Secretory immunoglobulin A (sIgA) is a subclass of immunoglobulin A (IgA), an antibody that plays a critical role in mucosal immunity. Secretory immunoglobulin A is the major immunoglobulin found in the mucous secretions of the lacrimal glands, salivary glands, mammary glands, respiratory system, urogenital system, and gastrointestinal tract. Secretory immunoglobulin A is not synthesized by the epithelial cells of the mucous membranes of the aforementioned tissues and organs and is not derived from blood. Secretory immunoglobulin A is produced by B lymphocytes located near mucosal cells and then transported and released by specific cellular mechanisms of epithelial cells to extracellular secretions. Secretory IgA plays a key role in protecting vulnerable areas such as the oral cavity, lungs, and intestine from invasion by pathogens.
The secretion of sIgA shows a daily (circadian) rhythm, with the highest levels observed in the morning and the lowest in the evening. The levels of secreted immunoglobulin A in saliva vary depending on the physical and psychological stress through interactions with the autonomic nervous system. Salivary sIgA levels are affected by salivary flow rate, with its concentrations decreasing as the flow rate increases.
Why is it important to test the secretory Immunoglobulin A in saliva?
The usefulness of testing secretory IgA in saliva lies in assessing the function of the immune system both locally in the oral cavity and in the entire immune system. Elevated sIgA levels may indicate a strong immune response to an antigen or pathogen, while decreased sIgA levels are indicative of reduced mucosal immunity.
Saliva sIgA measurement is used to monitor athletes during periods of intense preparation to assess their susceptibility to infections or to investigate children with frequent upper respiratory tract infections or even as an indicator of environmental stress. Salivary IgA secretion levels have also been linked to the presence of tooth decay.
Decreased salivary IgA secretion is a common finding in patients with multiple sclerosis.