Since Batf3−/− mice are highly susceptible to the type II Prugniaud (Pru) strain of T. gondii (11), which has intermediate virulence, we tested infection with the highly attenuated RHΔku80Δrop5 mutant (21, 22), which lacks the key virulence factor ROP5, a polymorphic serine threonine (S/T) protein kinase secreted from rhoptries (ROP) of T. gondii. This evidence concerns the gene BATF3 and infection.