<i>P. aeruginosa</i> T3SS needle tip complex protein PcrV associates with lung injury.

<p><b>A</b>. Injured areas of the lung were prepared for histological hematoxylin/eosin analysis at 48-hours post-inoculation. Animals were inoculated with saline solution (vehicle control), with ~1 x 10⁷ CFUs of PA103 (ΔU/ΔT), or with ~1 x 10⁷ CFUs of PA103 (ΔPcrV). Lung sections imaged at 10X (top panels) and 20X (bottom panels) revealed that intratracheal instillation of PA103 (ΔU/ΔT) or PA103 (ΔPcrV) caused lung injury. Inoculation with PA103 (ΔU/ΔT) resulted in fluid accumulation around the bronchovascular bundles (vascular cuffs, arrow heads, upper panel) and lesions reminiscent of diffuse alveolar damage (arrow heads, lower panel), characterized by fluid accumulation and inflammatory cell infiltration within the air space. Inoculation with PA103 (ΔPcrV) caused collapsed air spaces, resembling atelectasis with recruitment of inflammatory cells. These histological patterns suggest that the two PA103 mutants are capable to cause lung damage/injury, although the lesions appear distinct from one another. <b>B</b>. Injured areas of the lung were prepared for histological myeloperoxidase (MPO) staining analysis to reveal the extent of neutrophil infiltration. Inoculation with PA103 (ΔU/ΔT) caused significant neutrophil recruitment compared to either vehicle control or to inoculation with PA103 (ΔPcrV). The average numbers of MPO positive cells from at least 5 independent fields of view from three different animals per condition are presented. Error bars are the standard error of the mean. The asterisks indicate a statistically significant difference (<i>P</i> < 0.05) by one-way ANOVA and Newman-Keuls <i>post-hoc</i> test. <b>C</b>. Lungs from vehicle control (saline solution) and <i>P. aeruginosa</i>-inoculated animals were isolated <i>en </i><i>bloc</i> at 48-hours post-inoculation for analysis of hydraulic permeability (K_f). Inoculation with PA103 (ΔU/ΔT) caused significant permeability increases compared to either vehicle control or to inoculation with PA103 (ΔPcrV). The average K_f values from 5 different animals per group are shown. Error bars are the standard error of the mean. The asterisks indicate a statistically significant difference (<i>P</i> < 0.05) by one-way ANOVA and Newman-Keuls <i>post-hoc</i> test.