The heterogeneity of allergic phenotypes: genetic and environmental interactions

OBJECTIVE

This article reinforces the reader's knowledge of the multifactorial nature of allergic diseases and of the heterogeneity of allergic phenotypes.

DATA SOURCES

Personal studies and an evidence-based approach is used to support the assumption that three major abnormalities concur in the pathophysiology of allergic diseases: 1) enhanced allergen recognition and specific immune response; 2) a T helper 2 cytokine profile that results in polyclonal immunoglobulin E activation and mast cell-eosinophilic inflammation; and 3) organ hyperreactivity.

STUDY SELECTION

Examples of genetic and environmental factors that preferentially influence each of these distinct pathophysiologic abnormalities are provided.

RESULTS

Data presented indicate that allergic diseases distribute along a wide spectrum depending on the preferential pathophysiologic abnormalities operating in the individual patient.

CONCLUSIONS

Categorization of allergic patients into distinct clinical phenotypes might result in a more patient-oriented (rather than disease-oriented) approach, and hence, better management.

Prevalence of atopy and asthma in eastern versus western Europe: why the difference?

LEARNING OBJECTIVES

This article reinforces the reader's knowledge of the epidemiology of allergy and asthma in eastern versus western European countries and the ability to recognize the different hypotheses formulated to explain the rising trend of allergic asthma in Europe.

DATA SOURCES

Articles in English comparing the epidemiology of allergy in eastern versus western Europe published before December 31, 2000.

RESULTS

Significant higher prevalences of atopy and allergic asthma were observed in the early 1990s among populations living in western compared with eastern European countries. Changes in lifestyle after the fall of the communist system were associated with an increasing trend of atopic sensitization and hay fever in former East Germany after only 6 to 8 years after the Germany reunification. It has been hypothesized that a similar "converging" trend in the prevalence of allergic asthma and of bronchial hyperresponsiveness may take longer periods.

CONCLUSIONS

The prevalence of allergic asthma has increased decades earlier in western Europe with respect to eastern Europe. This is probably attributable to changes in lifestyle that had already occurred rather than to air pollution. The factors of a western lifestyle (diet, hygiene, varied allergen exposure) that have determined the difference in allergic asthma prevalence across Europe have yet to be identified.

Are infections protecting from atopy?

The 'Hygiene Hypothesis' proposes that overcrowding and unhygienic contacts early in life may protect from atopic diseases by facilitating exposure to microbes. Longitudinal studies have recently shown that among subjects exposed early in life to other children at home, or at day care, the risk of wheezing steadily declined with age to levels significantly lower than controls. Evidences supporting a protective role of respiratory infections or BCG immunization on the development of allergic asthma are still insufficient. By contrast, the observation of a lower prevalence of atopic sensitization among children raised on a farm has been consistently reproduced. Several new studies have recently investigated the role of changes of human microbial flora, declining exposure to foodborne and orofecal infections, to helminths and to environmental sources of endotoxin as putative contributors to the rise of allergy and asthma cases among populations living with a western lifestyle.

Exposure to foodborne and orofecal microbes versus airborne viruses in relation to atopy and allergic asthma: epidemiological study

OBJECTIVE

To investigate if markers of exposure to foodborne and orofecal microbes versus airborne viruses are associated with atopy and respiratory allergies.

DESIGN

Retrospective case-control study.

PARTICIPANTS

240 atopic cases and 240 non-atopic controls from a population sample of 1659 participants, all Italian male cadets aged 17-24.

SETTING

Air force school in Caserta, Italy.

MAIN OUTCOME MEASURES

Serology for Toxoplasma gondii, Helicobacter pylori, hepatitis A virus, measles, mumps, rubella, chickenpox, cytomegalovirus, and herpes simplex virus type 1; skin sensitisation and IgE antibodies to relevant airborne allergens; total IgE concentration; and diagnosis of allergic asthma or rhinitis.

RESULTS

Compared with controls there was a lower prevalence of T gondii (26% v 18%, P=0.027), hepatitis A virus (30% v 16%, P=0.004), and H pylori (18% v 15%, P=0.325) in atopic participants. Adjusted odds ratios of atopy decreased with a gradient of exposure to H pylori, T gondii, and hepatitis A virus (none, odds ratio 1; one, 0. 70; two or three, 0.37; P for trend=0.000045) but not with cumulative exposure to the other viruses. Conversely, total IgE concentration was not independently associated with any infection. Allergic asthma was rare (1/245, 0.4%) and allergic rhinitis infrequent (16/245, 7%) among the participants (245/1659) exposed to at least two orofecal and foodborne infections (H pylori, T gondii, hepatitis A virus).

