IL21 and peeling skin syndrome: B-cell-activating Tph cells are defined as CXCR5-PD-1hi memory CD4 T cells and have been found to be increased in the blood of pSS patients [16,30,31] These cells do not express Bcl6, are PD-1hi, can co-express ICOS and secrete high levels of CXCL13 and IL-21 [9,11,32].