"Bystander" amplification of PBMC cytokine responses to seasonal allergen in polysensitized atopic children

Background: Atopic children show increased expression and production of the Th2-associated cytokines IL-4, IL-5, IL-13, and IL-9 from PBMCs after stim ulation with allergen, but it has previously not been clearly determined wh ether the Th2-cytokine production is restricted to the inhalant allergen th e child is sensitized to, and whether perennial or seasonal allergens induc e different cytokine responses. Our purpose was to determine whether in vit ro Th2 cytokine production is specific to the sensitizing allergen, and to compare the cytokine responses to a perennial and a seasonal allergen in mo nosensitized and polysensitized children. Methods: Using semiquantitative RT-PCR, we analyzed the expression of the c ytokines IL-4, IL-5, IL-13, IL-9, IL-10, and IFN-gamma after stimulation of PBMCs with house-dust-mite (HDM) or ryegrass allergen. The cells were samp led from groups of 6-year-old children sensitized to either HDM (n = 20) or ryegrass (n = 24), or to both allergens (n = 20), as well as from a nonato pic group (n = 20). Results: After stimulation with HDM allergen, PBMCs from children sensitize d only to HDM expressed increased mRNA levels of the Th2 cytokines, but not of IL-10 and IFN-gamma, whereas ryegrass stimulation did not result in inc reased cytokine expression. PBMCs from children sensitized to HDM and ryegr ass expressed increased Th2 cytokines after stimulation with either of th t wo allergens. In contrast. PBMCs from children sensitized only to ryegrass did not express increased levels after stimulation with either of the aller gens. Conclusions: The expression of Th2 cytokines after in vitro stimulation of PBMCs from atopic children is specific to the sensitizing allergen, indicat ing that atopic status per se does not affect the type of T-cell response. In addition, T cells specific to seasonal allergens circulate in the blood out of season only if the child is concomitantly sensitized to a perennial allergen.