CONCLUSION

Respiratory allergy is less frequent in people heavily exposed to orofecal and foodborne microbes. Hygiene and a westernised, semisterile diet may facilitate atopy by influencing the overall pattern of commensals and pathogens that stimulate the gut associated lymphoid tissue thus contributing to the epidemic of allergic asthma and rhinitis in developed countries.

Mimicking microbial 'education' of the immune system: a strategy to revert the epidemic trend of atopy and allergic asthma?

Deficient microbial stimulation of the immune system, caused by hygiene, may underly the atopy and allergic asthma epidemic we are currently experiencing. Consistent with this 'hygiene hypothesis', research on immunotherapy of allergic diseases also centres on bacteria-derived molecules (eg DNA immunostimulatory sequences) as adjuvants for allergen-specific type 1 immune responses. If we understood how certain microbes physiologically 'educate' our immune system to interact safely with environmental nonmicrobial antigens, we might be able to learn to mimic their beneficial actions. Programmed 'immunoeducation' would consist of safe administration, by the correct route, dose and timing, of those microbial stimuli that are necessary to 'train' the developing mucosal immune system and to maintain an appropriate homeostatic equilibrium between its components. Overall, this would result in a prevention of atopy that is not limited to certain specific allergens. Although such a strategy is far beyond our present potential, it may in principle revert the epidemic trend of atopy and allergic asthma without jeopardizing the fight against infectious diseases.

Incidence of Helicobacter pylori infection in a cohort of Italian military students

Prevalence and incidence of Helicobacter pylori infection among 250 Italian military students were studied using specific IgG antibodies. Subjects susceptible at enrollment were evaluated during a 10-month follow-up period, when two serum samples were collected after 5 and 10 months, respectively. Samples were also analyzed for anti-CagA (a protein associated with virulent H. pylori strains) IgG antibodies. Finally, spectrotypic analysis by isoelectric focusing and reverse blotting (IEFRB) was performed in the majority of positive samples. Forty-three out of 250 (17.2%) were positive at the time of enrollment, a seroprevalence rate very similar to that observed in a larger Italian military population 5 years earlier. Among the 207 susceptible subjects, two seroconverted at 5 months after enrollment; they were still positive at the end of follow-up (incidence rate of 1.16 per 100 person/years of exposure). This data suggests a spread of H. pylori in the Italian military population that is not negligible. Nearly all anti-H. pylori-positive subjects were also CagA antibody positive (agreement percentage: 97.6%; K = 0.91), suggesting that the large majority of H. pylori strains were of the virulent type. Sixty-four percent of positive sera presented an oligoclonal spectrotype, which seems to be a hallmark of humoral immune response to H. pylori.

Association of persistent bronchial hyperresponsiveness with beta2-adrenoceptor (ADRB2) haplotypes. A population study

Bronchial hyperresponsiveness (BHR) is a hallmark of asthma and represents a strong risk factor for the disease. However, not all asthmatics have BHR and it can be observed in normal subjects too, probably because of genetic predisposition. Increasing attention is being focused on the beta2-adrenoceptor gene (ADRB2), whose genetic variability at amino acids 16 and 27 has been shown to correlate with some clinical features of asthma, including airways reactivity. To verify whether ADRB2 gene polymorphisms can influence BHR at a broader level, we studied a large, highly homogeneous sample of individuals sharing race, gender, age, and current living environment. BHR was strictly defined as a constant positive response to serial methacholine challenge tests and an improved definition of genetic variability at the ADRB2 locus was used, by identifying the haplotypic combinations of polymorphisms 16 and 27. We observed that the ADRB2 haplotype with a Gly at position 16 and a Gln at position 27 is associated with BHR in our sample. The association persisted also after correction for potentially confounding variables such as specific and total IgE levels. This observation suggests therefore that ADRB2 gene can confer genetic susceptibility to BHR, rather than having only a disease-modifying effect in asthma.

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.

