the patients with ME (11,975 cpm) was significantly greater than that in control subjects (6969 cpm; 0.01 < p < 0.05), when cpm were compared but not when SIs were compared. There were no significant differences between the patients with IgE-MA and those with ME.

CONCLUSION

Overall, these results indicate that lymphocyte proliferation assays are neither diagnostic nor predictive of clinical reactivity in individual patients with milk allergy. Lymphocytes of many control patients are highly responsive to milk antigens, and lymphocytes of many patients with milk allergy are not. Statistically significant differences are only evident when the patients are compared as groups.

Early intervention for the prevention of atopic dermatitis

Based on a lecture given to the European Society for Pediatric Allergy and Clinical Immunology. Diseases associated with atopy are increasing throughout the world. Individuals appear to have a genetic predisposition to atopy which is then provoked by environmental influences. Ingested or inhaled allergens provoke an antibody response and a state of sensitization. In many but not all sensitized individuals subsequent exposure to allergen will provoke a release of histamine and other mediators from sensitized mast cells and produce clinical signs of an allergic reaction in the target organ or throughout the body. At the present time one approach to the prevention or reduction of such reactions appears to be the identification of the high-risk infant and then preventing or limiting exposure to the potentially allergenic protein materials in the child's diet or immediate environment. This paper outlines the problems of identifying high-risk infants and comments on the success claimed in the intervention studies that have been undertaken. The possible hazards to mothers and infants of dietary exclusion are emphasized and the provision of appropriate medical and dietetic support are regarded as of paramount importance. Although more studies are needed, the Isle of Wight intervention programme offers hope to families at high-risk of atopy that the problem can be reduced for the next generation.

Allergen recognition in the origin of asthma

Allergic respiratory diseases such as bronchial asthma are believed to result directly from the repeated local expression in airway tissues of T helper (Th) 2-polarized T cell immunity to inhaled allergens. Recent evidence suggests that these T cell responses are typically primed in utero and subsequently reshaped during postnatal allergen exposure via immune deviation, leading to the eventual emergence of stable allergen-specific T cell memory which is polarized towards the Th1 (normal) or Th2 (atopic) phenotype. The underlying Th1/Th2 switching process is influenced by a number of host and environmental factors that are poorly understood. Prominent amongst these are factors that affect the kinetics of maturation of immune competence during the early postnatal period. In particular, there is mounting evidence that the immunological milieu at the materno-fetal interface is naturally skewed towards the Th2 phenotype (possibly an evolutionary adaptation to protect the placenta against the toxic effects of Th1 cytokines). Furthermore, this bias appears to be preserved for varying periods into infancy, which may account for the presence of a high risk 'window' for allergic sensitization in early postnatal life. It is hypothesized that the principal impetus for postnatal development of a normal Th1/Th2 balance (and hence closure of the high risk sensitization window) is provided via contact with Th1-stimulatory commensal and pathogenic micro-organisms at the body's major mucosal surfaces.

Prenatal origins of asthma and allergy

The prevalence of asthma and related allergic disorders has increased considerably over the last 25 years. Genetic stock has not changed, so environmental factors must have influenced the phenotype. Infants who develop allergy already have an altered immune response at birth. We have investigated the development of immune responses during gestation and the effect of maternal allergen exposure during pregnancy and infant exposure in the first month of life on the development of allergy and disease. There was higher specific peripheral blood mononuclear cell proliferation to house dust mite (P = 0.01) and birch pollen (P = 0.004) in the third trimester compared with the second trimester, with the first positive responses seen at 22 weeks gestation. Maternal exposure to birch pollen after 22 weeks resulted in higher (P = 0.005) infant peripheral blood mononuclear cell responses to birch pollen at birth. Infants born at term, with at least one atopic, asthmatic parent, who developed allergic symptoms and positive skin prick test by one year of age had raised proliferative responses to house dust mites at birth compared to those with no symptoms (P = 0.01). In genetically predisposed individuals, antenatal factors, including maternal and thereby fetal exposure to allergens and maternoplacental-fetal immunological interactions, are active in determining whether an allergic predisposition is manifested as disease.

