Human Tissue Transglutaminase Elisa: A Powerful Mass Screening Diagnostic Assay for Coeliac Disease

95 Introduction: During the active phase of Coeliac disease (CD) a characteristics auto-antibody recognizing the endomysium (EmA) is produced. The antigen recognized by EmA has recently been identified as tissue transglutaminase (tTG). Aims: The aims of the study were: 1. To clone and express the human tTG (HTG) gene. 2. To develop an ELISA assay to measure IgA and IgG human tTG Ab. 3. To compare the sensitivity and specificity of HTG assay to the Guinea Pig tTG (GPTG) assay and to the EmA. Methods: We have cloned, expressed and purified HTG from the intestinal biopsy of a celiac patient. HTG was used in an ELISA assay in direct comparison to GPTG. The test population was 150 EmA negative controls and 86 EmA positive subjects. 2. subjects with IgA deficiency, and so EmA negative, were also tested. Results: An IgA ELISA on HTG was positive for 85/86 patients positive for IgA-EmA. The only one negative was negative by IgG ELISA as well. The two patients with IgA deficiency were found to be positive by IgG HTG ELISA. The sensitivity of this test was 97% for the IgA and 99% for IgA and IgG together. In contrast, the GPTG ELISA showed a sensitivity of 90% for IgA and 93% for IgA and IgG together. One false positive with GPTG and no false positives with HTG were obtained with the 150 EmA negative controls, giving a specificity of 100% for HTG and 99% for the GPTG. Discussion: These results show the diagnostic value of TG in general, and the HTG in particular, which is able to identify the 6% of CD patients missed by GPTG. One practical advantage of a HTG based ELISA, is the avoidance of the observer bias intrinsic to the identification of EmA by immunofluorescence, and the lack of technical difficulties compared to other methods. The almost absolute sensitivity and specificity of this simple test will allow mass screening in the general and at risk populations and may well lead to the discontinuation of intestinal biopsy for all, but the 1% of CD patients not identified, as has been previously proposed for EmA.