Effects Of Quorum Sensing Systems On Regulatory T Cells In Catheter-related Pseudomonas Aeruginosa Biofilm Infection Rat Models

Objective: To explore the effects of QS systems on Tregs in catheter-related Pseudomonas aeruginosa(P.a) biofilm(BF) infection rat models.Methods: SD rats were divided into 4 groups randomly: PAO1 group,△las R△rhl R group, ?las I?rhl I group and control group(with sterile tube intubation as control). The rats of tube associated lung infection model caused by Pseudomonas aeruginosa with BF formation was established by planting a BF covered tube into the trchea. The rats were sacrificed on the7 th day after intubation. Lung tissue Colony forming units(CFU),pathological changes of lungs, total cell counts in bronchoalveolar lavage fluid(BALF), the level of Foxp3, TGF-β1, IL-10 in PAO1 strain group were examined and compared with the QS-mutant ?las R?rhl R and?las I?rhl I groups.Results:(1)The bacterial counts were significant higher in PAO1,△las R△rhl R and ?las I?rhl I groups than that in sterile controlgroup(p<0.05),and the counts were obviously higher in PAO1group(3.95±0.25)than that in △las R△rhl R group(2.91±0.28) and?las I?rhl I group(3.04±0.32, p<0.05). No significant difference was observed between the two QS-mutant groups(p>0.05).(2)There was no obvious pathological changes in lung tissue in sterile control group,while the bronchi and blood vessels in the PAO1 group were infiltrated by a large number of inflammatory cells and complicated with alveolar septum thickening and local abscess and necrosis. The pathological changes were milder in △las R△rhl R group and ?las I?rhl I group than in PAO1 group.No significant difference was observed between the two QS-mutant groups.(3)The total BALF inflammatory cell counts were significant higher in PAO1 group,△las R△rhl R group and ?las I?rhl I group than that in sterile control group( p< 0.05),and the cell counts were obviously higher in PAO1 group(3.19±0.16 *106 /ml) than that in △las R△rhl R group(2.34±0.28 *106 /ml)and ?las I?rhl I group(2.13±0.42 *106 /ml,p<0.05). No significant difference was observed between the two QS-mutant groups(p>0.05).(4)The expressions of Foxp3 m RNA were higher in the three infected groups than that in sterile control group(0.65±0.32, p< 0.05), and it was significant higher in PAO1 group(4.62±1.07) than in △las R△rhl R group(2.15±1.43) and ?las I?rhl I group(2.40±1.28,p<0.05). No significant difference was observed between the two QS-mutant groups(p>0.05).(5)The accumulated optical density valueof TGF-a1 were significant higher in the three infected groups than in sterile control group(3721.66±1412.95,p<0.05), and significant higher in PAO1 group(65090.56±33956.54) than that in △las R△rhl R group(28861.99 ± 10826.96)and ?las I?rhl I group(29741.07±8315.91,p<0.05).No significant difference was observed between the two QS-mutant groups(p>0.05).(6)The level of IL- 10 were higher in the three groups than in sterile control group(57.43 ± 22.13 ng/ml), and significant higher in PAO1group(188.07±57.01)than that in △las R△rhl R group(93.31 ±17.26 ng/ml)and ?las I?rhl I group(91.67±18.28 ng/ml, p<0.05).No significant difference was observed between the two QS-mutant groups(p>0.05).Conclusion: Pseudomonas aeruginosa QS systems can trigger host immune system, accompanied with the up-regulation of Foxp3 expression and increase the TGF-β1 and IL-10 levels in lung tissue, which may prompt the protraction and persistence of infection.