The mouse-adapted A/PR8, known to be highly pathogenic in mice, caused an ∼800-fold, and the highly pathogenic avian H5N1 IV A/Thailand/KAN-1/04, which causes severe pneumonia in mice [38], induced an ∼200-fold peak increase in TRAIL expression, whereas infection with the lower pathogenic ×31 stimulated by only ∼8-fold. Here, TNFSF10 is linked to susceptibility to pneumonia measurement.