Immunocytochemical studies of serum proteins and immunoglobulins in human sural nerve biopsies.

Post-embedding immunocytochemical studies on immunoglobulins (Ig) and other serum proteins were carried out on 38 human sural nerve biopsies using the PAP method. In addition to toxic, hereditary, metabolic, dysproteinemic, and vasculitic-neuritic neuropathies, morphologically normal sural nerves were included as controls. The intensity of the immunocytochemical reactions was strong for proteins, such as IgG, the light chains of Igs, and albumin, but weak or absent for others like complement component C3, IgA, ceruloplasmin, and alpha-1-antitrypsin (AAT) in normal nerve biopsies and in all pathologic groups. IgG, the light chains of immunoglobulins, and albumin could readily be detected in perineurium, endoneurial interstitium, and blood vessel walls. IgM, C3, and beta-lipoprotein (BLP) were largely confined to the walls of blood vessels and perineurium, thus indicating that they do not penetrate the blood nerve barrier. Only in a few cases, in vasculitic-neuritic and dysproteinemic neuropathies, staining of the endoneurial interstitium for IgM and C3 was observed. Increased staining for the corresponding heavy or light chains was not detected in the endoneurium in any of the neuropathies associated with gammopathy. The results stress that PAP immunocytochemistry is suitable for studying the blood-nerve barrier (BNB) and provides new aspects to the concept of the BNB with respect to the steady state of serum proteins between endoneurial and vascular spaces. It is suggested that, in addition to serum concentration and molecular weight of serum proteins, the permeability of the BNB is influenced by other yet undefined factors.