IgE and IgG antibodies to food antigens in sera from normal dogs, atopic dogs and dogs with adverse food reactions
Authors: Halliwell R. E. W. , Gordon C. , Horvath C. , Wagner R. 
Published: August 2004

This study evaluated the antibody response to food antigens in three well‐defined canine populations. Food antigen‐specific IgE was measured in sera from: 24 normal dogs (age 9 months to 13 years, mean 5 years) (Group 1); 30 dogs with confirmed atopic dermatitis (CAD), all of whom failed to respond to a 6‐week home‐prepared hypoallergenic diet trial (age 9 months to 8 years, mean 3.3 years) (Group 2); and 23 dogs with adverse food reactions (age 1–12 years, mean 5 years) (Group 3). All Group 3 dogs had dermatological signs responsive to an 8‐week food trial using a commercial diet with capelin and tapioca; signs relapsed upon reinstitution of the original diet. Seven dogs additionally had diet‐responsive intermittent or continual loose stools. The ELISA employed 19 (18 in the case of IgG) crude or purified food antigens. IgE was detected with a monoclonal anti‐IgE antibody. IgG was detected with Fc‐specific polyclonal anti‐IgG. In the case of antigen‐specific IgG, 16 sera from Group 1, 16 from Group 2 and 13 from Group 3 only were assessed as sera had become depleted. Results were expressed as relative antibody units (RAU) by reference to standards included on each plate with a high level of IgE or IgG to the relevant antigen, and considered as positive if the RAU value was at least 50% greater than the end point of the standard curve. Overall, IgE results were positive to 3.49% of antigens in Group 1, 7.12% in Group 2 and 15.9% in Group 3. Multisensitive sera were largely confined to Group 3, with 22.65% showing positive results to four or more antigens as compared to 6.24% of Group 2 and 0% of Group 1. IgE RAU values were generally highest in Group 3 and lowest in Group 1, with Group 2 being intermediate. Results for Group 3 were significantly higher than those for Group 1 in the case of 12 of 19 antigens (Kruskal–Wallis test), with the reverse situation in two of 19 antigens. Group 3 IgE RAU values were significantly greater than those for Group 2 in nine of 19 antigens, with the reverse in nine of 19 antigens. IgG results showed similar trends, but greater discrimination between groups. The mean rank for Group 3 was higher than both Groups 1 and 2 for 17 of 18 antigens. Group 3 IgG RAU values were significantly higher than Group 1 values for 12 of 18 antigens (P < 0.01 for 10 antigens, and P < 0.001 for five antigens), and higher than Group 2 values for four of 12 antigens. Group 2 IgG values were significantly greater than those for Group 1 in the case of five of 18 antigens. In conclusion, the three populations differed markedly in their responses to food antigens, with the IgG responses being more discriminatory than IgE. The results were not confirmed by specific, individual antigen challenge studies, but neither are such studies undertaken with environmental allergens in CAD. Nonetheless, they suggest that serology to food antigens may be of value in identifying suitable candidates for hypoallergenic diet trials and in selecting a suitable diet. Funding: Waltham Centre for Pet Nutrition.