The GI tract serves a vital function by excluding the uptake of enteropathogens, which is accomplished in large part by the antigen binding activity of the immunoglobulin secretory IgA. The humoral immune status of the GI tract can be assessed by determining the fecal concentration of sIgA. The sIgA secreted by mucosal-associated lymphoid tissue, represents a pivotal and specific line of defense of the GI mucosa, along with such nonimmune factors as mucins and lactoferrin. 1 As the principal immunoglobulin isotype present in mucosal secretions, sIgA plays an important role in controlling the intestinal milieu, which is constantly presented with potentially harmful antigens such as pathogenic microorganisms, abnormal cell antigens, and allergenic proteins.
Secretory IgA has been shown to bind to toxin A from Clostridium difficile, preventing its interaction with the brush border of the intestines. 2 Other studies indicate that sIgA prevents Vibrio cholera from adhering to the intestinal mucosa. 3
Deficiencies in sIgA have been associated with increased absorption of food protein antigens as well as with lowered resistance to intestinal infection, including yeast overgrowth. In instances where sIgA is low, there is increased risk for adhesion and proliferation of pathogenic organisms, and for associated damage to the intestinal mucosa. Levels higher than reference range have been associated with atopic dermatitis, 4 dysbiosis, increased exposure to pathogenic organisms and toxins, and increased exposure to allergens. 5
1 Mestecky J, Russell MW. Passive and active protection against disorders of the gut. Vet Q . 1998;20(3):S83-7.
2 Dallas SD, Rolfe RD. Binding of Clostridium difficile toxin A to human milk secretory component. J Med Microbiol , 1998;47:10, 879-88.
3Cash RA, Musci SI, Libonati JP, et al.Response of man to infection with Vibrio cholera: protection from illness afforded by previous disease and vaccine.J Infect Dis. 1974;130:325-33.
4 Voltz JM, Mole C, Aubin F, et al. Serum and salivary immunoglobulins A in atopic dermatitis: prospective and comparative case control study. Ann Dermatol Venereol . 1998;125:2, 100-4.
5Ikura M, Yamaguchi M, Fujisawa T, et al. Secretory IgA induces degranulation of IL-3-primed basophils. J Immunol . 1998;161:3, 1510-5.
Secretory lgA, stool