The Levels Of Toll-like Receptor 7 Gene MRNA In The Lung Of Asthmatic Rats

In recent decades, the morbidity of asthma is one of the dramatically increased diseases among the pediatric respiratory tract diseases. More and more related factors of asthma were found as many research on asthma performed. Hence, we now can further understand the pathogenesis, progression and therapy of asthma. However, up to now, the exact pathogenesis of asthma is still unclear and can not cure asthma.Human Toll-like receptors (TLRs), a family member of transmembrane receptor for signal transduction, are discovered in recent years. They can identify and combine with pathogen-associated molecular pattern, then trigger a series of signal transduction, and lead to release of inflammatory mediators. They play an important role in the innate immune defenses, and lead antigen-presenting cells (APCs) to recognize pathogens and release stimulus signal to start of acquired immune response. Hence, TLRs are a bridge of human innate and acquired immunity. TLR7, an important member of the TLRs family, plays an important role in both physiology and pathology. It is very important for our body to maintain the normal function of TLRs. Reduce or enhance the function of TLRs would harm to the body and cause some disorders. For example, M(?)ller-Larsen S. et al. studied about the function of TLR7 and TLR8, and found TLR7 and TLR8 has an important role in the mechanism in asthma. Du Q. et al. found that Imiquimod (a kind of ligand of TLR7) can inhibit remodeling of respiratory tract in asthma model of rats. Camateros P. et al. found that S28463 (ligand of TLR7/8) prevent airway remodeling caused by chronic asthma. Moisan J. et al. found ligand of TLR7 can prevent hyperresponsiveness of airway and eosinophilia caused by allergen, that is to say,the activity of TLR7 can treat asthma. Roponen M et al. studied the levels of expression of myxovirus resistancd protein A and 2'5'-oligoadenylate synthetase mRNA of interferon-gamma inducible cytokine protein 10 (IP-10) and IL-6 protein synthesis. They found that the three indicators were lower in asthma patient than in healthy one after activating TLR7, and that the serum IgE and IP-10 had a negative relationship, all of this results were only found after activating of TLR7, but not TLR3, which indicated that the function of TLR7 was lower in asthma patient than in healthy one. However, Roponen M only studied the three indicators. We now know, TLR7 can transmit message into the cell by TIR after being activated, then causes a serious of reaction, activate the nuclear factor NF-κB. Then, the cell secrete many inflammatory factors, such as IL-1, IL-6, IL-12 and TNF-α. All of this factors have not be measured by the scholars. That is to say, TLR7 has close relations with asthma, but it is still unclear about acute role of TLR7 in physiology and asthma.ObjectiveWe established a rat asthmatic model by ovalbumin (OVA) sensitized. The aim of this study is to investigate the effect of TLR7 on asthma and the mechanisim of Dexamethasone (Dex) on asthmatic intervention by measuring the expression of TLR7 and NF-κB mRNA in the lung of asthmatic group, Dex intervention group and control group.Methods1. Asthmatic model and groupsA total of 27 Wister rats were randomly divided into 3 groups.Asthmatic group: Sensitized intraperitoneally and challenged intranasally by OVA, then intragastric administration with a dose of 5 ml/kg normal saline one time everyday for 5 days.Intervention group: Sensitized intraperitoneally and challenged intranasally by OVA and intragastric administration with a dose of 5 mg/kg Dex one time everyday for 5 days.Control group: Intraperitoneal, intranasal and intragastric administration with normal saline. The methods and duration were same with other 2 groups.After the last intragastric administration, 2% sodium pentobarbital anesthesia was injected intraperitoneally and the rats were killed, then the specimens were collected for real time PCR and pathology detection.2. Real time PCRReal time PCR was used to detect the mRNA levels of TLR7. TRizol was used to extract total RNA from lung tissues, then, be reverse transcriptased and amplified with SYBR Green Kit (Takara Company).3. Pathological examinationThe tissue were fixed with neutral formalin, dehydration, xylene transparent, paraffin-embedd, sections, and finally stained with HE and Giemsa staining for pathological observation.Results1. Shortness of breath and other asthmatic sympatoms were noeted in asthma group. Airway wall thickening, increased secretions and eosinophil infiltration were noted in the lung of asthmatic group. These findings were consistent with the characteristics of asthma.2. The levels of TLR7 mRNA in lung tissue of asthmatic group was higher than that of the control group with a significant difference (P < 0.001). The levels of TLR7 mRNA in the lung of Dex intervention group were lower than that of asthmatic group (P = 0.004), but still higher than that of the control group (P < 0.001).3. The levels of NF-κB mRNA in lung tissue of asthmatic group was higher than that of the control group with a significant difference (P = 0.001). The levels of NF-κB mRNA in the lung of Dex intervention group were lower than that of asthmatic group (P = 0.006), but still higher than that of the control group (P = 0.008).Conclusions1. The TLR7 mRNA levels in the asthmatic rats higher than that of the controls, which suggests that TLR7 may be one of the mechanisms of asthma.2. The decreased TLR7 mRNA levels after Dex treatment suggests that corticosteroids may play a role in its anti-inflammatory through the restoration of TLR7 gene expression.3. The similar tendency of NF-κB and TLR7 suggests that NF-κB maybe mediate the role of TLR7 in asthma.