THE IMMUNE SYSTEM AND IGA DEFICIENCY - THE FUNCTION OF IGA IN THE BODY Immunoglobulin A, or IgA, is an antibody produced in the mucosal lining and plays a role important in mucosal immunity. More IgA is produced in the mucosal linings than all other types of antibodies combined. The amount of IgA produced contributes greatly to total immunoglobulin production, and approximately three to five grams of IgA are secreted into the intestinal lumen each day. IgA is divided into two subclasses, IgA 1 and IgA 2, and can also exist in a dimeric form called secretory IgA, sIgA. IgA1 is the predominant subclass found in serum. In most lymphoid tissues, cells that produce IgA predominate. The rate of IgA2 production is greater in secretory lymphoid tissues than in non-secretory lymphoid organs (spleen, peripheral lymph nodes, etc.). In IgA2, the heavy and light chains are linked with noncovalent bonds instead of disulfide. The secretory form of IgA, sIgA, is the main immunoglobulin present in mucous secretions such as colostrum and in secretions of the genitourinary tract, gastrointestinal tract, prostate and respiratory epithelium, tears and saliva (which is important when testing levels of IgA due to IgA deficiency which will be discussed later in this article) and also in small quantities of blood. The secretory component of sIgA protects the immunoglobulin from degradation by certain enzymes and makes sIgA able to survive in the hostile environment of the gastrointestinal tract and thus provide protection against microbes that multiply in body secretions. Secretory IgA can also inhibit the inflammatory effects of other immunoglobulins (National Library of Medicine, 2011). As stated above, IgA plays a critical role... the focus of the article... Primary Immunodeficiency Diseases Patient and Family Manual - Selective IgA Deficiency. 5th ed. Maryland, USA.Izenberg, Neil MD. 2011. Children's Health, Immune System. [ONLINE] Available at: http://kidshealth.org/parent/general/body_basics/immune.html#. [Accessed 4 Mar 14].Jeffry Modell Foundation, Primary Immunodeficiency Resource Center. 2013. Primary immunodeficiency diseases - Selective IgA deficiency. [ONLINE] Available at: http://kidshealth.org/parent/general/body_basics/immune.html#. [Accessed 2 Mar 14]. National Library of Medicine - Medical Subject Headings. 2011. Immunoglobulin A. [ONLINE] Available at: http://www.nlm.nih.gov/cgi/mesh/2011/MB_cgi?mode=&term=Immunoglobulin+A. [Accessed 24 April 14].Worldbook. 2014. Fibroblast Research. [ONLINE] Available at: http://worldbookonline.com/advanced/dict?lu=fibroblast. [Accessed 26 April 14].