In the absence of effector proteins, the Pseudomonas aeruginosa type three secretion system needle tip complex contributes to lung injury and systemic inflammatory responses.

Herein we describe a pathogenic role for the Pseudomonas aeruginosa type three secretion system (T3SS) needle tip complex protein, PcrV, in causing lung endothelial injury. We first established a model in which P. aeruginosa wild type strain PA103 caused pneumonia-induced sepsis and distal organ dysfunction. Interestingly, a PA103 derivative strain lacking its two known secreted effectors, ExoU and ExoT [denoted PA103 (ΔU/ΔT)], also caused sepsis and modest distal organ injury whereas an isogenic PA103 strain lacking the T3SS needle tip complex assembly protein [denoted PA103 (ΔPcrV)] did not. PA103 (ΔU/ΔT) infection caused neutrophil influx into the lung parenchyma, lung endothelial injury, and distal organ injury (reminiscent of sepsis). In contrast, PA103 (ΔPcrV) infection caused nominal neutrophil infiltration and lung endothelial injury, but no distal organ injury. We further examined pathogenic mechanisms of the T3SS needle tip complex using cultured rat pulmonary microvascular endothelial cells (PMVECs) and revealed a two-phase, temporal nature of infection. At 5-hours post-inoculation (early phase infection), PA103 (ΔU/ΔT) elicited PMVEC barrier disruption via perturbation of the actin cytoskeleton and did so in a cell death-independent manner. Conversely, PA103 (ΔPcrV) infection did not elicit early phase PMVEC barrier disruption. At 24-hours post-inoculation (late phase infection), PA103 (ΔU/ΔT) induced PMVEC damage and death that displayed an apoptotic component. Although PA103 (ΔPcrV) infection induced late phase PMVEC damage and death, it did so to an attenuated extent. The PA103 (ΔU/ΔT) and PA103 (ΔPcrV) mutants grew at similar rates and were able to adhere equally to PMVECs post-inoculation indicating that the observed differences in damage and barrier disruption are likely attributable to T3SS needle tip complex-mediated pathogenic differences post host cell attachment. Together, these infection data suggest that the T3SS needle tip complex and/or another undefined secreted effector(s) are important determinants of P. aeruginosa pneumonia-induced lung endothelial barrier disruption.

Misclassification of pulmonary hypertension in adults with sickle hemoglobinopathies using Doppler echocardiography.

OBJECTIVE: To compare the diagnostic utility of Doppler echocardiography-derived tricuspid regurgitant jet velocity (TRV) ≥ 2.5 m/s to right heart catheterization (RHC) in defining pulmonary hypertension (PH) in adult patients with sickle cell disease (SCD). METHODS: This is a retrospective chart review of adults with SCD who had a TRV ≥ 2.5 m/s and RHC. A TRV ≥ 2.5 m/s is suggestive of PH. Pulmonary arterial hypertension (PAH) was defined as a mean pulmonary artery pressure (mPAP) ≥ 25 mm Hg and pulmonary capillary wedge pressure ≤ 15 mm Hg. Pulmonary venous hypertension was defined as an mPAP ≥ 25 mm Hg and pulmonary capillary wedge pressure >15 mm Hg. RESULTS: Twenty-five patients with SCD met the inclusion criteria. Nine of the 25 (36%) patients had an mPAP ≥ 25 mm Hg. Of these 9, 3 (33%) had PAH and 6 (66%) had pulmonary venous hypertension. Patients with PH did not have a higher TRV (3.1 ± 0.68 vs 2.70 ± 0.16 m/s; P = 0.12), but they did have higher cardiac outputs (10.4 ± 2.7 vs 7.81 ± 1.85 L/min; P = 0.012. The specificity of TRV equal to 2.51 m/s in diagnosing PH was 18.8%. At a TRV of 2.88 m/s, the specificity increased to 81%. CONCLUSIONS: In adults with SCD, a TRV of 2.5 m/s lacks specificity for use as a screening tool in the diagnosis of PH. Using a TRV of ≥ 2.88 m/s allows the TRV to be used as a screening tool and reduces the false-positive rate and need for unnecessary RHC.