SIVsm infection in mangabeys is associated with declines in TREC levels. TREC levels were determined by real-time PCR and presented for CD4 (A) and CD8 (B) T-cell populations in peripheral blood. Preinfection (open bars) and week 37 postinfection (closed bars) data for all 6 mangabeys are depicted. All mangabeys with and without thymuses had similar rates of TREC decline after SIVsm infection.