CD31 (PECAM-1) is a marker of recent thymic emigrants among CD4+ T-cells, but not CD8+ T-cells or γδ T-cells, in HIV patients responding to ART

Some severely immunodeficient HIV patients experience poor recovery of CD4(+) T-cell counts on antiretroviral therapy (ART). Evaluation of the function of thymopoiesis in T-cell production in individual patients requires a simple marker of T-cells that have recently emigrated from the thymus. Here, we address whether expression of CD31 on CD4(+) T-cells, CD8(+) T-cells, regulatory T-cells and gamma delta T-cells correlates with other indicators of thymus function. Adult HIV-1 patients (n = 27) with nadir CD4(+) T-cell counts <100 per mu l and a sustained virological response to ART and healthy controls (n = 23) were studied. CD31 expression was assessed by flow cytometry, T-cell receptor excision circles content by real-time PCR and thymic volume by spiral computed tomography. Proportions of CD4(+) T-cells expressing CD45RA and CD31 declined with age in HIV patients (P = 0.03) and healthy controls (P<0.0001), and correlated directly with other markers of thymus function. In controls, proportions of CD8(+) T-cells expressing CD45RA and CD31 declined with age (P = 0.003) and correlated directly with some markers of thymus function, but this was not seen in HIV patients. Proportions of CD45RA(+) CD31(+) gamma delta T-cells were higher in patients than controls (P = 0.007) and did not correlate with thymus volume. In controls, proportion of gamma delta T-cells co-expressing CD45RA and CD31 increased with age (P = 0.002). These data support the use of CD31 as a marker of recent thymic origin in CD4(+) T-cells, but not CD8(+) T-cells in HIV patients receiving ART. In such patients, CD31 expression is unlikely to indicate thymic origin in gamma delta T-cells. Immunology and Cell Biology (2010) 88, 321-327; doi: 10.1038/icb.2009.108; published online 12 January 2010