Relationship between cytokine expression patterns and clinical outcomes: two population-based birth cohorts

BACKGROUND

Models that incorporate patterns of multiple cytokine responses to allergens, rather than individual cytokine production, may better predict sensitization and asthma.

OBJECTIVE

To characterize the patterns of peripheral blood mononuclear cells' (PBMCs) cytokine responses to house dust mite (HDM) allergens among children from two population-based birth cohorts using machine learning techniques.

METHODS

PBMCs collected at 8 years of age from the UK Manchester Asthma and Allergy Study (n = 268) and at 14 years of age from the Australian Raine Study (n = 1374) were cultured with HDM extract (10 μg/ml). Cytokine expression (IL-13, IL-5, IFN-γ, and IL10) was measured in the supernatant. Cytokine patterns were identified using a Gaussian mixture model clustering, and classification stability was assessed by bootstrapping.

RESULTS

A six-class model indicated complex latent structure of cytokine expression. Based on the characteristics of each class, we designated them as follows: 'Nonresponders' (n = 905, 55%); 'IL-10 responders' (n = 49, 3%); 'IFN-γ and IL-13 medium responders' (n = 56, 3.4%); 'IL-13 medium responders' (n = 351, 21.4%); 'IL-5 and IL-13 medium responders' (n = 77, 4.7%); and 'IL-13 and IL-5 high responders' (n = 204, 12.4%). 'IL-13 and IL-5 high responders' were at much higher risk of HDM sensitization and asthma compared to all other classes, with 88% of children assigned to this class being sensitized and 28.5% having asthma.

CONCLUSION

Using model-based clustering, we identified several distinct patterns of cytokine response to HDM and observed interplay between cytokine expression level, cytokine patterns (especially IL-13 and IL-5), and clinical outcomes. 'IL-13 and IL-5 high responders' class was strongly associated with HDM sensitization. However, among HDM-sensitized children, one-third showed no PBMC response to HDM, and the majority of HDM-sensitized children did not have asthma or wheeze. Our findings suggest that positive HDM 'allergy tests' and asthma are associated with a broad range of immunophenotypes, which may have important implications for the use of cytokine-targeted treatment approaches.

Vitamin D and atopy and asthma phenotypes in children: a longitudinal cohort study

Vitamin D has been linked in some studies with atopy- and asthma-associated phenotypes in children with established disease, but its role in disease inception at the community level is less clear. The aim of the present study was to investigate associations between vitamin D status and biological signatures indicative of allergy and asthma development in children aged 6 and 14 years in Perth, WA, Australia (latitude 32° S). Serum vitamin D was assayed in 989 6-yr-olds and 1,380 14-yr-olds from an unselected community birth cohort; 689 subjects were assessed at both ages. Vitamin D levels were assessed as a risk modifier for respiratory and allergic outcomes at both ages, using previously ascertained phenotypic data. The predictive value of vitamin D levels at age 6 yrs for development of clinical phenotypes at age 14 yrs was also examined. Serum vitamin D levels in children of both ages were negatively associated with concurrent allergic phenotypes; sex stratification revealed that this association was restricted mainly to males. Furthermore, vitamin D levels at age 6 yrs were significant predictors of subsequent atopy/asthma-associated phenotypes at age 14 yrs. In an unselected community setting, children (particularly males) with inadequate vitamin D are at increased risk of developing atopy, and subsequently bronchial hyperresponsiveness (BHR) and asthma. In a large unselected cohort, males with inadequate vitamin D at 6 and 14 yrs of age had increased atopy and BHR. Low vitamin D at age 6 yrs was a predictor of atopy and asthma at 14 yrs of age.

Th2-associated immunity to bacteria in teenagers and susceptibility to asthma

Bacterial colonisation of the airways is associated with increased risk of childhood asthma. Immunoglobulin (Ig)E against bacterial antigens has been reported in some asthmatics, suggesting a role for bacterial-specific type-2 immunity in disease pathogenesis. We aimed to investigate relationships between bacterial-specific IgE amongst teenagers and asthma susceptibility. We measured titres of IgE against Haemophilus influenzae, Streptococcus pneumoniae and Staphylococcus aureus in 1,380 teenagers, and related these to asthma symptomatology and immunophenotypes. IgE titres against S. aureus-derived enterotoxins were highest amongst atopics and were associated with asthma risk. Surprisingly, IgE titres against H. influenzae and S. pneumoniae surface antigens were higher, not stratified by atopy and independently associated with decreased asthma risk. The positive association between type-2 immunity to S. aureus and asthma phenotypes probably reflects IgE-mediated effector cell activation via enterotoxin super antigens which are secreted in soluble form. The contrasting benign nature of type-2 immunity to H. influenzae and S. pneumoniae antigens may reflect their lower availability in soluble forms that can crosslink IgE receptors. We theorise that instead they may be processed by antigen presenting cells and presented to type-2 memory cells leading to mucosal secretion of interleukin (IL)-4/IL-13, a mechanism widely recognised in other tissues to attenuate T-helper-1 associated bacterial-induced inflammation.