Acetylcholine receptor (AChR) antibodies are autoantibodies produced by the immune system that mistakenly target proteins called acetylcholine receptors that are located on muscles that you can consciously or voluntarily control (known as skeletal muscle fibers). This test detects and measures AChR antibodies in the blood.
Muscle movement starts when an impulse is sent down a nerve to the nerve ending, where it stimulates the release of acetylcholine, a chemical substance (neurotransmitter) that transmits messages between specific types of cells. Acetylcholine travels across the very small gap between the nerve ending and a muscle fiber (this gap is called the "neuromuscular junction").
When acetylcholine reaches the muscle fiber, it binds to one of many acetylcholine receptors or "docking stations" and activates it, initiating muscle contraction.
AChR antibodies impede communication between nerves and skeletal muscles, inhibit muscle contraction, and cause rapid muscle fatigue by preventing activation of the acetylcholine receptors. They do this in three major ways:
- Binding antibodies attach to the receptors on nerve cells and may initiate an inflammatory reaction that destroys the receptors.
- Blocking antibodies may sit on the receptors, preventing acetylcholine from binding.
- Modulating antibodies may cross-link the receptors, causing them to be taken up into the muscle cell and removed from the neuromuscular junction.
The end result of this interference is the development of myasthenia gravis (MG), a chronic autoimmune disorder associated with the presence of these antibodies and with their effects on muscle control.
AChR antibodies may be detected in different ways to determine which mechanism may be the problem, and the antibodies may be referred to as "binding," "blocking," or "modulating." However, the technique that measures "binding" is the most commonly performed and, generally speaking, it is rare for the other two tests to be positive without the "binding" test being positive as well. These other two tests may be useful when a healthcare practitioner strongly suspects myasthenia gravis and the "binding" test is negative.
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A negative test result does not rule out MG. Up to 50% of those with ocular MG (affecting only eye-related muscles) and about 10-15% of those with generalized MG will be negative for AChR antibodies. Repeat testing of AChR antibodies in those with initially negative results may be useful as the concentration of antibodies may increase as the disease progresses, resulting in a subsequent positive AChR antibody test result.
Acetylcholine Receptor Ganglionic (Alpha 3) AB
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