Gene-environment interactions between CD14 C-260T and endotoxin exposure on Foxp3⁺ and Foxp3^- CD4⁺ lymphocyte numbers and total serum IgE levels in early childhood

Background: Innate immune system stimuli, such as endotoxin, seem to affect allergy risk. Previously, we described gene-environment interactions between the endotoxin receptor polymorphism C-260T of the CD14 gene and endotoxin exposure on total serum IgE level; however, the mechanism of this interaction is not known. Objective: To examine whether this gene-environment interaction affects early CD4⁺Foxp3^- or CD4⁺Foxp3 ⁺ lymphocyte numbers. Methods: Participating children were part of a birth cohort in the Detroit metropolitan area. Participants were genotyped for the CD14 C-260T polymorphism. Endotoxin exposure was estimated from dust measured in the home when children were 6 months old. Intracellular Foxp3 protein expression, a regulatory T-cell marker, was used to characterize CD4⁺ lymphocytes in blood samples collected at the age of 12 months; total serum IgE level was also measured at this time. Because race/ethnicity may confound or modify genetic associations, all analyses were stratified by race/ethnicity. Results: We observed a significant gene-environment interaction between CD14 C-260T genotype and endotoxin exposure on CD4⁺ lymphocyte numbers, particularly CD4⁺Foxp3^- lymphocytes. Stratified analyses suggest effect modification by race/ethnicity on CD4 ⁺Foxp3⁺ lymphocyte numbers, with a significant interaction in African American children but not in white children. The interaction between CD14 C-260T genotype and endotoxin exposure on total IgE levels was opposite that observed for CD4⁺ lymphocyte numbers, suggesting reciprocal relationships. Conclusions: A gene-environment interaction between endotoxin and CD14 C-260T genotype on IgE levels may be the result of an upstream, opposing effect on CD4⁺Foxp3⁺ and CD4⁺Foxp3^- lymphocyte numbers. Race/ethnicity may affect which of these cell populations is affected by this gene-environment interaction.