Immunohistochemical findings in vasculitic neuropathies.

Fifteen sural nerve biopsies of vasculitic neuropathies have been compared with 11 cases of different non-vasculitic neuropathies and normal nerves from brain-dead organ donors. The APAAP (alkaline phosphatase monoclonal anti-alkaline phosphatase) immunostaining method was applied to cryostat sections from unfixed snap-frozen tissue samples. Immunoglobulins IgG, IgM, IgA, complement factors and light chains were reactive in biopsies of normal nerves as well as of vasculitic and nonvasculitic neuropathies. A strong reaction against IgE in the epineurial vessel walls was only seen in cases of Churg-Strauss-vasculitis. Antibodies against MHC class II (HLA DR) were positive in most of vasculitic infiltrates. Vascular endothelial cells were positive with anti MHC class I in all biopsies. A typical finding in all vasculitic neuropathies was the infiltration of epineurial vessels with CD4 positive and, to a lesser extent, CD8 positive lymphocytes. CD22 positive lymphocytes (B cells) have only been seen in about one third of vasculitic neuropathies. CD16 positive cells (NK-cells or neutrophils) could be demonstrated only in two biopsies. CD68 positive cells (macrophages) are frequently seen in most cases of neuropathy regardless of their etiology. The results support the concept of a primary T-cell mediated process against epineurial vessels as the most important mechanism in the pathogenesis of vasculitic neuropathies. In some cases with small epineurial infiltrates the vasculitic process can only be recognized with antibodies against CD4 or CD8. Therefore, the immunohistochemical evaluation of sural nerve biopsies may be helpful for identifying cases with microvasculitis.