Alzheimer's disease antibodies bind specifically to a neurofilament protein in Torpedo cholinergic neurons

Alzheimer's disease (AD) is characterized by neurofibrillary tangles and neuritic plaques and by the degeneration of central cholinergic neurons. Recent studies indicated the presence of antibodies in the sera and cerebrospinal fluid of AD patients which react with neuronal tissue and which recognize cholinergic neurons. In order to identify the cholinergic antigens against which the AD antibodies are directed, we have recently used the purely cholinergic electromotor neurons of the electric fish Torpedo which are chemically homogenous and cross-react antigenically with mammalian cholinergic neurons. This study revealed that immunoglobulins (IgG) from sera of AD patients bind specifically to an antigen in Torpedo electromotor neurons with an apparent molecular weight of 200 kDa. In the present report we attempt to characterize this antigen. The similarity in size of this protein to that of the heavy neurofilament subunit (NF-H) and the association of neurofilaments with plaques and tangles prompted us to examine the possibility that it is a neurofilament protein. Our findings show that IgG from sera of AD patients bind to the NF-H protein of Torpedo cholinergic neurons. Comparison of the binding of AD and control IgG to Torpedo cholinergic NF-H revealed that AD IgG bind to this neurofilament protein more readily than do control IgG. In contrast, AD and control IgG bind similarly to NF-H obtained from the chemically heterogenous Torpedo spinal cord and rat brain. These findings suggest that AD sera contain a repertoire of anti-NF-H IgG and that a subpopulation of these antibodies whose levels are significantly elevated in AD binds to epitopes highly enriched in Torpedo cholinergic NF-H.(ABSTRACT TRUNCATED AT 250 WORDS)