Methods of diagnosing celiac disease in a subject are provided. In some embodiments, the method comprises contacting a sample of bodily fluid from the subject with an antigen comprising a recombinant or synthetic deamidated gliadin protein, wherein the deamidated gliadin protein comprises a hexamer of peptides each having the sequence of SEQ ID NO:1; and detecting an antibody from the sample that specifically binds to the antigen, thereby diagnosing celiac disease in the subject.