Uptake of antineuronal IgM by CNS neurons: comparison with antineuronal IgG

We examined the axonal transport of monoclonal IgM that binds to Thy 1.1, a glycoprotein component of the neuronal and synaptic plasma membrane, in the rat, using immunohistochemical techniques. IgM immunoreactivity appeared in neurons 1 to 2 days following injection in their terminal fields. Several neural pathways supported retrograde axonal transport of IgM, including facial nucleus, hypoglossal nucleus, and thalamic projections. Although the IgM studied had a greater affinity for Thy 1.1 than the IgG, IgM axonal transport was more difficult to detect than axonal transport of IgG, suggesting that IgM undergoes retrograde axonal transport less readily than IgG. An increase in intraneuronal IgM may serve as an index of the action of antineuronal IgM at the presynaptic membrane, and intraneuronal IgM may be directly involved in the pathogenesis of some types of motor neuron disease and neuropathy.