Abstract: Objective To observe the level of monocyte/macrophage subsets in patients with connective tissue diseases associated interstitial lung disease (CTD-ILD). Methods A total of 77 CTD patients hospitalized at department of respiratory and critical care medicine in Characteristic Medical Center of Chinese People's Armed Police Force from July 2017 to February 2018 were recruited. The patients were divided into the CTD-ILD group (n=47) and the CTD-nILD group(n=30) according to whether CTD combined with ILD. The general information, pulmonary function tests and HRCT data were collected in the two groups of patients. (1) Thirty cases with normal physical examination were recruited as healthy control group (NC group). The circulating monocytes subtypes were measured by flow cytometry. (2) Twenty-five patients in the CTD-ILD group who underwent bronchoscopy were selected as experimental group, and 20 patients (include cough and chest tightness) with normal chest imaging and bronchoscopy results were enrolled as control group. Macrophage subtypes of bronchoalveolar lavage fluid (BALF) were measured by flow cytometry. Results 1. The Mon2 circulating monocytes were significantly higher in the CTD-ILD group (6.32±2.60) than those in the CTD-nILD group (5.00±1.52) and NC group (3.65±1.36, P＜0.05). The proportion of Mon2 circulating monocytes was positively correlated with gross glass score (r=0.372, P= 0.010). 2. The proportion of M2 macrophage was significantly higher in CTD-ILD group than that of control group (t=-6.520,P＜0.001). Conclusion In the patients of CTD-ILD, the levels of Mon2 monocytes and M2 macrophages increase significantly, which might be closely related with the development of ILD.

Key words: connective tissue disease, interstitial lung disease, monocyte, macrophage, flow cytometry