Changes in the Messenger RNA Expression of Toll-Like Receptors 2 and 4 in Healthy Infants According to Age.

Background:  Toll-like receptors (TLRs) are potentially useful indicators of several pediatric disease states. Here, we explore the mechanisms by which inflammation is regulated by interactions between microbiota and the host. Little data are available regarding the expression of TLRs in postnatal healthy infants. TLR 2 and TLR4 are extracellular TLRs that act as innate immune receptors by recognizing a wide range of endogenous ligands and microorganisms.

Methods:  The aim of this study was to use real-time polymerase chain reaction to investigate the expression of the messenger RNAs (mRNAs) of TLR2 and TLR4 in blood samples obtained from healthy full-term infants and toddlers.

Results:  We analyzed the mRNA expression levels of TLRs in 88 healthy term children separated according to age. The median expression level of TLR2 was 1.49 ± 1.10 arbitrary units (AU) (= 25) in infants younger than 3 months, 0.67 ± 0.72 AU (= 25) in infants aged between 3 and 12 months, and 0.03 ± 0.02 AU (= 38) in infants older than 12 months. The median expression level of TLR4 was 1.25 ± 0.79 AU (= 25) in infants younger than 3 months, 0.75 ± 0.54 AU (= 25) in infants aged 3 to 12 months, and 0.44 ± 0.28 AU (= 38) in infants older than 12 months. There was difference in the mRNA expression level of TLR2 and TLR4 between infants aged 0 to 3 and 3 to 12 months and those aged more than 1 year ( < 0.0001 and  < 0.0001, respectively) CONCLUSION:  We found that the expression levels of TLR2 and TLR4 were associated with age. In particular, we observed that their expression increased during the suckling period and then clearly decreased once the infants reached 1 year of age ( < 0.001). These findings could be related to microbial colonization and the immune system.