AbstractsBiology & Animal Science

Selective IgA deficiency (sIgAD) is the most common immunodeficiency in humans. Auto-reactive antibodies to human IgA are found in the serum of 20-40% of individuals with sIgAD. It is unknown whether these antibodies play a role in the pathogenesis of this immunodeficiency, and most researchers believe that they are secondary to the onset of sIgAD. However, it is possible that in these individuals, the anti-IgA antibodies are in fact responsible for the removal of IgA from serum, and are originally generated against xenogeneic IgA. To examine this hypothesis, the presence of anti-bovine and anti-human IgA antibodies was tested by ELISA in serum samples from IgA-deficient and control individuals. All 14 of the IgA-deficient individuals that were tested had IgG anti-bovine IgA antibodies (100%), whereas only 8 had IgG anti-human IgA antibodies (57%). Individuals with both anti-bovine and anti-human IgA antibodies always had a higher titre against bovine IgA than against human IgA. Of 18 control individuals who have normal serum levels of IgA and no anti-human IgA antibodies, a surprisingly high proportion (61%) had IgG anti-bovine IgA antibodies in their serum. These results strongly support the hypothesis that the anti-human IgA antibodies found in IgA-deficient individuals are originally produced against xenogeneic IgA, specifically bovine IgA found in dietary beef products. These antibodies can be found in many normal individuals, but only those that cross-react with endogenous human IgA will lead to the removal of IgA from circulation, and to sIgAD. Thus, sIgAD with anti-IgA antibodies is an acquired immunodeficiency, initiated by cross-reactive antibodies consumed in the diet.