Local activation of the complement system in endoneurial microvessels of diabetic neuropathy

Quantitative immunocytochemical analysis of complement proteins (CP) was pe rformed on sural nerve biopsies from 15 patients with diabetic neuropathy ( DN) and Is nondiabetic patients with other forms of chronic neuropathy (ON) . The mean age of the patients and the pathological severity of the neuropa thy were similar in both groups. The percentage of patients that expressed strongly immunoreactive CP in the walls of endoneurial microvessels was sig nificantly greater in DN than in ON for all proteins tested. C3d neoantigen was expressed in 100% of DN cases compared with 17% of ON; and membrane at tack complex (MAC), C5b-9 neoantigen, in 93% of DN and 17% of ON. In the ca ses with DN, 81% of endoneurial microvessels, as identified by the endothel ial marker, Ulex europaeus, contained C5b-9 neoantigen deposits, compared w ith 22% in those of ON, and the staining in DN was significantly more inten se. Expression of the neoantigens of C3d and C5b-9 in nerve implies local a ctivation of the complement system. In DN, activation of the complement pat hway and formation of the MAC could injure blood vessels and adversely affe ct the circulation in the endoneurium.