Celiac disease, an autoimmune disorder of the samll intestine, is caused by a reaction to the gluten protein found in wheat and related grain species damaging nearby tissue. Celiac disease is difficult to diagnose, particularly in its early stages.

Patrick S. Daugherty, University of California, Santa Barbara, USA, and colleagues have developed a strategy to capture novel celiac disease antibodies by creating an enormous library of random peptide sequences. They inserted one billion random peptide genes into Escherichia coli, with one peptide gene per bacterium.

Antibodies from the blood of 22 celiac patients were labled with a green fluorescent dye and 22 of other patients with a red dye. The peptide-coated E. coli bacteria were mixed with these and unlabeled antibodies from 40 healthy volunteers in fivefold excess.
Cells labeled with both dyes displayed a peptide sequence that could bind to an antibody found in at least two people and which could be a marker for celiac disease.

The multiparameter flow cytometry (MPFC) resulted in a panel of six unique peptide sequences. These sequences, all of which do not bind to the known celiac antibodies, yielded 85 % sensitivity and 91 % specifity on a set of 60 samples not used for discovery. This nearly matches the values of existing diagnostic tests.

The method is applicable to diseases involving the immune system, including difficult-to-diagnose illnesses such as lupus, multiple sclerosis, and some cancers.

• Antibody Repertoire Profiling Using Bacterial Display Identifies Reactivity Signatures of Celiac Disease,
  Bradley N. Spatola, Joseph A. Murray, Martin Kagnoff, Katri Kaukinen, Patrick S. Daugherty,
  Anal. Chem. 2013.
  DOI: 10.1021/ac303201d