A Prevalent CXCR3+ Phenotype of Circulating Follicular Helper T Cells Indicates Humoral Dysregulation in Children with Down Syndrome

: Patients with Down syndrome (DS) are characterized by increased susceptibility to autoimmunity and respiratory tract infections that are suggestive of humoral immunity impairment. Here, we sought to determine the follicular helper (Tfh) and follicular regulatory (Tfr) T cell profile in the blood of children with DS. Blood was collected from 24 children with DS, nine of which had autoimmune diseases. Children with DS showed skewed Tfh differentiation towards the CXCR3+ phenotype: Tfh1 and Tfh1/17 subsets were increased, while Tfh2 and Tfh17 subsets were reduced. While no differences in the percentage of Tfr cells were seen, the ratio of Tfh1 and CXCR3+PD-1+ subsets to Tfr cells was significantly increased in the affected children. The excessive polarization towards a CXCR3+ phenotype in children with DS suggests that re-calibration of Tfh subset skewing could potentially offer new therapeutic opportunities for these patients.