J. Goldblatt

Association of polymorphisms within the tumour necrosis factor (TNF) genes and childhood asthma

Tumour necrosis factor alpha (TNFα) is a potent modulator of immune and inflammatory responses, and has been implicated in a variety of autoimmune diseases, including asthma. Increased levels of TNFα have been detected in both sputa and bronchoalveolar lavage fluid of asthmatic subjects during acute attacks. Interindividual variation in TNFα levels may be genetically determined and polymorphisms within the TNF genes and nearby HLA Class II region have been associated with differences in TNFα production. Objective To investigate the association of differences in asthma‐related phenotypes with two biallelic polymorphisms: a G to A substitution at position −308 of the TNFα gene promoter (TNF1 and TNF2 alleles) and an NcoI polymorphism in the first intron of the lymphotoxin alpha gene (LT‐α*1 and LT‐α*2 alleles).

A POLYMORPHISM OF THE CC16 GENE IS ASSOCIATED WITH AN INCREASED RISK OF ASTHMA

Several quantitative traits associated with the asthma phenotype have been linked to markers on chromosome 11q13, although the gene responsible has yet to be well established. The gene for Clara cell secretory protein (CC16) is an ideal candidate for involvement in an inherited predisposition to asthma because of its chromosomal location, the role of the CC16 protein in controlling airway inflammation, and differences in levels of the protein between asthmatics and healthy controls. All three CC16 exons were screened in an unselected population of 266 subjects from 76 families and a cohort of 52 severely asthmatic children. A combination of single strand conformational polymorphism (SSCP) analysis, heteroduplex analysis, DNA sequencing, and restriction digestion was used. Mutation detection methods identified an adenine to guanine substitution in the CC16 gene at position 38 (A38G) downstream from the transcription initiation site within the non-coding region of exon 1. In the unselected population, 43.6% were homozygous for the polymorphic sequence (38GG) and 46.2% were heterozygous (38AG). All the asthmatic and unaffected children from both populations were selected for an unmatched case control analysis consisting of 67 asthmatic and 46 unaffected subjects. Those homozygous for the published sequence (38AA) had a 6.9-fold increased risk of developing asthma (p=0.049) and heterozygotes (38AG) a 4.2-fold increased risk (p=0.028). Modelling of genotype as a continuous covariate indicated evidence of a significant linear trend across the three genotypes (odds ratio=2.84 per unit increase in genotype code, p=0.018). These associations were independent of age, gender, and tobacco smoke exposure. These data and the known anti-inflammatory role of CC16 in the respiratory tract suggest that alteration to the gene at position 38 may contribute to asthma.

Human Rhinovirus Species C Infection in Young Children with Acute Wheeze Is Associated with Increased Acute Respiratory Hospital Admissions

RATIONALEnHuman rhinovirus species C (HRV-C) is the most common cause of acute wheezing exacerbations in young children presenting to hospital, but its impact on subsequent respiratory illnesses has not been defined.nnnOBJECTIVESnTo determine whether acute wheezing exacerbations due to HRV-C are associated with increased hospital attendances due to acute respiratory illnesses (ARIs).nnnMETHODSnClinical information and nasal samples were collected prospectively from 197 children less than 5 years of age, presenting to hospital with an acute wheezing episode. Information on hospital attendances with an ARI before and after recruitment was subsequently obtained.nnnMEASUREMENTS AND MAIN RESULTSnHRV was the most common virus identified at recruitment (n = 135 [68.5%]). From the 120 (88.9%) samples that underwent typing, HRV-C was the most common HRV species identified, present in 81 (67.5%) samples. Children with an HRV-related wheezing illness had an increased risk of readmission with an ARI (relative risk, 3.44; 95% confidence interval, 1.17-10.17; P = 0.03) compared with those infected with any other virus. HRV-C, compared with any other virus, was associated with an increased risk of a respiratory hospital admission before (49.4% vs. 27.3%, respectively; P = 0.004) and within 12 months (34.6% vs. 17.0%; P = 0.01) of recruitment. Risk for subsequent ARI admissions was further increased in atopic subjects (relative risk, 6.82; 95% confidence interval, 2.16-21.55; P = 0.001). Admission risks were not increased for other HRV species.nnnCONCLUSIONSnHRV-C-related wheezing illnesses were associated with an increased risk of prior and subsequent hospital respiratory admissions. These associations are consistent with HRV-C causing recurrent severe wheezing illnesses in children who are more susceptible to ARIs.

