Significance Of Serum KL-6 Detection In Connective Tissue Disease Complicated Associated Interstitial Lung Disease

BackgroundConnective Tissue Disease（CTD）is a group of chronic,nonspecific,inflammatory,and immune diseases that affect blood vessels,skin,bones,joints,and muscles throughout the body,including Rheumatoid Arthritis（RA）,Systemic Lupus Erythematosus（SLE）,Systemic Sclerosis（SSC）,Polymyositis（PM）/Dermatomyositis（DM）,Sjogren’s syndrome（SS）,Mixed Connective Tissue Disease（MCTD）and vasculitis,etc.,which can involve all organs of the body and easily affect the lungs.The main lesion is interstitial lung disease（ILD）,a group of heterogeneous and diffuse interstitial diseases,which is one of the main causes of poor prognosis and death in patients with CTD^[1].At present,the diagnosis of connective tissue disease associated interstitial lung disease（CTD-ILD）mainly depends on the patient’s symptoms,signs,chest high-resolution CT（HRCT）,lung function measurement,lung biopsy,etc.However,these methods have disadvantages such as poor reproducibility and trauma,and are easy to miss diagnosis and misdiagnosis.On the other hand,they are not conducive to follow-up and monitoring.Type Ⅱ alveolar epithelial cell secretion of large molecules（200 kda）antigen of sialic acid sugar chain KL-6（Krebs Von den Lungen-6）,is a marker of alveolar epithelial cell injury and regeneration by immunohistochemical results^[2],is the combination of connective tissue disease associated interstitial lung disease（CTD-ILD）one of the most studied serum marker,studies have shown that compared to patients with ILD,ILD in patients with significantly increased serum levels of KL-6^[3],There was no significant difference in plasma KL-6 concentration between SSC-ILD group and SSC-NILD group^[4].Most of the relevant studies confirmed the value of KL-6 in the diagnosis of CTD-ILD,and most of its diagnostic threshold fluctuated around 500U/ml.There is still a lack of systematic standard for the treatment of CTD-ILD,mainly through the evaluation of the overall condition of the patient,to determine the treatment program,the current treatment program selection of individual differences;The main drugs include hormone and immunosuppression,as well as anti-fibrosis therapy,but the efficacy is not clear yet.Meanwhile,there is a lack of relevant studies on the evaluation of the efficacy of KL-6 drug therapy.PurposeBy detecting the serum KL-6 concentration of patients in the CTD control group and the CTD-ILD experimental group,compares the difference between two groups,and analyzes the CTD patients serum concentrations of KL-6-ILD group and other blood tests index:white blood cell count（WBC）,neutrophil percentage（NEU%）,C-reactive protein（CRP）and blood sedimentation（ESR）,further validation of serum KL-6 in CTD-ILD value in the diagnosis and assessment of his condition;The level of serum KL-6 and its relationship with the area of chest HRCT lesions in the CTD-ILD group before and after treatment were detected to evaluate the value of serum KL-6 in the evaluation of treatment reactivity.MethodsA total of 45 patients with newly diagnosed CTD-ILD in the Department of Rheumatology and Immunology of our hospital from January 2019 to December 2020were collected,and 30 patients with newly diagnosed matched CTD without ILD were collected during the same period.Basic information and data of all enrolled patients,such as age,sex,disease type and laboratory indicators,radiographic examination（chest HRCT）results,were recorded.The concentration of serum KL-6 was detected by chemiluminase immunoassay,and SPSS 25.0 statistical software was used for statistical analysis and correlation analysis.ResultsA total of 75 patients were included in this study,including 45 patients with CTD-ILD,30 patients with CTD-NILD,and 18 patients in the CTD-ILD treatment group.The average serum KL-6 concentration of CTD-ILD group was 536.0（447.0,706.0）U/m L,which was significantly higher than that of CTD-ILD group(201.0（142.5,289.0）U/m L,and there was significant difference between groups（P<0.05）.The optimal critical value of KL-6 in the diagnosis of secondary ILD in CTD patients was 377.0 U/m L by ROC curve analysis.There was no correlation between KL-6 concentration and CRP,WBC,N%laboratory indexes,and there was a positive correlation with ESR.The correlation coefficient between chest HRCT lesion area and serum KL-6 concentration in CTD-ILD group before and after treatment was 0.978 and 0.758 respectively,showing a positive correlation,and the average concentration of KL-6 after treatment was 661.56±243.19 U/m L.It was significantly lower than that of the group before CTD-ILD treatment（828.89±310.02 U/m L）,and there was a significant difference between the control groups（P<0.05）.Conclusion1.Serum KL-6 is an important serological marker for the diagnosis and monitoring of the disease activity of CTD-ILD.2.Serum KL-6 can be used as a serological marker to evaluate the therapeutic effect of CTD-ILD.