Characterization of an antiserum against an axolemma-enriched fraction

Antibodies to the axolemma-enriched fraction in the cerebrospinal fluid and serum of patients with multiple sclerosis and other neurological diseases

Antibodies to an axolemma-enriched fraction (AEF) antigen have been detected in the cerebrospinal fluid (CSF) and serum of patients with Multiple Sclerosis (MS) using an enzyme-linked immunosorbent assay (ELISA). A marginal elevation (P < 0.08) of anti-AEF IgG was found in MS CSF when compared with OND samples. When CSF was diluted to a standardized IgG concentration, the anti-AEF IgG level in MS CSF was significantly elevated (P=0.007) when compared to OND CSF. MS serum was also found to contain a significantly higher level (P < 0.001) of anti-AEF IgG when compared to OND serum using the ELISA technique.

Functional evidence for the role of axolemma in CNS myelination

A direct role for neurons in CNS myelination has yet to be demonstrated. CNS myelination can be examined in cerebellar slice cultures, which faithfully reproduce both synthesis and wrapping of myelin. In an attempt to demonstrate a role for axolemma in this process, we generated more than 2000 axolemma-reactive monoclonal antibodies. One clone, G21.3, repeatedly blocked myelination in cerebellar slices, as documented by both biochemistry and morphology. The antibody caused a dramatic reduction in myelin lipid and protein synthesis. CNS white matter, sciatic nerve, and neuronal cultures were positively stained with G21.3, whereas oligodendrocytes and myelin were fully negative. The antibody identified a restricted number of proteins in purified axolemma. These results suggest a direct involvement of axons in CNS myelination.

Antisera to the ganglioside GM1 do not have anti-myelin or anti-axon activities in vitro

Four antisera to the ganglioside GM1 were tested for effects on myelin and axons when applied to mouse spinal cord-dorsal root ganglia explant cultures. None of the antisera to GM1 caused myelination inhibition or demyelination, while an antiserum to galactocerebroside caused both. Antisera to GM1 did not inhibit axonal outgrowth or destroy mature outgrowth zone axons, while an antiserum to a rat brain axolemma-enriched fraction did both. These results suggest that antibodies to GM1 do not have significant anti-myelin or anti-axon activity.

Antisera to an axolemma-enriched fraction inhibit neurite outgrowth and destroy axons in vitro

Antisera prepared to an axolemma-enriched fraction derived from rat brain inhibited neurite outgrowth and destroyed mature axons in spinal cord-dorsal root ganglia cultures. Similar antibody-mediated anti-axon effects may be important in some diseases of the human nervous system.

Differential proliferative responses of cultured Schwann cells to axolemma and myelin-enriched fractions. II. Morphological studies

Axolemma-enriched and myelin-enriched fractions were prepared from bovine CNS white matter and conjugated to fluorescein isothiocyanate (FITC). Both unlabelled and FITC-labelled axolemma and myelin were mitogenic for cultured rat Schwann cells. Treatment of Schwann cells with the FITC-labelled mitogens for up to 24 h resulted in two distinct morphological appearances. FITC-myelin-treated cells were filled with numerous round, fluorescent-labelled intracellular vesicles, while FITC-axolemma-treated cells appeared to be coated with a patchy, ill-defined fluorescence, primarily concentrated around the cell body but extending onto the cell processes. These observations were corroborated under phase microscopy. Electron microscopy revealed multiple, membrane-bound, membrane-containing phagosomes within myelin-treated cells and to a far lesser extent in axolemma-treated cells. The effect on the expression of the myelin-mediated and axolemma-mediated mitogenic signal when Schwann cells were treated with the lysosomal inhibitors, ammonium chloride and chloroquine, was evaluated. The mitogenicity of myelin was reduced 70-80% by these agents whereas the mitogenicity of axolemma was not significantly altered under these conditions. These results suggest that axolemma and myelin stimulate the proliferation of cultured Schwann cells by different mechanisms. Myelin requires endocytosis and lysosomal processing for expression of its mitogenic signal; in contrast, the mitogenicity of axolemma may be transduced at the Schwann cell surface.