PECAM1 and infection: Isolation of CD4+CD45RA+ T cells from neonates, infants, children, and adults which had no history of recurrent infections or inflammations revealed routinely >99,4% CD31+ cells (adults >98,6%) and showed similar results as FACS sorted CD4+CD45RA+CCR7+ T cells (data not shown, Fig. S2), and were therefore considered having a naïve phenotype (Figs 1–5).