Original article Association between CD4 CD25 T cells and atopy in ...

6 Jartti et alARTICLE IN PRESSJ ALLERGY CLIN IMMUNOLnnn 2007FIG 6. Correlations between % CD4 1 CD25 int /CD4 T cells and IL-5 (A), IL-10 (B), and IL-13 (C) production byphytohemagglutinin-stimulated PBMCs.CD4 1 CD25 1 T cells from atopic individuals could befunctionally impaired. Alternatively, CD4 1 CD25 high cellsfrom such individuals could represent a mixture of regulatoryand activated T cells: proliferative responses of thelatter population could thereby mask the effect of regulatoryT cells.In agreement with others, 18 we showed that there isoverlap in the CD25 expression of activated versus regulatoryT cells, thereby limiting the utility of this markerto distinguish specific T-cell functional subsets. The transcriptionfactor FOXP3 has been shown to be a key regulatorygene for the development and function of regulatoryCD4 1 CD25 1 T cells and is selectively expressed by thesecells. 11,12,19 Notably, although FOXP3 expression increasedwith the level of CD25, even the brightestCD4 1 CD25 1 cells contained some FOXP3 – cells.The seasonal variation in our clinical specimens suggeststhat natural exposures, perhaps related to pollen,induce CD4 1 CD25 high cells in vivo, and these CD25 highcells appear to be a mixture of activated and regulatorycells. For example, CD4 1 CD25 high cells correlated positivelywith total IgE, and inversely with CD4 1 CD25 1suppressive capacity, suggesting the presence of activatedcells. On the other hand, there was a negative correlationbetween % FOXP3/CD4 1 25 brightest cells and total IgE,suggesting a regulatory function for this cell subset.Interestingly, activation of CD4 1 CD25 – cells can induceCD25 expression in vitro, and a subset of these activatedcells synthesizes FOXP3 19,20 and has suppressive capacity.19,21 Considering these findings, we speculate that thenumber of T reg cells may increase as a consequence ofallergen exposure and subsequent T-cell activation.Furthermore, the association between pollen counts and% CD4 1 CD25 high cells was stronger in children withallergen-specific IgE, although this was not specific forpollen. It is conceivable that variations in T reg cell numberscould also be related to seasonal alterations in otherallergens. For example, house dust mite levels vary seasonallyin the midwestern United States and generallypeak in the summer. 22 In addition, there may be other immunologicallyimportant seasonal allergens that were notin our testing panel. Finally, the seasonal variation in T regcells may have also been driven by nonallergenic factors,such as exposure to seasonal infectious diseases.Additional studies are needed to confirm whether thepattern of response is truly unique in allergic versus nonallergicindividuals.The CD4 1 CD25 int T cells in our study probably representmainly activated T cells, because the percentage ofthese cells, but not CD4 1 CD25 high T cells, was associatedwith pollen sensitization in spring and strongly with T H 2cytokine (IL-5 and IL-13), but not IFN-g, responses.Previous studies to relate the number or function ofperipheral blood CD4 1 CD25 1 T cells to other atopicphenotypes such as wheezing and atopic dermatitis haveshown partly conflicting results. In subjects with atopicdermatitis, a normal or increased number of CD4 1 CD25 1T cells with normal immunosuppressive activity hasbeen reported. 23,24 In patients with asthma, increasedCD4 1 CD25 1 T cells have been reported during acute exacerbation.25,26 We found no differences in T reg functionrelated to atopy, active atopic dermatitis, or a history ofwheezing illnesses, although the number of observationswas small (n 5 22). Neither were there differences inthe percentages of CD4 1 CD25 1 subsets (n 5 151).However, boys had higher CD4 1 CD25 high T-cell countsthan girls by univariate analysis, and this suggests thatthere may be sex differences in development of T reg cellsto correspond with sex-related differences in immunologicresponses and the prevalence of atopic diseases. 27Our study has some limitations. The available bloodsample volume for the functional assay was rather small inthis study involving young children, which limited thetypes of functional assays that were feasible. Depletion ofCD4 1 CD25 1 T cells may not be an optimal method toassess suppressive function, although many studies havedone so. 3,7,10 Although the sample size of our seasonaldata is larger than previous studies assessing seasonaleffects, additional power is desirable for interaction analysisrelated to season, pollen sensitivity, and blood cellphenotype. Finally, all the study participants were fromallergic families, and additional studies are needed toevaluate these relationships in unselected populations.Although all of the children in the COAST study haveatopic family histories, there are many healthy childrenin the study with no clinical or biological evidence of