Relationship between the presence of newborn and the house dust endotoxin

The protective effect of rural life on mite sensitization disappears among urban migrants in the South of Vietnam

Background

Rapid urbanization combined with rural migration to urban areas in southern Vietnam could be risk factors for allergen sensitization, contributing to chronic respiratory diseases (CRD). We aimed to evaluate the prevalence of mite sensitization and its relation to house dust characteristics among rural and urban native and migrating populations with CRD.

Methods

Rural (n = 19) and urban (n = 46) dwellings were defined on the basis of a home typology. Controls were western Belgian houses (n = 14). Besides the house characteristics, both endotoxin and mite allergens were measured in the settled dusts. The sensitization to mite allergens was defined by positive skin prick test (SPT) and concentration of specific IgE (sIgE)≥ 0.7 U/mL. The prevalence of mite sensitization was evaluated among 610 patients with CRD and compared according to both their home types and places of birth and residences.

Results

The concentration of endotoxin (but not mite allergen) was higher in rural compared to urban dusts (440 (95%CI: 314–566) versus 170 (95%CI: 115–226) EU/mg; p < 0.0001). The prevalence of positive sIgE to Der p1 and Der p2 was significantly lower in rural (9% and 5%) compared to urban (15% and 9%) population, consistent with the positive SPT to mite (14% and 21%, respectively). Among the urban migrants, the risk of mite sensitization (SPT) was higher compared to the rural natives (OR: 1.79 (1.02–3.15), p < 0.05) and not different to the urban ones (OR: 1.35 (0.82–2.23) p NS).

Conclusion

In Vietnam, associated with higher endotoxin (but not allergen) dust concentrations, the risk of mite sensitization was lower in rural compared to the native urban population, but this protective effect could disappear among rural to urban migrants.

Early-life exposure to sibling modifies the relationship between CD14 polymorphisms and allergic sensitization

BACKGROUND

Markers of microbial exposure are thought to be associated with risk of allergic sensitization; however, the associations are inconsistent and may be related to gene-environment interactions.

OBJECTIVE

To examine the relationship between polymorphisms in the CD14 gene and allergic sensitization and whether sibling exposure, as a marker of microbial exposure, modified this relationship.

METHODS

We used data from the Tasmanian Longitudinal Health Study and the Melbourne Atopy Cohort Study. Two CD14 polymorphisms were genotyped. Allergic sensitization was defined by a positive response to a skin prick test. Sibling exposure was measured as cumulative exposure to siblings before age 6 months, 2 and 4 years. Logistic regression and multi-level mixed-effects logistic regression were used to examine the associations. Effect estimates across the cohorts were pooled using random-effects meta-analysis.

RESULTS

CD14 SNPs were not individually associated with allergic sensitization in either cohort. In TAHS, cumulative sibling exposure before age 6 months, 2 and 4 years was each associated with a reduced risk of allergic sensitization at age 45 years. A similar effect was observed in MACS. Meta-analysis across the two cohorts showed consistent evidence of an interaction between cumulative sibling exposure before 6 months and the rs5744455-SNP (P = 0.001) but not with the rs2569190-SNP (P = 0.60). The pooled meta-analysis showed that the odds of sensitization with increasing cumulative exposure to sibling before 6 months of age was 20.9% smaller in those with the rs5744455-C-allele than the T-allele (OR = 0.83 vs 1.05, respectively).

CONCLUSION AND CLINICAL RELEVANCE

Cumulative sibling exposure reduced the risk of sensitization from childhood to middle age in genetically susceptible individuals.