Blood-nerve barrier studies in experimental allergic neuritis

The integrity of the blood-nerve barrier (BNB) was studied during the development of experimental allergic neuritis (EAN). Lewis rats immunized with bovine nerve or myelin plus complete Freund's adjuvant developed histological lesions of EAN in nerve roots by 10-12 days and in sciatic nerves by 12-14 days. Evans blue-albumin (EBA) and horseradish peroxidase (HRP) were injected i.v. 1 h prior to killing on days 6-18. Perivascular and diffuse endoneurial leakage of the tracers was seen in nerve roots by 10-12 days post immunization (p.i.) and in sciatic nerves by 12-14 days. This coincided with the appearance of endoneurial infiltration with inflammatory cells and endoneurial proteinaceous edema at a time when Schwann cell and myelin changes were still minimal. Therefore, an alteration in BNB permeability occurs early in EAN, coincident with inflammatory cell infiltration. This could be an expression of delayed hypersensitivity, yet it would also facilitate the entry of anti-myelin antibodies into the endoneurium where they could initiate demyelination.