CLDN4 and pneumonia: The apoptosis causes the degradation of the alveolar barrier by down-regulating the expression of tight-junction proteins, especially claudin-4, that inhibit alveolar fluid clearance, In our study we also found the reduced expression of claudin-4, claudin-18, and JAMA-1, which could explain the high incidence of bacteremia incidence in patients with AKI and pneumonia.