Evolutionary adaptation of inflammatory immune responses in human beings

Modern mans ancestors lived in an environment where infectious, tropical diseases would have been endemic. We postulate that this relatively hostile environment would have caused genetic selection for increased proinflammatory immune responses. On migrating to temperate regions, pronounced proinflammatory responses would have been less important and selected against due to increased mortality from overly vigorous responses to harmless environmental agents. This hypothesis is supported by the observation that proinflammatory alleles in several genes involved in inflammation are more prevalent in populations with long-term tropical ancestry than those with long-term residence in temperate regions. In addition, when the former populations relocate from a tropical to a temperate region, they have a higher incidence of allergic inflammatory diseases than the latter populations. These observations suggest that there may be general patterns of recent evolutionary adaptation of the human immune system to particular regions and that these adaptations can produce differences in disease susceptibility.

Polymorphisms in the β2‐adrenoreceptor gene are associated with decreased airway responsiveness

There are a number of candidate genes thought to play a role in the development of asthma. Polymorphisms at amino acid positions 16 (arginine to glycine) and 27 (glutamine to glutamic acid) of the β2‐adrenoreceptor (B2AR) gene are known to be functionally relevant and have been associated with more severe forms of asthma, nocturnal asthma and decreased airway responsiveness in asthmatic subjects.

Associations between postnatal weight gain, change in postnatal pulmonary function, formula feeding and early asthma

Background: A study was undertaken to examine factors that might influence lung function during infancy and to test the hypothesis that change in weight during infancy is negatively associated with change in lung function. Methods: Weight, length and maximal flow at functional residual capacity (V′maxFRC) were measured at ages 1 and 12 months. V′maxFRC was adjusted for length. Asthma symptoms and age at introduction of formula feeds were identified from questionnaires. Groups were dichotomised by V′maxFRC at 1 month and change in V′maxFRC. Results: 154 infants were assessed at ages 1 and 12 months. The change in V′maxFRC was inversely associated with change in weight (ru200a=u200a−0.18, r2u200a=u200a0.13, p<0.001). The group with lower V′maxFRC at 1 month and reduced change in V′maxFRC over infancy had the greatest weight gain (pu200a=u200a0.003) and increased risk for asthma symptoms by 3 years (pu200a=u200a0.017) but not afterwards. Exclusive breast feeding to 6 months was associated with a mean reduction in weight gain at age 12 months in comparison with earlier introduction of formula milk (mean difference 0.65 kg, pu200a=u200a0.001), and was also associated with reduced asthma symptoms at 3 years (odds ratio 0.44, pu200a=u200a0.043) but not at 6 or 11 years of age. Conclusions: Weight gain in infancy is inversely associated with change in lung function during infancy. Postnatal weight gain may be indirectly associated with early transient asthma symptoms via an influence on lung growth during infancy, and this is potentially modifiable by breast feeding. These associations could be relevant to the clinically recognised syndrome of the “fat happy wheezer”.

