Pretreatment with the FXI A2 domain binding antibody, 3G3, prevented the death of baboons challenged with a lethal IV injection of heat-inactivated S aureus. Survival plot of animals challenged with an LD of heat-inactivated S aureus and pretreated with the anti-FXI A2 domain antibody 3G3 (LDSA + 3G3; n = 4) vs control animals’ LDSA in the absence of 3G3 pretreatment (n = 3). Survival distribution of the 2 groups was determined using a log-rank Mantel-Cox test; the result is significant at P = .01. LD, lethal dose; LDSA, lethal dose of S aureus.