Salivary IgA
Rationale and Clinical Validity
Immunoglobulin A (IgA) is the major antibody isotype produced in gut-associated lymphoid tissue (GALT) and is the most plentiful antibody found in saliva and intestinal secretions. IgA is thought to possess properties of both a neutralizing agent (binding and immune exclusion) and of a mucosal immunopotentiator inducing effector immune responses against invading pathogens.[8] Given the role of IgA in modulating gastrointestinal immunity, the measurement of salivary IgA is theoretically an appealing test. Patients with IBS are no more likely than healthy controls to have measurable abnormalities in their humoral immune function according to antibody assays of the serum or luminal aspirates.[9,10] No studies have been performed to examine the relationship between IBS and salivary IgA levels.
Analytical Validity
Salivary IgA may vary acutely with stress and with exercise,[11,12] hence isolated measurements may not reflect any putative underlying disease process. What is also missing are data correlating the level of salivary IgA with that in the lower gastrointestinal system—arguably levels of IgA may not even be reflective of potential abnormalities elsewhere.
Clinical Utility
Salivary IgA cannot be recommended as an investigation for gastrointestinal disease. Not only is the relationship between changes in IgA and gastrointestinal illness not established, but it is uncertain whether salivary IgA is reflective of IgA lower in the gastrointestinal system.
J Gastroenterol Hepatol. 2013;28(1):73-77. © 2013 Blackwell Publishing
