Accumulation of monoallelic mutations in HLH-causing genes increases the risk to develop clinical manifestations of HLH. Control (black squares), Prf1−/− (open squares), Rab27a+/−Stx11+/− (AS, open gray circles), Rab27a+/−Prf1+/− (AP, gray squares), and Rab27a+/−Prf1+/−Stx11+/− mice (ASP, gray open squares) were infected with 200 PFU of LCMV-WE. (A) Survival, (B) body weight, and (C) body temperature are shown. Data (mean ± standard error of the mean [SEM]) are representative of 3 to 4 independent experiments with at least 3 mice in each group. *P < .05.