Estimating the infectivity of CCR5-tropic simian immunodeficiency virus SIV_mac251 in the gut

CD4⁺ T-cell depletion during acute human immunodeficiency virus infection occurs predominantly in the gastrointestinal mucosa. Using experimental data on SIV_mac251 viral load in blood and CD4 ⁺ T cells in the jejunum, we modeled the kinetics of CD4⁺ T-cell infection and death and estimated the viral infectivity. The infectivity of SIV_mac251 is higher than previously estimated for SHIV89.6P infection, but this higher infectivity is offset by a lower average peak viral load in SIY_mac251. Thus, the dynamics of target cell infection and death are remarkably similar between a CXCR4- and a CCR5-tropic infection in vivo.