Footnotes

• Handling editor Iskander Chaudhry.

• Contributors All the authors contribute to the conception of the work, the immunohistochemical analysis and its interpretation, the acquisition of the pictures, and the drafting the work.

• 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.