The muscarinic cholinergic receptor 4 (M4)-EIA is an antibody screening test. M4 receptor has been pre-coated onto a microtiter plate. During the first incubation the anti-muscarinic cholinergic receptor 4 antibodies of the samples are immobilised on the plate. The autoantibodies are detected with a POD labeled anti-human IgG antibody. In the following enzymatic substrate reaction the intensity of the colour correlates with the concentration and/ or avidity of anti-muscarinic cholinergic receptor 4-antibody. Sample Types: serum. Range: 2.5 - 40 U/ml. Sensitivity: Cut-off. Time: 3.5 hours ? Muscarinic cholinergic receptors, or mAChRs, areacetylcholine receptors that form G protein-receptorcomplexes in the cell membranes of certain neuronsand other cells. Autoantibodies against M4 AChR aresignificantly elevated in patients suffering fromchronic fatigue syndrome (CFS) / myalgicencephalomyelitis (ME). Muscarinic cholinergicreceptor 4 (M4) autoantibodies are present in asubset of 20-30% of chronic fatigue syndromepatients.The Eagle Biosciences anti-muscarinic cholinergic receptor 4(M4)-Antibody EIA is designed for the determinationof antibodies against the muscarinic cholinergicreceptor 4 (M4) in serum.