Sera from patients with autoimmune diseases do not have circulating IgA antibodies against tissue transglutaminase

After the identification of tissue transglutaminase (TGc) as the predominant endomysial autoantigen of coeliac disease and dermatitis herpetiformis, diagnostic ELISAs were produced. Sera from patients with a broad spectrum of autoimmune diseases or with nonautoimmune diseases involving enhanced apoptosis, cell lysis and/or putative secondary autoimmune processes showed false positive reactions in these assays, as detected by a number of investigators. Sera from 605 patients and controls were tested in a human TGcELISA including 304 patients with autoimmune and 122 with other diseases. Anti-gliadin and anti-endomysium antibodies were also determined in 70 patients chosen at random. Overall 49% of all autoimmune sera were false positive in the human TGc ELISA. The difference between the median titers of the autoimmune and the control sera was significant in every case except for the pemphigus vulgaris sera (bullous pemphigoid, p¼0.012;pemphigus vulgaris, p¼0.152; SLE, p¼0.0005; antiphospholipid syndrome, p¼0.0002; for each of the other groups po0.0001). Significant differences were also found in serum titers between controls and patients with hepatitis C (po0.0001), psoriatic arthritis (p¼0.0065),and malignancies (p¼0.0005). Altogether 25% of the sera from patients with hepatitis C, psoriatic arthritis, and malignancies were positive in the human TGc ELISA. In contrast, testing 70 of the false positive patients for total serum IgA levels, AGA and EMA reactivity as well as immunoblots showed that no association of these conditions with gluten sensitive enteropathy can be confirmed. However, further purification of the TGc protein preparation used for coating and elevation of ionic strength in the buffers could eliminate false positive signals.The currently used method for TGc ELISA allows nonspecific positivity of certain sera from patients having circulating IgA of high affinity against impurities. Thus it is evident that positivity of a TGc ELISA should not alone be taken as the basis for a diagnosis of coeliac disease or dermatitis herpetiformis

Tissue transglutaminase ELISA positivity in autoimmune disease independent of gluten-sensitive disease

Background Our aim was to understand why some sera from patients with a broad spectrum of autoimmune diseases or non-autoimmune diseases involving enhanced apoptosis, cell lysis and/or putative secondary autoimmune processes show reactions in the tissue transglutaminase (TGc) ELISA used for diagnosis of gluten-sensitive disease.Methods Sera were compared from groups of patients with autoimmune diseases, diseases involving organ specific enhanced cell death, celiac disease or dermatitis herpetiformis, diseases of non-autoimmune origin, and a group without known disease. IgA antibodies against TGc were detected using human antigen (produced recombinantly in bacterial or human cells) in different systems (non-commercial ELISA with buffers of differing NaCl concentrations, and anti-TGc sandwich ELISA). Anti-gliadin and anti-endomysium antibodies were also determined.Results Many sera from patients with autoimmune disorders gave a positive signal in the human TGc ELISAs. The signal appeared related to minor impurities in the recombinant human TGc used and to raised serum IgA antibody levels rather than to the occurrence of TGc specific antibodies in these patients.Conclusions No association of anti-TGc Abs and autoimmune conditions independent of gluten-sensitive disease could be shown. Care should be taken to exclude copurification of chaperones, like heat shock protein 70, where preparing antigens for TGc ELISAs.Keywords: Tissue transglutaminase; Celiac disease; Gluten-sensitive disease; Autoimmunity; ELISA<br/