Expression of toll-like receptors and immune-regulatory markers during early infancy and allergy development in Estonian and Swedish infants

• Background: Allergies have increased during the last decades with the highest prevalences in countries with a Westernised lifestyle. As microbial activation might be required for an accurate maturation of the immune system, a reduced or altered microbial exposure during infancy has been suggested as a possible cause for the increase of allergic diseases in affluent countries. Aim: The aim of this study was to investigate the gene expression of TLR2, TLR4, Foxp3, Ebi3 and SOCS3 involved in LPS signaling pathways and immune regulation in two prospectively followed birth cohorts, one from Estonia and one from Sweden, in relation to domestic endotoxin levels and allergy development. Material and methods: Twenty-three children from Estonia and 52 from Sweden were followed from birth to five years of age regarding allergy development using questionnaires, clinical examinations and skin prick tests. RNA was isolated from unstimulated peripheral blood mononuclear cells (PBMC) in samples collected at birth, 3, 6, 12 and 24 months of age. mRNA expression of TLR2, TLR4, SOCS3, Ebi3 and Foxp3 was analysed with real-time RTPCR. The mRNA expression of the genes were compared to previously obtained data of LPS/IFN-γ induced cytokine and chemokine PBMC secretion at the corresponding time-points and also to domestic endotoxin levels. Results: The Estonian infants had higher mRNA expression of the two regulatory T cell (Treg) associated markers Foxp3 and Ebi3 at birth than the Swedish infants. The Foxp3 and Ebi3 expression correlated at all time-points. The mRNA expression of TLR2, TLR4 and SOCS3 was similar in Estonian and Swedish infants at all ages. None of the genes were associated with endotoxin levels.TLR4 mRNA expression correlated positively with cytokines that were upregulated by LPS/IFN- γ stimulation, but was negatively correlated to CCL2 secretion which was downregulated by the stimulation. Low expression of TLR2 mRNA at birth was found in Swedish children who were allergic at 5 years of age. Sensitisation up to 5 years of age was associated with low Ebi3 expression at birth. Conclusion: Estonian children are born with enhanced Ebi3 and Foxp3 expression compared to Swedish children, suggesting an increased capacity for early immune regulation among infants from a country with a low prevalence of allergic disease. An increased early capacity to respond to TLR2 ligands, i.e. Gram positive bacteria, may protect against allergy development.

Nyckelord

Regulatory T cells

TLR2

TLR4

SOCS3

foxp3

Ebi3

allergy

LPS

endotoxin

MEDICINE

MEDICIN

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