This project's objective is to identify the autoantigen in cholinergic neurons that is the target of pathogenic antibodies in the Lambert-Eaton myasthenic syndrome (LES). The long-range goal is to devise antigen-specific therapy for LES. Striking features of LES include a greater than 55% incidence of a lethal lung cancer, small cell (oat cell) carcinoma (SCC), and a high prevelence of autoantibodies to thyroid and stomach constituents. Weakness results from a deficient exocytosis of acethylcholine (ACh) from motor nerve terminals in response to a nerve impulse. Injection of IgG from serum of patients into mice causes a neurotransmission defect similar to that of LES. There is considerable evidence that the abnormality of cholinergic neurons that impairs neurotransmission in LES results from an autoimmune response that is initiated as an anti-tumor response directed against a neuron-related differentiation antigen of SCC. Voltage-sensitive Ca2+ channels have been implicated as the antigen. This project aims to examine plasma membranes of SCC for antigens reactive with LES antibodies and for molecules related to those on cholinergic neurones that are relevant to ACh release. LES patients' antibodies will be tested for pathophysiologic effects on clonal lines and primary preparations of cholinergic neurons, using microassays to measure voltage-dependent influx of 45Ca2+ and release of 3H-ACh. A new rapid passive transfer model of LES in mice will facilitate analysis of the mechanisms responsible for impaired release of ACh quanta in LES. Isolated cholinergic nerve terminals from the electric organ of Torpedo californica will be investigated as a potentially rich source of the LES antigen. The omega toxin of the snail Conus geographus, which has high affinity and specificty for voltage-sensitive Ca2+ channels of presynaptic nerve terminals, is a promising tool for identifying the LES antigen. Monoclonal antibodies made by hybridomas from rats immunized with SCC or cholinergic neuronal components, and by B cell lines from LES patients, will be used to identify and purify the LES antigen.
The aims i n the next period of this grant are 1) to identify and purify the LES antigen, 2) to develop an animal model of LES based on active immunization for testing new modes of therapy for LES; 3) to develop serologic tests for diagnosis of LES and/or SCC; and 4) to identify the Link between SCC, LES and thyrogastric autoimmunity.
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