TH2‐polarized immunological memory to inhalant allergens in atopies is established during infaney and early childhood

Summary Background There is increasing evidence that the T‐cell reactivity to environmental allergens underlying expression of allergic disease in adulthood, develops initially during childhood. However, there is little information available on the kinetics of these early responses, or on the patterns of cytokine production during this period. Objective The purpose of this study was twofold: to obtain further information on the reported differences between responses to food versus inhalant allergens during early childhood, and to ascertain the age‐range over which T‐cell responses to inhalant allergens become polarized towards the TH 2 cytokine profile, in potentially atopic children. Methods In vitro cytokine responses to house dust mite (HDM) and egg (OVA) were assessed by semiquantitative RT‐PCR in panels of 2‐ and 5‐year‐old children and adults; lymphoproliferative responses to OVA were subjected to epitope analysis. Results At age 2 years IL‐4/IL‐5 responses to HDM grouped with positive atopic family history, and by age 5 years cytokine responses correlated strongly with individual SPT reactivity to HDM. In contrast, OVA responses were restricted to weak and transient IL‐5 signals in the 2‐year‐old family history positive group. Lymphoproliferation assays performed in parallel indicate a log‐scale greater postnatal expansion of T‐cell reactivity to the inhalant allergen; preliminary epitope analysis of OVA responses indicate that the number of OVA epitopes recognised decrease during early childhood. Conclusions Inhalant allergen‐specific in vitro cytokine production associated with positive skin‐prick test (SPT) reactions, one of the hallmarks of adult atopy, manifests in children at or before 5 years of age; additionally, cytokine responses in SPT negative 5 year‐olds are restricted to IFNγ, as per normal adults. In contrast, T‐cell responses to a typical food allergen appear to be deleted during early childhood.