Prevalence of Helicobacter pylori infection in a cohort of Italian military students

In 1990, to study regional prevalences and risk factors of Helicobacter pylori infection in healthy young adult males, sera were collected from a nationwide sample of 1659 males (mean age 20.7 years) at introduction into the Air Force School for military students in Caserta, Italy. An enzyme-linked immunosorbent assay was used to detect H. pylori specific immunoglobulin G antibodies. The observed overall seropositivity rate was 17.5% (95% CI 15.7-19.4). Prevalence was higher in southern Italy and in the Italian islands as compared with northern Italy and central Italy (21.3% vs. 9.5%). Multiple logistic regression analysis showed that residence in southern areas and islands was the strongest predictor of the likelihood of H. pylori seropositivity; number of siblings in the household was marginally associated; years of father's schooling was not a significant predictor. H. pylori positive subjects were more likely positive for antibodies to hepatitis A virus infection (anti-HAV) than those H. pylori negative (35.4% vs. 24.9%; Odds Ratio 1.7, 95% CI 1.3-2.2). Adjustment for the confounding effect of sociodemographic variables weakened this association (OR 1.3, 95% CI 1.0-1.7). These findings suggest that differences in environmental conditions rather than in socioeconomic status may have played the major role in the different spread of H. pylori infection across the country.

Cross sectional retrospective study of prevalence of atopy among Italian military students with antibodies against hepatitis A virus

OBJECTIVE

To investigate the working hypothesis that common infections occurring early in life prevent atopy.

DESIGN

Cross sectional, retrospective study of young Italian men with results for hepatitis A serology and atopy.

SETTING

Air force school of military students in Caserta, Italy.

SUBJECTS

1659 male students aged 17-24, most of whom (90%) were from central and southern Italy.

MAIN OUTCOME MEASURES

Skin sensitisation and specific IgE antibodies to locally relevant airborne allergens; diagnosis of respiratory allergy (asthma or rhinitis, or both); hepatitis A seropositivity.

RESULTS

443 of the 1659 subjects (26.7%) were positive for hepatitis A virus antibody. Atopy was less common among seropositive than seronegative subjects according to skin sensitization (weal reaction > or = 3 mm) to one or more allergens (21.9% (97/443) v 30.2% (367/1216), P < 0.001); polysensitisation (sensitive to three or more allergens) (2.7% (12/443) v 6.4% (78/1216), P < 0.01); high specific IgF concentration (9.7% (43/443) v 18.4% (224/1216), P < 0.00005); and lifetime prevalence of allergic rhinitis or asthma, or both (8.4% (37/443) v 16.7% (203/1216), P < 0.001). Hepatitis A seropositivity remained inversely associated with atopy after adjusting for father's education, the number of older siblings, and the area of residence (based on the number of inhabitants). The prevalence of atopy was constantly low among seropositive subjects, whatever the number of older siblings; by contrast, it increased with a decreasing number of older siblings among seronegative subjects.

CONCLUSION

Indirect but important evidence is added to the working hypothesis as common infections acquired early in life because of the presence of many older siblings (among seronegative subjects) or because of unhygienic living conditions (among seropositive subjects) may have reduced the risk of developing atopy.

Lack of evidence for a superantigen in lymphocytes from HIV-discordant monozygotic twins

OBJECTIVE

An HIV-associated superantigen (SAg) has been hypothesized. Here we test whether an SAg is functionally detectable in peripheral blood mononuclear cells (PBMC) from monozygotic twins discordant for HIV infection.

DESIGN AND METHODS

The V beta selective T-cell depletion found in minor lymphocyte stimulation (Mls)-positive mice is caused by an SAg encoded by the mouse mammary tumour virus. Mls is a locus whose gene product stimulates a mixed lymphocyte reaction (MLR) in mice strains identical at the major histocompatibility complex locus. If an SAg is present in PBMC and/or sorted CD4+ cells from one HIV-infected monozygotic twin, it would stimulate PBMC from the corresponding healthy monozygotic twin in an MLR. In addition, if an SAg causes V beta-selective T-cell depletion in AIDS patients, a differential proliferation to a panel of staphylococcal enterotoxins (SE) of T lymphocytes from healthy and HIV-infected monozygotic twins should become measurable.

RESULTS

No positive MLR or significant differences in the SE-driven proliferation between the healthy and the HIV-infected twins were observed.

CONCLUSIONS

Our results suggest that PBMC from the two HIV-infected twins do not express a functionally detectable SAg.

