The Study On Expression And Significance Of Related Cytokines Of Th17/il-17 In Severe Pneumonia Induced By Klebsiella Pneumoniae

Background: Severe pneumonia is more serious pulmonary infectious diseases caused the development of multiple organ dysfunction. According to the acquired environmental, severe pneumonia can be divided into severe community -acquired pneumonia(SCAP) and severe hospital-acquired pneumonia(SHAP). A recent epidemiological study found that the mortality of SCAP was up to 50% while the mortality of SHAP was up to 70%.In rencent years, with the increasing of high infectious risk hosts, it is still difficult to diagnose and treat severe pneumonia enve new antimicrobial agents appear. Currently the main treatment for severe pneumonia was only depended on antibiotics, mechanical ventilation, fluid support and blood purification. But the mortality of severe pneumonia still remained high even plenty of medical resource had been costed. So it is of great importance to figure out the pathogenesis of severe pneumonia and find out new therapeutic target. Recent publications suggest that the causes of severe pneumonia are relate to the uncontrolled inflammatory response which induced local inflammation to systemic inflammation, rather than simply damage by pathogens and toxins. Recently, a new Th subset called Th17, which is different from Th1 and Th2, has been identified by IL-17 (its signature cytokine). Th17 derives from natural T cell precursor-Th0 cells and plays an important role in pro-inflammatory responses and autoimmune diseases. It is also known as inflammatory T cell because of its pro-inflammatory role. IL-17A is the prototype member of IL-17 family cytokines, is a homodimer of two 155 amino acid glycoprotein with signal peptides at their N-terminals that are linked by disulfides. The combination of IL-6 and TGF-β1 in conjunction with IL-23 induce Signal Transducer and Activator of Transcription-3(STAT-3) and Retinoid-related Orphan Receptor gammat(RORγt) of T help 17 to release IL-17. The combination of IL-17 and IL-17 Receptor A can stimulate the local release of TNF-α,IL-1β,IL-6,IL-8,acute-phase protein,granulocyte-macrophage colony-stimulating factor(GM-CSF) and macrophage inflammatory protein-2 (MIP-2). The interactions among those cells further enhance the secretion of many more inflammatory cytokines. Consequently, all those inflammatory cells as well as their cytokines constitute a complex network to promote inflammatory diffusion. Due to the lack of expression and detailed mechanisms of related cytokines of Th17/IL-17 such as IL-17,IL-17RA,IL-23,TNF-αand IL-1βin severe pneumonia, this study was designed to investigate the expression of related cytokines of Th17/IL-17 in rat severe pneumonia by induced Klebsiella pneumoniae and to explore their roles in the pathogenesis of severe pneumonia.Objective:To investigate the expression and significances of relate cytokines of Th17/IL-17 such as IL-17,IL-17RA,IL-23,TNF-αand IL-1βin rat severe pneumonia by induced Klebsiella pneumoniae.Methods:1. The rat model of severe pneumonia was established by intratracheally injected Klebsiella pneumoniae.2. Rats were divided into pneumonia model group(n=36) and control group (n=36).Each group were divided into six subgroups(the subgroups of 4hour,12hour,1day,3day,5day,7day). The leukocytes and neutrophils in the BALF and peripheral blood were detected, arterial blood gas analysis was measured from abdominal aorta, the colonies in rat lung homogenates were counted, histopathology of lung was carried out. 3. The protein concentration of IL-23,IL-17,IL-1βand TNF-αin the BALF were detected by ELISA. Total RNA was isolated from the lung and mRNA expression of IL-17,IL-17 RA,IL-1βand TNF-αat the set time were assayed by Fluorescent real-time quantitative PCR.Results:1. It was found that Model group rats had obvious poisoning infection symptoms such as shortness of breath, obvious cyanosis, portion of sleepiness, significant reduction in urine output. It was found that bilateral multi-leaf lesions in lung tissue by both gross and microscopic pathology, leukocytes and neutrophils increased significantly in peripheral blood, arterial partial pressure of oxygen declined progressively. The results all above are the most serious at 5 days after rats challenged by Klebsiella bacterial.2. The mRNA levels and protein concentration of IL-17,IL-17RA and IL-23 were detectable at 4h and peaked at 3 days after challenged by Klebsiella pneumonia.IL-1βand TNF-αmRNA levels and protein concentration peaked at 5th day after bacterial challenge, no later than the expression of IL-17 and IL-17RA,IL-23.3. The count of neutrophils in BALF was detectable 4 hour and peaked at 3 day after challenged by Klebsiella pneumonia compared with control group. The concentration of IL-23 and IL-17 were positively correlated with the counts of neutrophils in BALF(r=0.72,P<0.01;r=0.79,P<0.01).Conclusions:1. Intratracheal instillation of Klebsiella pneumoniae can successfully establish the rat model of severe pneumonia.2. Compare with IL-1βand TNF-α,IL-17,IL-17RA and IL-23 are more earlier pro-inflammatory factor in Klebsiella pneumonia.3. The IL-23/IL-17 axis augments neutrophils recruitment to the respiratory tract, thus promotes the occurrence and development of inflammation.