CCR9 and peeling skin syndrome: While there was a trend for increased ICOS and PD-1 expression in pSS patients compared to HC for CXCR5-expressing cells, this was only significant for PD-1/ICOS co-expression in CXCR5+CCR9- cells and ICOS expression of CXCR5+CCR9+ co-expressing cells (Figure 3A).