FIG 3.

Loss of protection is associated with increased bacterial growth and liver injury. Groups of three to six C57BL/6 mice were treated as described for Fig. 1 with CoPP or vehicle, followed by intranasal infection with Y. pestis CO92. (A) Bacterial titer in the lungs and liver at 72 hpi. The bars indicate the median, and the horizontal dashed line represents the limit of detection. The numbers of mice with undetectable bacteria are indicated beneath (n = 10 per group, collected in two independent trials). (B) Liver function enzymes alkaline phosphatase (ALP), aspartate amino transferase (AST), and alanine amino transferase (ALT) were measured in the blood at 72 hpi. The data shown were collected in four independent trials (n = 20 to 22 per group) and depict the means of all the trials with the standard deviations. The gray boxes indicate the normal range for C57BL/6 mice. (C and D) Formalin-fixed lungs and liver samples were prepared at 72 hpi and processed for histopathology. (C) Representative images from CoPP-treated mice. (Left side, lungs) The upper panel represents mild to moderate inflammatory pathology found in most animals in this group, and the lower panel is the severe lesion found in one animal in this group showing neutrophil congestion, alveolar necrosis, and bacterial growth typical of primary pneumonic plague. (Right side, liver) Representative images found in the CoPP treatment group showing mild inflammatory lesions. (D) Mean severity score of lung pathology. The bars indicate the standard deviations. The data shown were collected in two independent trials and were analyzed for statistical significance by the Mann-Whitney (A) or unpaired t test (B and D) comparing treated to untreated (*, P < 0.05).