PECAM1 and HIV-1 infection: Based on the correlation between TREC levels and CD31 expression (Figure 3B), we performed a cross-sectional analysis of CD31 expression levels on naïve CD31+ CD4+ T-cells from older vs. younger SN and HIV-1 infected age matched adults, but did not find a diminution of the CD31 relative fluorescence intensity that would be consistent with extensive cellular turnover during aging or HIV-1 infection (data not shown).