Additional profiling of immune response-related genes highlighted the preferential proximal PAS usage of immunoglobulin genes, such as IGHM, IGHG1, IGHG3, and IGHA2, especially in B cells and plasma cells of COVID-19 samples (Fig. 5h; Additional file 1: Fig. S10C). The gene discussed is IGHG1; the disease is COVID-19.