Random allergen-specific IgE expression in atopic families: evidence for inherited "stochastic bias" in adverse immune response development to non-infectious antigens

The innate response to peanut extract in ovine afferent lymph and its correlation with allergen sensitisation

The innate response generated after initial allergen exposure is crucial for polarising adaptive immunity, but little is known about how it drives an atopic or type-2 immune response. The present study characterises the response of skin-draining afferent lymph in sheep following injection with peanut (PN) extract in the presence or absence of aluminium hydroxide (AlOH) adjuvant. Lymph was collected and innate cell populations characterised over an 84 h time period. The innate response to PN extract in afferent lymph displayed an early increase in neutrophils and monocytes without any changes in the dendritic cell (DC) population. PN antigen was transported by neutrophils and monocytes for the first 36 h, after which time DCs were the major antigen trafficking cells. AlOH adjuvant gradually increased antigen uptake by DCs at the later time points. Following lymphatic characterisation, sheep were sensitised with PN extract by three subcutaneous injections of PN in AlOH, and the level of PN-specific immunoglobulin E (IgE) was determined. Sheep with higher levels of steady-state DCs in afferent lymph showed increased monocytic recruitment in afferent lymph and reduced PN-specific IgE following sensitisation. In addition, DCs from afferent lymph that had ingested PN antigen increased the expression of monocyte chemoattractant mRNA. The results of this study show that the innate response to PN extract involves a dynamic change in cell populations in the afferent lymph over time. In addition, DCs may determine the strength of the initial inflammatory cell response, which in turn may determine the nature of the antigen-specific adaptive response.

The Peri/Postnatal Epigenetic Twins Study (PETS)

The Peri/postnatal Epigenetic Twins Study (PETS) is a longitudinal cohort of 250 pairs of Australian twins and their mothers, who were recruited mid-way through pregnancy from January 2007 to September 2009. The study is centered on the developmental origins of health and disease paradigm (DOHaD) in which an adverse intrauterine environment predisposes the individual to complex disease in later life by reducing growth in utero and adversely altering developmental plasticity. Data concerning diet and lifestyle were collected from mothers during pregnancy, and samples of plasma and serum taken at 28 weeks’ gestation. We attended 75% of all births, at which time we collected multiple biological samples including placenta, cord blood, and neonatal cheek cells, the latter from 91% of pairs. Chorionicity was recorded and zygosity was determined by DNA testing where necessary. Approximately 40% of the twins are monozygotic, two-thirds of which are dichorionic. Twins were seen again at 18 months of age and repeat blood and cheek swabs taken where possible. Studies of gene expression and the epigenetic marks of DNA methylation have so far revealed that twins exhibit a wide range of epigenetic discordance at birth, that one-third of the epigenome changes significantly between birth and 18 months; shared (maternal) environment, genetic factors, and non-shared intrauterine environment contribute to an increasing proportion of epigenetic variation at birth, respectively, and affect tissues differently, and that within-pair birth weight discordance correlates with epigenetic discordance in genes associated with lipid metabolism, supporting an epigenetic mechanism for DOHaD.

Familial aggregation of allergen-specific sensitization and asthma

BACKGROUND

Familial aggregation of specific response to allergens and asthma adjusted for age and sensitization to multiple allergens was assessed in two large population cohorts.

METHODS

Allergen skin prick tests (SPTs) were administered to 1151 families in the Tucson Children's Respiratory Study (CRS) and 435 families in the Tucson Epidemiological Study of Airway Obstructive Disease (TESAOD). Sensitization was defined by wheal size ≥3 mm; physician-diagnosed asthma at age ≥8 yr was based on questionnaires. Using S.A.G.E. 6.1 software ASSOC and FCOR, familial correlations of crude and adjusted phenotypes were evaluated.

RESULTS

Crude estimates of parent-offspring (P-O) and sibling correlations were statistically significant for most allergens, ranging from 0.03 to 0.29. After adjusting for age of assessment and 'other atopy' (SPT-positive response to additional allergens), correlations were reduced by 14-71%. Sibling correlations for specific response to allergens were consistently higher than P-O correlations, but this difference was significant only for dust mite and weed mix in the TESAOD population. Familial correlation for atopic status (any positive SPTs vs. none) tended to be higher than for specific allergens. Asthma, with and without adjustment, showed greater familial correlation than either specific or general SPT response and significantly higher sibling correlation in TESAOD than in CRS, probably due to the older age of the siblings and the longer period of ascertainment.

CONCLUSIONS

Significant familial aggregation of specific response to allergen after adjustment for other atopy appears to reflect a genetic propensity toward atopy, dependent on shared familial exposures. Results also suggest that inheritance of asthma is independent of atopic sensitization.

Search for quantitative trait loci of atopy-associated immune responses using allergen-specific IgG1 as an "endophenotype"

Inherited atopic diseases of humans arise from adverse adaptive humoral responses to noninfectious environmental allergens. We previously reported that allergen-specific IgG1 provides more reliable heritability estimates for responses to allergens than total IgE. Genome scans were done for 91 Caucasian nuclear families with history of atopy for total IgE and IgG1 produced against a common major allergen from house dust mite, Der p 1. Suggestive associations for Der p 1-IgG1 production were found at 7 quantitative trait loci (QTL) (logarithm of the odds, LOD > or = 1.23; p < or = 0.009) with QTL-specific heritabilities of 73%-80%. Scans using total IgE found suggestive associations for 12 QTLs (LOD > or = 1.44; p < or = 0.004), but QTL-specific heritabilities only in the range of 30%-35%. Allergen-specific IgG1 is a suitable "endophenotype" to be used in searches for genes associated with atopy-associated humoral immune responses to common aeroallergens.