title: Calcium activation of tissue transglutaminase in radioligand binding and enzyme-linked autoantibody immunoassays in childhood celiac disease.
abstract: BACKGROUND
  Conflicting data have been published concerning the effect of calcium on binding of autoantibodies to tissue transglutaminase (tTG) in celiac disease (CD).
  
  
  METHODS
  IgA-tTG and IgG-tTG were measured with radioligand binding assays (RBA) using human recombinant (hr) (35)S-tTG produced in lysate of rabbit reticulocytes and with guinea pig (gp) tTG ELISA in 51 CD children (median: 5.7 years) and 35 controls (median: 2.2 years). Assays were performed with and without calcium.
  
  
  RESULTS
  In hr-tTG RBA, IgA-tTG levels remained unchanged after calcium detecting 50/51 CD children and 1/35 controls (p<0.0001). IgG-tTG levels decreased with calcium (p<0.0001) in CD children and detected 48/51 with and 49/51 without calcium as compared to 1/35 controls (p<0.0001). In gp-tTG ELISA, levels increased with calcium (p<0.0001) making it possible to detect an additional three to a total of 50/51 with IgA-tTG and 13 to 39/51 CD children with IgG-tTG compared to 4/35 and 8/35 controls (respectively, p<0.0001). Rabbit reticulocytes displayed calcium-dependent tTG activity.
  
  
  CONCLUSIONS
  Calcium increased binding of IgA-tTG and IgG-tTG in the ELISA test. The reverse effect observed in RBA may be explained by competitive binding between calcium activated native rabbit reticulocyte tTG and hr (35)S-tTG. tTG autoantibody assays may need taking calcium into account for accurate diagnostic sensitivity and specificity for CD.
authors.affiliation: Department of Pediatrics, University Hospital MAS, Lund University, S-205 02, Malmö, Sweden. daniel.agardh@home.se
authors.forename: Daniel
authors.initials: D
authors.lastname: Agardh
authors.forename: Bodil
authors.initials: B
authors.lastname: Roth
authors.forename: Ake
authors.initials: A
authors.lastname: Lernmark
authors.forename: Pål
authors.initials: P
authors.lastname: Stenberg
mesh_terms: D000293:Adolescent; D000328:Adult; D001323:Autoantibodies / Q000097:blood; D002118:Calcium / Q000276:immunology*; D002446:Celiac Disease / Q000175:diagnosis* / Q000201:enzymology* / Q000276:immunology; D002648:Child; D002675:Child, Preschool; D003937:Diagnosis, Differential; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods*; D005260:Female; D019204:GTP-Binding Proteins / Q000276:immunology*; D006801:Humans; D007070:Immunoglobulin A / Q000097:blood; D007074:Immunoglobulin G / Q000097:blood; D007223:Infant; D008297:Male; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011869:Radioligand Assay / Q000379:methods*; D012680:Sensitivity and Specificity; D011503:Transglutaminases / Q000276:immunology*
chemical_list: D001323:Autoantibodies; D007070:Immunoglobulin A; D007074:Immunoglobulin G; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D019204:GTP-Binding Proteins; D002118:Calcium