TRECs levels correlate significantly with CD4 naïve T cell numbers
To examine the correlation between T cell subsets and TRECs levels, we analyzed the absolute numbers of different T cell subsets in the 410 healthy children. There was a correlation between TRECs levels and the numbers of CD3 T cells (r 0.220, p<0.0001) (Fig. 4A) and CD4 T cells (r 0.318, p<0.0001) (Fig. 4B). We also found a significant correlation between TRECs levels and CD4+CD45RA+CD27+ (CD4 naïve) T cell numbers (r 0.305, p<0.0001) (Fig. 4C). However, there was no correlation between TRECs levels and CD8+/CD8+CD45RA+CD27+ (CD8 naïve) T cell numbers (p>0.1) (Fig. 4D/E), or between TRECs levels and CD4+/CD8+ central memory T cell or CD4/CD8 effector memory T cell numbers (Fig. 4F–H).
Because CD4 naïve T cell numbers showed a strong correlation with TRECs levels, we next analyzed the correlation between TRECs levels and CD4 naïve T cell numbers in different age groups (Fig. 5). We found significant correlations between TRECs numbers and CD4 naïve T cell numbers in the 1–4 y (r 0.243, p 0.023) (Fig. 5D) and 4–8 y (r 0.409, p<0.0001) age groups (Fig. 5E).