SIGA (Secretory IgA) is the primary antibody that is protecting us from pathogens and toxins from penetrating mucosal surfaces. Its role is crucial in protecting the integrity of the intestinal epithelium. The antibody blocks the access to the epithelial receptors and traps pathogens and toxins in the mucus which are then excreated by peristaltic movements.
SIgA has been identified to potentially neutralize virulence factors, modulate intestinal microbiota by Fab-dependent and -independent mechanisms, promote dendritic cell (DC) recruitement across the epithelial barrier and also down-regulate pro-inflammatory responses normally associated with the uptake of highly pathogenic bacteria and potentially allergenic antigens.
Multiple cytokines, including IL-4, TGF-β, IL-5, IL-6, IL-10 are instrumental in intestinal stimulating SIgA production. A subset of these cytokines, notably TGF-β and IL-10, are also required for maintaining mucosal tolerance, thus establishing one of the many links between SIgA production, immunity and intestinal homeostasis.
Considerations for low fecal sIgA:
Because of the lack of clinical evidence, there is no clear cut-off value for low fecal sIgA. People with systemic IgA deficiency can have low levels of fecal secretory IgA. There is a demonstrated link between IgA deficiency and several GI diseases, including:
- celiac disease,
- nodular lymphoid hyperplasia,
- ulcerative colitis,
- Crohn’s disease,
- pernicious anemia,
- and gastric and colonic adenocarcinoma.
Low sIgA may reflect a loss of GI immune response resiliency. Fecal sIgA may be low in severe/prolonged IBD patients due to a switch from intestinal IgA to IgG production as well as a deficiency in producing IgA dimers and polymers.
Secretory IgA demonstrates an array of activities integral to the maintenance of intestinal homeostasis. It influences the composition of intestinal microbiota, down-regulates pro-inflammatory responses normally associated with the uptake of highly pathogenic bacteria and potentially allergenic antigens, and promotes the retro-transport of antigens across the intestinal epithelium to gut-associated lymphoid tissue (GALT). Therefore, a low sIgA is clinically significant.
The test result should be considered together with any other medical condition, other biomarkers, and microbiome profiles when interpreting the data.
Causes of elevated fecal sIgA:
- Any defective epithelial barrier
- A defective epithelial barrier allows bacterial and microbial penetration, which is the strongest stimulator of sIgA production.
- Celiac disease
- Colon cancer
- IBS (especially the diarrhea subtype)
Therapeutic considerations for elevated fecal sIgA:
Assess for and treat root causes of immune upregulation /inflammation:
- Infection (bacterial, parasitic, and/or viral pathogen, potential pathogen)
- Compromised intestinal barrier function (i.e., intestinal permeability)
- Heightened response to noninfectious stimuli (i.e., food sensitivity/allergy, etc.)
Consider Food Antibody testing – If positive, consider elimination diet
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