(1) Twelve hours after the tracheal inoculation of 108 CFU live S. haemolyticus, macroscopic evidence of lung injury was observed, histologically characterized by confluent pneumonia and associated with marked increases in TNF-α and MIP-2 and the presence of significant concentrations of S. haemolyticus in the BAL and in the lung homogenate. Here, TNF is linked to susceptibility to pneumonia measurement.