PARASITE INFECTIONS AND THE RISK OF ASTHMA AND ATOPY

12 Since parasitic infection is endemic in the majority of the world’s population,the relationship between helminthic infection and the IgE response is highly relevant to the understanding of allergic diseases. There is a general consensus that IgE antibody is an important component of the immune resistance to helminthiasis, 5‐9 although some conflicting results have been obtained. 34 Local IgE reactions can create unfavourable conditions in the gut for intestinal parasites, and IgE can mediate the cytotoxic activity of eosinophils against parasitic larvae. These observations have led to the concept that, from an evolutionary perspective, the primary function of the allergic response may be as part of an anti-parasitic protective mechanism, and allergic disease may be the undesirable reaction towards otherwise inoVensive environmental substances. 10

Association of polymorphisms in the β2-adrenoreceptor gene with higher levels of parasitic infection

Abstract The diminishing incidence of parasitic infection in westernised societies has been suggested to result in an increased prevalance of asthma. Asthma is a polygenic disease and genome screens have shown that genes on chromosome 5q31–33 are strongly linked to the disease. The gene for the β2-adrenoreceptor is located in this region and two polymorphisms have been identified that result in amino acid changes at positions 16 (ArgGly) and 27 (GlnGlu). To determine whether these polymorphisms influence asthma and parasitic infection, a genotype/phenotype study has been performed on a cohort of 126 children from Coche Island in Venezuela. There is a high incidence of asthma on the island and intestinal helminthiasis is endemic. Genotyping for both polymorphisms was carried out by using the polymerase chain reaction and allele-specific oligonucleotide hybridisation. Genotype frequencies in this cohort were consistent with other studies and both polymorphisms were in significant linkage disequilibrium. Individuals who were homozygous for Arg16 had significantly higher levels of specific IgE to Ascaris lumbricoides (P=0.002), significantly higher A. lumbricoides egg counts (P=0.001) and significantly larger wheal sizes following skin-prick testing with A. lumbricoides allergen (P=0.008). There was no association between either polymorphism and total serum IgE or asthma in this population. A combination of mast cell degranulation and the lung migratory phase of A. lumbricoides larvae may result in bronchoconstriction in infected individuals. These results suggest that the Gly 16 allele confers resistance to high levels of parasitic infection in this population. An alternative explanation for the association is that it may be the result of linkage disequilibrium with other genes in the chromosome 5q31–33 region.

Mutation screening of interferon‐gamma (IFNγ) as a candidate gene for asthma

Background Reduced levels of interferon gamma (IFNγ) mRNA and protein have been detected in the bronchoalveolar lavage fluid of atopic asthmatics. IFNγ is secreted by TH1 cells while IL‐4 and IL‐5 are secreted by TH2 cells and an imbalance in the TH1/TH2 response may be responsible for atopic asthma. The gene for IFN4gM is located on chromosome 12; a region of the genome which has been shown in linkage studies to be associated with asthma.

Association of CD14 promoter polymorphism with otitis media and pneumococcal vaccine responses.

Innate immunity is of particular importance for protection against infection during early life, when adaptive immune responses are immature. CD14 plays key roles in innate immunity, including in defense against pathogens associated with otitis media, a major pediatric health care issue. The T allele of the CD14 C-159T polymorphism has been associated with increased serum CD14 levels. Our objective was to investigate the hypothesis that the CD14 C-159T allele is protective against recurrent acute otitis media in children. The association between the CD14 promoter genotype and the number of acute otitis media episodes was evaluated both retrospectively and prospectively in a cohort of 300 children. Serotype-specific immunoglobulin G (IgG) antibody responses after pneumococcal vaccinations were examined according to CD14 genotype to compare immune responsiveness across genotypes. An age-dependent association was found: compared with that for CC homozygotes aged between 12 to 24 months, TT homozygotes had fewer episodes of acute otitis media (79 versus 41%, respectively; P = 0.004); this relationship was absent in older children. Additionally, TT homozygotes showed higher serotype-specific anti-pneumococcal IgG antibody levels. Our data suggest that genetic variation in CD14, a molecule at the interface of innate and adaptive immune responses, plays a key role in the defense against middle ear disease in childhood and in pneumococcal vaccine responsiveness. These findings are likely to be important to these and other immune-mediated outcomes in early life.