Neonatal innate immunity and Toll-like receptor

The innate immune response is the first line of defense against microbial infections. Innate immunity is made up of the surface barrier, cellular immunity and humoral immunity. In newborn, immunologic function and demands are different to adults. Neonatal innate immunity specifically suppresses Th1-type immune responses, and not Th2-type immune responses, which are enhanced. And the impaired response of macrophages is associated with the defective innate immunity in newborn period. Toll-like receptors (TLRs) play a key roles in the detection of invading pathogens and in the induction of innate immune responses. In newborn, the expression of TLRs is age dependent, so preterm has low expression of TLRs. Also, there are defects in signaling pathways downstream of TLRs. As a consequence, the defects of TLRs activity cause the susceptibility to infection in the neonatal period.