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Salivary Secretory Immunoglobulin A

Salivary Secretory Immunoglobulin A

Secretory Immunoglobulin A (SIgA) is a subclass of Immunoglobulin A (IgA), an antibody that plays a critical role in mucosal immunity.  SIgA is the main immunoglobulin found in mucous secretions from the tear glands, salivary glands, mammary glands, the respiratory system, the genito-urinary tract, and the gastrointestinal tract. (1) SIgA is not synthesized by mucosal epithelial cells in these structures or derived from blood.  Instead, it is produced by B-lymphocytes adjacent to the mucosal cells, then transported through the cell interiors, and released into the secretions from the cells. (2) SIgA plays a key role in protecting vulnerable areas such as the oral cavity, lungs, and gut from invading pathogens. (1)  Differences in SIgA levels in the saliva from different glands have been observed in humans, with the highest levels found in the minor saliva glands. (2,3)  SIgA exhibits a diurnal rhythm, decreasing from the highest levels in the morning to the lowest in the evening. (4) Levels of SIgA in saliva vary in response to physical and psychological stress through interactions with the autonomic nervous system. (5,6)  SIgA levels in saliva are affected by flow rates, with concentrations normally decreasing as flow rates increase.  Measurement of flow rates is advisable in order to express SIgA secretion as a function of time. (6)