RIPK1 and susceptibility to pneumonia measurement: Pneumonia pathogens, such as influenza A virus (31), Streptococcus pneumoniae, and Staphylococcus aureus, as well as pathogens that cause health care-associated pneumonia, such as carbapenem-resistant Klebsiella pneumoniae and Serratia marcescens, have been shown to activate cell death through the RIPK1/RIPK3/MLKL cascade, leading to lung parenchymal necrosis.