Tissue transglutaminase antibodies

In 1997, Dieterich et al. [6] identified tissue transglutaminase (tTG) as the autoantigen for EMA. tTG is a calcium-dependent enzyme which catalyses crosslink formation between glutamine residues and lysine residues and is expressed in many organs and stored mainly intracellularly. It is possible to detect autoantibodies to tTG by ELISA [7]. Wells are coated with calcium-activated guinea pig liver tTG. Serum, diluted to one in 100, is added and incubated for an hour. Peroxidase-

conjugated antihuman IgA or IgG is added, and, after incubation with substrate, the absorbance is read spectrophotometrically. Patients with selective IgA deficiency were found to be tTG IgA negative, but were positive for IgG tTG. However, IgG class tTG antibody was not specific for untreated coeliac disease in patients with normal quantities of serum IgA [7].

The tTG ELISA can be performed using human recombinant tTG [8]. Human tTG can be expressed in the human embryonic cell line 293-EBNA. After purification with streptavidin affinity chromatography, it can be used in the ELISA, giving a specificity of 98.1% and a sensitivity of 98.2%, versus a specificity of 95% and a sensitivity of 93% for guinea pig liver tTG [1].

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