Secretory IgA (sIgA)

Secretory IgA (sIgA) is the principal antibody of the intestinal mucosa and the first line of defence against pathogens, toxins and food antigens. Low sIgA indicates weakened mucosal immunity — for example with prolonged strain (cortisol slows IgA production), altered gut flora or a lack of vitamin A or zinc. Measurable in the stool test.

What secretory IgA does in the body

Plasma cells in the gut lining produce IgA as a double molecule. The gut cells take it up on their underside via a dedicated receptor, transport it through the cell and release it on the gut side; part of the receptor remains attached to the antibody as the 'secretory component' and protects it from digestive enzymes. In the mucus on the gut surface, sIgA binds bacteria, viruses, toxins and food proteins and keeps them away from the gut cells without triggering inflammation. In this way it also helps shape the composition of the gut flora. Production is stimulated by contact with gut bacteria in the Peyer's patches, the lymphoid nodules of the small intestine; messengers such as TGF-beta and retinoic acid, made from vitamin A, control the switch of immune cells to IgA.

Low secretory IgA – what happens in the body?

When there is little sIgA in the gut, bacteria, toxins and food proteins are caught in the mucus less often and come into direct contact with the gut cells more often. The mucosal immune system then has to respond more strongly with inflammatory reactions, and pathogens can attach to the gut wall more easily – gastrointestinal infections occur more readily. The gut flora is also steered less. Low values occur with inherited selective IgA deficiency, malnutrition, a lack of vitamin A or zinc and with medications that suppress the immune system; studies have also measured less sIgA during prolonged strain, because cortisol slows IgA production.

High secretory IgA – what happens in the body?

A high value shows that the immune system of the gut lining is currently under heavy demand: the plasma cells produce more IgA because they encounter more pathogens, bacterial components or food proteins. This occurs with acute gut infections, with bacterial overgrowth or altered gut flora and with inflammation of the gut lining; studies have also observed it with a more permeable gut barrier. The value therefore shows an ongoing immune response, not its cause.

The interpretation is given in your report.