Background and aims Interstitial lung disease (ILD) is common in systemic lupus erythematosus (SLE) patients. These patients tend to have large amounts of autoantibodies. Blood memory Tfh17 cells represent efficient B cell helper cells with distinct capacities to induce IgG and IgA secretion and to regulate immunoglobulin isotope switching. Recent study found overall Tfh17 cells are highly presented in peripheral blood of SLE patients. However, it is not clear how different subsets of Tfh17 cell are distributed in broncholalveolar lavage fluid (BAL) and peripheral blood of SLE-ILD patients. The study is to determine the proportion of different Tfh17 cell subsets (activated Tfh17: CXCR3-CCR6+ICOS+PD-1++CCR7lo, quiescent: CXCR3-CCR6+ICOS-PD-1+CCR7int and CXCR3-CCR6+ICOS-PD-1-CCR7hi) among CD4+ T cells and levels of immunoglobulins in BAL and peripheral blood of SLE-ILD patients.

Methods 30 SLE-ILD patients were included. The lung disease were proved by high resolution CT scan. Patients underwent bronchoscopy and BAL were collected. Tfh17 cell profiles were determined using flow cytometry. Levels of immunoglobulins were detected by ELISA. Statistics were analysed by SPSS 22.0.

Results IgA and IgG levels were significantly higher in BAL than in blood. Activated Tfh17 in BAL was increased significantly (p=0.011) and both subsets of quiescent Tfh17 cells were decreased (p<0.05) compared to those in the blood. The activated Tfh17 was positively correlated with IgA level (r=0.871, p=0.039) in BAL and with IgG level (r=0.714, p=0.047) in blood.

Conclusions Activated Tfh17 is more abundant in BAL than in blood and switches from IgG correlation to IgA correlation, suggesting its role in the pathogenesis of SLE-ILD.