1. Division of Respiratory Medicine, Mito Medical Center, University of Tsukuba, Ibaraki 310‑0015, Japan
2. Faculty of Medicine, Mito Medical Center, University of Tsukuba, Ibaraki 310‑0015, Japan
3. Division of Pathology, Mito Medical Center, University of Tsukuba, Ibaraki 310‑0015, Japan