Functional analysis of two tetanus toxin universal T cell epitopes in their interaction with DR1101 and DR1104 alleles

In this study we have investigated the interaction between two DR11 alleles (DB*1101 and DB*1104) and two previously described tetanus toxin (tt) universal T cell epitopes P2(tt830-843) and P30(tt947-967) by means of a functional cytotoxic competition assay. Both truncation analysis and single alanine substitution analysis were performed. In addition, the capacity of truncated and single alanine substituted peptides to be recognized by human T cell clones from donors bearing the DR1101 or DR1104 alleles was assessed. In the case of truncated peptides the same binding and recognition pattern was observed with both alleles. Longer peptides were better competitors and more potent stimulators, a result that should be taken into account when these peptides are used as immunogens. None of the single alanine substitutions could abrogate or strongly diminish the inhibitory capacity of the analogues tested indicating the lack of strong "anchor residues" present in P2 and P30 and implicated in DR binding. In addition, although the original peptide sequences were presented to specific T cell clones with comparable efficiency, some of the alanine single substituted peptides were better recognized in association with one of the alleles by clones derived from individuals bearing the homologous allele. The only exception was the tt951-967 analogue ttW955A, which was preferentially recognized in association with the DR1104 allele regardless of the clone tested. This suggests that, although it binds to both alleles with comparable efficiency, the MHC-peptide complex so formed is conformationally distinguishable by specific T cell clones.

Functional analysis of two tetanus toxin universal T cell epitopes in their interaction with DR1101 and DR1104 alleles

In this study we have investigated the interaction between two DR11 alleles (DB*1101 and DB*1104) and two previously described tetanus toxin (tt) universal T cell epitopes P2(tt830-843) and P30(tt947-967) by means of a functional cytotoxic competition assay. Both truncation analysis and single alanine substitution analysis were performed. In addition, the capacity of truncated and single alanine substituted peptides to be recognized by human T cell clones from donors bearing the DR1101 or DR1104 alleles was assessed. In the case of truncated peptides the same binding and recognition pattern was observed with both alleles. Longer peptides were better competitors and more potent stimulators, a result that should be taken into account when these peptides are used as immunogens. None of the single alanine substitutions could abrogate or strongly diminish the inhibitory capacity of the analogues tested indicating the lack of strong "anchor residues" present in P2 and P30 and implicated in DR binding. In addition, although the original peptide sequences were presented to specific T cell clones with comparable efficiency, some of the alanine single substituted peptides were better recognized in association with one of the alleles by clones derived from individuals bearing the homologous allele. The only exception was the tt951-967 analogue ttW955A, which was preferentially recognized in association with the DR1104 allele regardless of the clone tested. This suggests that, although it binds to both alleles with comparable efficiency, the MHC-peptide complex so formed is conformationally distinguishable by specific T cell clones.

Incidence of hepatitis B virus infection among an Italian military population: evidence of low infection spread

In 1990, a prospective serological survey to estimate the rate of clinical and inapparent infection with hepatitis B virus was performed in a cohort of 1324 soldiers, 18-24 years old, during an eight-month period in Italy. At the time of enrollment the prevalence of hepatitis B markers was 4.6% (0.7% subjects positive for hepatitis B surface antigen [HBsAg], 3.0% positive for antibody to hepatitis B surface antigen [anti-HBs], and 0.9% positive for antibody to hepatitis B core antigen [anti-HBc] alone. Among the 1263 susceptible subjects who were followed-up, only 2 (0.24/100 person-years of exposure) had seroconversion for HBV markers, none of which was associated with clinical illness. Among the 9 subjects HBsAg-positive at the time of enrollment, 1 (11.2%) had lost HBsAg at the end of follow-up. These data show a low spread of HBV infection among Italian young generations.

Incidence of hepatitis A virus infection among an Italian military population

In 1990, a prospective serological survey to estimate the rate of clinical and inapparent infection with hepatitis A virus (HAV) was performed in a cohort of 1,268 soldiers, 18-24 years old, during an 8 month period in the Campania region in Italy. At the time of enrollment 318 (25%) of the 1,268 soldiers were positive for total antibodies to HAV (anti-HAV). None of them was positive for IgM anti-HAV. Among the 950 susceptible subjects who were followed up for 8 months, eight (0.8%) later seroconverted to anti-HAV positivity. This figure corresponds to an incidence of 1.3/100 person/years (eight seroconversions during 633.3 years of observation). There were two clinical (with presence of IgM-anti-HAV) and six inapparent infections. The clinical/subclinical HAV ratio was 1:3. These findings indicate that the risk of HAV infection among soldiers residing in this area is not negligible.

