PAX5 and precursor B-cell acute lymphoblastic leukemia: Similar to Pax5+/− mice, Irf4−/− mice also spontaneously develop B-ALL with incomplete penetrance (incidence 17.5%), when stressed with bacterial compounds (such as lipopolysaccharide (LPS), an important outer membrane component of gram-negative bacteria), due to the acquisition of Jak3 mutations [34].