Immunocytochemical staining for glial fibrillary acidic protein and the metabolism of cytoskeletal proteins in experimental allergic encephalomyelitis.

Spinal cord sections from Lewis rats with acute experimental allergic encephalomyelitis (EAE) showed greatly increased staining of astrocytes when stained immunocytochemically for glial fibrillary acidic protein (GFAP). Fibrous processes in white matter were heavily stained early in the course of the disease when paralysis was first evident (10-12 days after injection of guinea pig spinal cord myelin), then protoplasmic astrocytes were stained in the gray matter and became more heavily stained at 20 days post-injection. The stained astrocytes were evenly distributed throughout the tissue, and did not correspond to the sites of the lesions. Spinal cord slices of control and EAE rats were incubated with [3H]amino acids, then cytoskeletal proteins were prepared in an enriched fraction, separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and the protein bands counted for radioactivity. In the EAE rat all cytoskeletal proteins, including the neurofilaments, vimentin, microtubules, GFAP and actin, showed increased uptake of radioactive amino acids. Immunoprecipitation of GFAP with specific antiserum showed increased radioactivity in the complex beginning at day 10 when cellular infiltration was beginning in the EAE animals. As the disease became acute, the radioactivity in the immunoprecipitated GFAP increased, in some cases to very high levels, then by day 18 when recovery was underway, the radioactivity had fallen to normal levels. Possible agents causing metabolic activation of protein synthesis in EAE animals include stimulating substances elaborated by infiltrating lymphoid cells, and the generalized edema accompanying the demyelinative condition. The activation of GFAP protein staining and metabolism in EAE might serve as a model for the activated growth of astrocyte processes which cause the severe gliosis seen in multiple sclerosis.