Detection of basal levels of regulatory T cells
In the next series of experiments, we analyzed the number of Tregs at
baseline in the absence of antigen stimulation. We defined baseline
Tregs as the total number of CD137+CD154- T cells detected at baseline,
without any antigen stimulation 30. As expected, Tregs
defined as CD137+ were correlated with Tregs defined by the alternative
markers CD4+CD25+CD127low 38,45 (Figure
4a-b ). There was substantial variation in the number of Tregs (total
CD137+) among participants (Figure 4c ), the number of CD137+
cells varing 90-fold from 925 to 86,000 per million CD4+ T cells.
We hypothesized that the size of the baseline Treg population present in
each individual might influence their capacity to mount an
allergen-specific T cell response following stimulation with the
allergen-derived peptide pools. There was a suggestion of an inverse
correlation between the number of Tregs (CD137+ unstimulated cells) and
the number of Teff (cytokine+ CD154+ allergen-stimulated cells), but
this was not statistically significant (Figure 4d ).