Different effects of endotoxin versus mite and cat allergen exposure on T-cell differentiation in infants

Background: Early exposure to bacterial endotoxin has been proposed to protect against allergy development in children. Whether endotoxin is able to direct T-cell differentiation into a predominance of type I immunity is still unresolved. Objective: We sought to compare the effects of endotoxin and mite and cat allergens on T-cell differentiation in infants. Methods: In a random population sample of 135 2-year-old children of an ongoing birth-cohort study, peripheral blood CD4(+) and CD8(+) T-cell subsets were defined by the expression of the chemokine receptors CCR5 and CCR3 as surrogate markers for type I and type 2 T cells, respectively. Endotoxin and mite and cat allergens were measured in house dust collected from the mother's mattress at the child's age of 3 months to assess early exposure. Results: In the CD4(+) T-cell subset, endotoxin levels were positively associated with high proportions of type 1 CCR5(+) cells (odds ratio for fourth exposure quartile [ORQ4], 7.68; 95% CI, 1.35-43.75), whereas cat allergen levels were associated with increased proportions of type 2 CCR3(+) cells (ORQ4, 4.07; 95% CI, 1.05-15.85). In contrast to endotoxin, allergen levels were associated with CD8+ T cells, showing an inverse relationship between mite allergen concentrations and high proportions of CCR5(+) or CCR3(+) cells (CCR5(+) cells: ORQ4, 0.14; 95% CI, 0.03-0.74; CCR3(+) cells: ORQ4, 0.16; 95% CI, 0.03-0.89) and a positive association of cat allergen levels with increased proportions of CCR5(+) cells (ORQ4, 9.24, 95% CI, 1.61-53.10), as well as CCR3(+) cells (ORQ3, 6.64; 95% CI, 1.21-36.51). Conclusion: Our results indicate that endotoxin has the potential to promote the development of type 1 CD4(+) T cells, where-as mite and cat allergens primarily modify the proportion of CD8(+) cells of both types.