Asthma: a dynamic disease of inflammation and repair

It is now widely accepted that asthma in its varied forms is an inflammatory disorder of the airways in which mediator release from activated mast cells and eosinophils plays a major role. T lymphocytes take a primary role in orchestrating these processes through their capacity to generate a range of cytokines of the interleukin 4 gene cluster encoded on the long arm of chromosome 5. Additional cytokines derived from mast cells and eosinophils also play a key role, especially tumour necrosis factor alpha, which is responsible for initiating the up-regulation of vascular adhesion molecules involved in the recruitment of eosinophils and other inflammatory cells from the circulation. The importance of C-X-C and C-C chemokines as local chemoattractants and activating stimuli is also recognized. In addition to releasing an array of pharmacologically active autacoids, the inflammatory response in asthma results in the generation of proteolytic activities from mast cells (tryptase, chymase), eosinophils (MMP-9) and the epithelium itself (MMP-2, MMP-9), which exert tissue-destructive and cell-signalling effects. The epithelium is also highly activated, as evidenced by the up-regulation of cytokine production, inducible enzymes and soluble mediators. Increased surface expression of the epithelial isoform of CD44 (9v) and subepithelial proliferation of myofibroblasts are indicative of a simultaneous active repair process and the laying down of new interstitial collagens. Together, inflammatory and repair processes create the complex phenotype that characterizes asthma and its progression.

Abnormal production of T helper 2 cytokines interleukin-4 and interleukin-5 by T cells from newborns with atopic parents

T cell clones were generated from umbelical cord blood lymphocytes (UCBL) of nine newborns with atopic or nonatopic parents and their cytokine secretion profile was assessed. Both phytohemagglutinin-induced and Dermatophagoides pteronyssinus-specific T cell clones from newborns with atopic parents exhibited an enhanced ability to produce the Th2 cytokines interleukin (IL)-4 and IL-5, compared to T cell clones from newborns with nonatopic parents. In contrast, the ability to produce interferon-gamma by UCBL from the two groups of newborns was not different. Of the five children who could be followed up to 3 years after birth, four with atopic parents developed clinical and/or biological atopic manifestations, whereas one without atopic parents did not. Thus, the pronounced production of IL-4 and IL-5 by UCBL not only appears to be related to the atopic status of parents, but also associates with the subsequent development of atopy in childhood.

Development of immune functions related to allergic mechanisms in young children

The newborn immune system differs quantitatively and functionally from that of adults. Development of the immune system has important implications for childhood diseases. The immaturity of the immune system in the first years of life may contribute to failure of tolerance induction and in the development of allergic disease. T cell function is diminished, especially the capacity to produce cytokines; production of interferon (IFN)-gamma, and IL-4 is strongly reduced. IFN-gamma has been found to be even lower in cord blood of newborns with a family history of atopy. Differences in other cell types (natural killer cells, antigen-presenting cells, and B cells) could also play a role in the development of allergic disease. Current data suggest that irregularities in IgE synthesis, helper T cell subsets (Th1, Th2, CD45RA, and CD45RO), cytokines (IL-4, IFN-gamma), and possibly other cell types may play a role in the development of allergy in childhood. Moreover, the role of cell surface molecules, like co-stimulatory molecules (CD28, CD40L), activation markers (CD25), and adhesion molecules (LFA-1/ICAM-1, VLA-4/ VCAM-1) is also discussed. These variables are modulated by genetic (relevant loci are identified on chromosome 5q, 11q, and 14) and environmental forces (allergen exposure, viral infections, and smoke). The low sensitivity of current predictive factors for the development of allergic diseases, such as cord blood IgE levels, improves in combination with family history and by measurement of in vitro responses of lymphocytes and skin reactivity to allergens. New therapeutic approaches are being considered on the basis of our current understanding of the immunopathology of allergic disease, for instance cytokine therapy and vaccination with tolerizing doses of allergen or peptides.