Evaluation of the overall degree of sensitization to airborne allergens by a single serologic test: implications for epidemiologic studies of allergy

In most epidemiologic studies of respiratory allergy, the overall degree of sensitization is usually measured by indices based on skin prick test reactions to a panel of relevant airborne allergens. In the present study we used a single assay (CAP-Phadiatop, Pharmacia, Uppsala, Sweden), which is based on the reaction between serum-specific IgE and a mixture of locally relevant inhalant allergens to measure the degree of sensitization to inhalants in the sera of 1815 young Italian men, in whom a complete diagnostic workup for respiratory allergy was performed in parallel. The intensity of reaction in the CAP-Phadiatop assay was highly correlated with: (1) an allergy index (p < 0.005), based on skin prick test reactivity to seven relevant inhalant allergens (Dermatophagoides pteronyssinus, mixed grass pollens, cat epithelium, Parietaria judaica, Olea europaea, Artemisia vulgaris, Alternaria tenuis); (2) the concentration of specific IgE to the same allergens, measured by CAP-RAST (p < 0.001), in both monosensitized and polysensitized subjects; (3) the rate of respiratory allergic diseases (p < 0.0001). Therefore CAP-Phadiatop intensity of reaction is a reliable indicator of the overall degree of sensitization to inhalant allergens. Furthermore, as demonstrated by relative operating characteristic analysis, it has an acceptable detectability power in identifying subjects with symptomatic expression of the atopy status [P(A) = 0.948]. The evaluation of the degree of sensitization to inhalants by a single and semiautomated assay represents a step forward in the standardization of procedures for epidemiologic studies of inhalant allergic diseases and for mass screening programs, which are aimed at identifying predictive markers of disease susceptibility.

The changing epidemiology of hepatitis A in Italy

In 1990, the prevalence of antibodies to hepatitis A virus infection (anti-HAV) was assayed by the ELISA method on a national sample of 1000 recruits aged 18-24 years. The overall prevalence was 29.4% (22.4% in the northern and central regions, 32.2% in the south and islands; p < 0.01). Compared with a similar study conducted in 1981, the results show a marked reduction in anti-HAV prevalence (from 66.3% to 29.4%; p < 0.01). These findings reflect the improved sanitation standards in Italy and indicate that the proportion of non-immune adults is increasing, with a higher risk of symptomatic infection in the near future.

Antibody response to meningococcal polysaccharides A and C in patients with complement defects

Patients with defects of terminal complement components are particularly exposed to the risk of developing neisserial infections and seem to respond poorly to meningococcal capsular polysaccharide (PS) C via natural immunization. The sole meningococcal PSC is, on the other hand, an excellent immunogen in normal people. Considering the great importance of vaccine prophylaxis for the prevention of meningococcal infections in patients with complement defects, it is crucial to study the antibody response to the sole meningococcal PS in these patients. We therefore analysed the levels of anti-PSA and PSC antibodies in the members of four families including patients with homozygous and heterozygous defects of C7, C8 or factor H, before and after vaccination with the sole PSA + C. Surprisingly, we found the highest levels of antibodies before vaccination in homozygous subjects, followed by heterozygous and normal controls, whereas, after vaccination, homozygous subjects showed the lowest increase of specific antibodies, indicating their relative incapability to respond to sole meningococcal PS. In conclusion, this study demonstrates (1) the capacity to respond to meningococcal PS via natural immunization by patients with total complement defects, and (2) the low responsiveness to meningococcal PS via vaccine immunization by the same patients. We propose that vaccination should be given to patients lacking specific antibodies and their serological response should be assessed. In addition this study confirms previous observations on a likely lower immunogenic power of meningococcal serogroup C via natural immunization compared with the better immunogenicity of the sole PSC.

Clinical and immunological response to typhoid vaccination with parenteral or oral vaccines in two groups of 30 recruits

The clinical and immunological responses to typhoid vaccination with parenteral and oral vaccines in two groups of 30 adult male subjects were studied. Specific anti-Salmonella typhi cell-mediated immunity and total or specific anti-lipopolysaccharide faecal immunoglobulin (Ig) A titres in vaccinated subjects were monitored. Cellular antibacterial activity was significantly increased only in orally vaccinated subjects. Serum arming activity and inhibition experiments suggested an IgA-dependent cellular cytotoxicity in those orally vaccinated. In these subjects, a total and anti-lipopolysaccharide faecal IgA increase was observed lasting up to 8 months after completion of the vaccination schedule. In parenteral vaccinated subjects, an early onset transitory increase of IgM rheumatoid factor was observed. Oral vaccine was well tolerated and free of side effects, whereas 65% of parenterally vaccinated subjects reported side effects such as fever, headache, malaise and local tenderness in the injection site.