CASP4 and Salmonella Infections: It is tempting to speculate that the loss of GBP2 led to the expansion of GBP4 in M. Myotis and E. fuscus since, in humans, upon Salmonella infection, GBP1 requires GBP2 and GBP4 to recruit caspase-4 to the surface of the bacteria (2, 40).