Expression of Thy-1 antigen in reactive endoneurial capillaries of the rat following peripheral nerve damage

Immunohistochemical staining of Thy-1 antigen was studied in rat peripheral nerves shortly after a complete crush lesion and after an epineural depot injection of lysophosphatidylcholine-palmitate (lysoPC). The Thy-1 antigen was expressed in endoneurial capillaries after 20-30 h and was visible previous to alterations in the axolemma or other signs of neural damage with the exception of endoneurial oedema formation. Thy-1 positive capillaries were restricted to the vicinity of degenerating nerve fibres in partially damaged nerves following epineural depot injection of lysoPC. It is therefore concluded that expression of the Thy-1 antigen in response to peripheral nerve damage in reactive endoneurial capillaries is an active process and not due to diffusion from degenerating axolemmata. Thy-1 staining could be used as a marker of reactive endoneurial capillaries in pathological conditions of peripheral nerves.