Footnotes

• Handling editor Josef S Smolen

• Contributors M-KT drafted the manuscript. Y-LC performed the pathological analysis. C-CL critically reviewed the manuscript. H-CC, F-CL and D-MC conceptualised the study. All authors reviewed the manuscript.

• Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

• Competing interests None declared.

• Provenance and peer review Not commissioned; externally peer reviewed.