Several of the factors mentioned above, such as a CID-like phenotype with or without a disturbed TCR signal (Picard et al., 2009; Sauer et al., 2012), cytokine disturbance (Setoguchi et al., 2005), and even persistent CD4 lymphopenia itself (Matsuoka et al., 2010) might contribute to the reduction in regulatory T cells. Here, CD4 is linked to lymphopenia.