SIVsm infection in mangabeys leads to early increases in plasma IL-7 levels. IL-7 levels in the plasma of 6 mangabeys. Three had thymuses (continuous lines; SM1, blue, □; SM2, turquoise, ▵; SM3, purple, ▿). Three underwent thymectomy (broken lines; SM4, green, ▴; SM5, black, •; SM6, red, ▪). Data are shown through 37 weeks of infection. All 6 mangabeys had sharp increases in IL-7 levels during the first 5 weeks of infection.