Systemic SP-A is increased in COVID-19 patients with abnormal diffusion capacity 6 months after hospital discharge

Introduction: Recent studies show reduced carbon monoxide lung diffusion capacity (DLCO) after hospital discharge in patients with COVID-19 pneumonia. Underlying mechanisms are unknown. We hypothesize that innate immunity mediators secreted by lung type II epithelial cells (AEC-II) and Club cells involved in lung homeostasis and resolution of inflammation may play a role. Aim: To determine systemic surfactant protein A (SP-A), SP-D and club cell secretory protein-16 (CC16) levels in COVID-19 patients at 6 months after hospital discharge and their relationship with DLCO. Methods: We collected plasma samples from 85 patients discharged from Clinic Barcelona because of COVID-19 pneumonia. All patients followed the current SEPAR consensus for post-COVID-19 follow-up. DLCO was measured following international recommendations. Systemic SP-A, SP-D and CC16 levels were measured by ELISA. Results: Mean age of patients was 50±25, 35 of them were males (41%) and 5 were current (6%) and 18 former (21%) smokers. Hypertension was common (33%) and 28% of patients required ICU hospitalization. DLCO was <80% of predicted value in 33 patients (39%). Circulating SP-A levels were increased in patients with low DLCO (2358±309 vs 1432±220 pg/ml, p=0.006) compared with high DLCO. No significant differences were observed in SP-D (165±16 vs 143±10 ng/ml, p=0.5) or CC16 (36.7±3 vs 36.5±2 ng/ml, p=0.9) levels. Conclusions: Circulating SP-A levels are increased in COVID-19 patients with abnormal DLCO 6 months after hospital discharge, suggesting persistent pro-inflammatory AEC-II cells phenotype in these patients. Supported by Fundació Glòria Soler, Fundació BBVA, FCRB and HCB-IDIBAPS-COVIDBANK.