To analyse the effects of S100A8/A9 and its counterreceptor TLR4 on platelets during acute pneumonia, we examined neutrophil recruitment in global S100A9−/− and conditional TLR4PF4Cre+ mice upon intratracheal infection with the clinically relevant pathogen K. pneumoniae. The gene discussed is TLR4; the disease is susceptibility to pneumonia measurement.