OCLN and pneumonia: It is known that exposure to tobacco smoke is a substantial risk factor for many acute respiratory bacterial infections, including pneumonia26 and meningococcal disease27, as Streptococcus pneumoniae, a pneumonia pathogen, downregulates the tight junction proteins Claudin-7 and -1028, while Neisseria meningitidis, which causes meningococcal pneumonia, disrupts occludin, another tight junction protein29.