ARPP21 and urinary tract infection: In Klebsiella pneumonia, the Rcs system would regulate the expression of capsule polysaccharide (CPS) by regulating the CPS-related genes; further, the Rcs system in Klebsiella pneumoniae repressed the expression of fim gene cluster, which could acts as a virulence factor that facilitates the urinary tract infection (Su et al., 2018).