Fetal peripheral blood mononuclear cell proliferative responses to mitogenic and allergenic stimuli during gestation

Blood samples were obtained from fetuses and premature babies (n = 51) (15-34 weeks gestation) to determine at what stage the fetal immune system was able to produce a positive proliferative response to common allergens. Peripheral blood mononuclear cells (PBMC) were stimulated with the mitogen, phytohaemagglutinin (PHA), and the allergens, house dust mite, cat fur, birch tree pollen, beta-lactoglobulin, ovalbumin and bee venom (mellitin). Results were expressed as ratios of stimulated to unstimulated 3H thymidine incorporation, and as percent positive responders. There was an increase in proliferation ratio which correlated with increasing gestational age for PHA (p < 0.0001), cat fur (p = 0.042), birch pollen (p = 0.022) and beta-lactoglobulin (p = 0.006). The point in gestation when cells from some individuals began responding to the allergens with a ratio of 2.0 was at approximately 22 weeks. PBMC proliferative response ratios were higher from samples from babies > 22 weeks gestation compared to < 22 weeks for the mitogen and all allergens, except mellitin. There was also a greater proportion of positive responders from samples > 22 weeks compared to < 22 weeks for the mitogen and all allergens, except mellitin. Maternal exposure to birch pollen, which has a discrete season, was assessed to determine whether exposure had occurred at 22 weeks gestation or beyond. Results showed a higher proliferative response in infant cells stimulated with birch pollen (p = 0.005) and higher proportion of positive responders (p = 0.01) in the group of babies whose mothers had been exposed to birch pollen beyond 22 weeks, compared to those whose mothers had not been so exposed. These results suggest that in utero fetal exposure to an allergen from around 22 weeks gestation may result in primary sensitisation to that allergen, leading to positive proliferative responses, at birth.

Atopic dermatitis: an update

This review focuses on recent literature regarding the following clinical features of atopic dermatitis (AD); diagnostic criteria, epidemiology and genetics, provocative factors, predictors of disease development and markers of disease severity, therapy, and prognosis. For example, the frequency of AD appears to be increasing, perhaps in response to provocative factors such as food allergens and house dust mites. Determination of reliable markers for disease development may identify susceptible newborns and facilitate avoidance of relevant triggers. Immunomodulating therapy holds promise in the treatment of refractory AD, and new investigation has led to refinements in conventional modalities such as antihistamines and phototherapy.

Candidate gene loci in asthmatic and allergic inflammation

New techniques for scanning the human genome promise great advances in tracking the origins of disorders caused by multiple genes. However, it is clear from the studies presented in this overview that we are far from understanding the genetic basis of asthma and atopy and their interaction with the environment. It is also clear that agreement must be reached on definition of the phenotype and methods of ascertainment in order to carry out large multicentre collaborative studies. Positive findings need to be validated in different populations selected for the presence of the disease and then confirmed in a random population where the prevalence of asthma and atopy will also be expected to be significant.

Environmental antigens and atopic disease: underlying mechanisms and prospects for therapy and prophylaxis

Natural exposure to non-pathogenic antigens, the so-called 'environmental antigens', experimentally elicits a characteristic pattern of T-cell immunity, involving selective suppression of the T-cell-dependent IgE responses that trigger allergic reactions. This 'immune deviation' results in the generation of long-lived T-cell memory, which confers active protection against allergic sensitization. Corresponding primary immune responses to environmental antigens in humans occur most frequently during infancy, and the development of allergic sensitization can be viewed as a failure of this natural immune-deviation process. In this article, potential strategies for primary prevention of allergic disease in infants involving, in particular, the exploitation of oral and mucosal tolerance to stimulate protective CD8+ T-cell-mediated immune deviation, are discussed.