Secretory immunoglobulin A (sIgA) is the major antibody of the body's mucous membranes exposed to the outside world, such as the nose and lungs (exposure to air) and the intestinal epithelium (exposure to food). Secretory IgA is an important part of the immune system that protects the body at specific sites from harmful bacteria or viruses that could come in contact with the body and cause disease. Optimal sIgA levels keep the intestinal epithelium strong and healthy and are part of a strong immune system.
Secretory IgA serves as the first line of defense to protect the intestinal epithelium from toxins and pathogenic microorganisms. Through a process known as immune blockade, sIgA helps remove antigens and pathogens from the intestinal tract by blocking their access to epithelial cell receptors, trapping them in the mucus, and facilitating their removal with the help of peristaltic movements and the ciliated epithelium. In addition, secretory IgA is involved in mucosal immunity and intestinal homeostasis through mechanisms that have only recently been discovered. Secretory IgA has the ability to directly address microbial infectious agents, to affect the composition of the intestinal microbiome through various mechanisms, to promote the transport of antigens along the intestinal epithelium towards dendritic cells of lymphatic tissue, and finally, to suppress pro-inflammatory responses usually associated with pathogenic microbes and allergens.
Why is secretory IgA testing important?
The measurement of secretory IgA in stool helps in assessing the function of the immune system both locally in the gastrointestinal tract (which accounts for approximately 70-80% of the total immune system) and 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.
More information on secretory IgA
Secretory immunoglobulin A (sIgA) consists of two IgA monomeric molecules attached to a molecule called a J-chain and another molecule called an additional secretory component. It is secreted by plasma cells located in the basal membrane of the mucous membranes. The synthesis of sIgA is independent of the synthesis of IgA circulating in the blood. This means that serum IgA deficiency is not related to sIgA deficiency. Secretory immunoglobulin A is the major immunoglobulin in saliva, tears, colostrum, nasal mucus, breast milk, tracheobronchial secretions, and the gastrointestinal tract. It plays an important role in preventing the attachment of microorganisms to the mucous membranes, activating the alternative pathway of the supplement, and activating the inflammatory reactions. Newborns receive sIgA in breast milk and are thus "vaccinated" passively against gastrointestinal infections.