Abstract
The immune response that develops in early childhood underlies the development of inflammatory diseases such as asthma and there are few data from tropical Latin America (LA). This study investigated the effects of age on the development of immunity during the first 5 years of life by comparing innate and adaptive immune responses in Ecuadorian children aged 6–9 months, 22–26 months, and 48–60 months. Percentages of naïve CD4+ T cells declined with age while those of memory CD4+ and CD8+ T cells increased indicating active development of the immune system throughout the first five years. Young infants had greater innate immune responses to TLR agonists compared to older children while regulatory responses including SEB-induced IL-10 and percentages of FoxP3+ T-regulatory cells decreased with age. Enhanced innate immunity in early life may be important for host defense against pathogens but may increase the risk of immunopathology.
Highlights
The prevalence of inflammatory allergic diseases has increased in industrialized countries over recent decades [1], such diseases remain relatively rare in rural environments, in the Tropics
This maturation of the immune system was associated with a strong age-dependent down-regulation of pro-inflammatory innate immune responses during the first 5 years of life, an observation that was linked to a decline in the percentages of regulatory T cells (CD4+CD25+FoxP3+) and IL-10 production by SEBstimulated peripheral blood leukocytes
The present study investigated the relative impact of age on the development of immune responses during early childhood in urban and rural populations in the Tropics
Summary
The prevalence of inflammatory allergic diseases has increased in industrialized countries over recent decades [1], such diseases remain relatively rare in rural environments, in the Tropics. Environmental exposures are important determinants of allergic disease risk and those occurring during early life are considered to be most relevant [2]. Microbial exposures may protect against the development of allergic diseases [3,4] and mediate their effects by driving an early maturation of the innate and adaptive immune responses [5,6] that are immature at the time of birth. The progressive upregulation of TH1 function towards adult-levels may occur through stimulation of innate immunity by microbes in the environment [6]. Delayed TH1 maturation associated with a failure to down-regulate TH2 responses may contribute to the impaired regulation that underlies the development of allergic diseases such as asthma [6]
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