Immunoglobulin Knockout Chickens Lack Detectable Circulating IgA in Response to Keyhole Limpet Hemocyanin Vaccination

Abstract

Immunoglobulin knockout chickens have a unique potential for use as a research tool. One could examine the contribution of immunoglobulins to pathogen resistance or further characterize the nutritional implications of mounting an immune response. Researchers have attempted to examine the effects of eliminating antibody production in chickens by ablation of the bursa of Fabricius. These techniques cause a loss of patency of the cloaca causing leakage of rectal contents. This results in continuous diarrhea and complications with dehydration and hygiene. Thus, knockout chickens are a superior model because the bursa is maintained, which eliminates the hygienic complications, while also eliminating immunoglobulin production. We examined chickens that were either heterozygous or homozygous for a knockout of the immunoglobulin heavy chain J gene segment. It was previously shown that heterozygotes but not homozygotes produce circulating IgY and IgM in response to vaccination, but IgA was not characterized. The goal of the present study was to affirm that IgA producing cells are also absent in the homozygotes. At 4 weeks of age, birds were injected intramuscularly with 300µg of keyhole limpet hemocyanin mixed 1:1 with complete Freund's adjuvant. A booster was administered at 5 and 6 weeks of age using incomplete Freund's adjuvant. Serum was collected via wing vein puncture at 6 and 8 weeks of age for IgA detection using a sandwich ELISA. It was found that circulating IgA was present in heterozygotes, but homozygotes had no detectable IgA concentrations. In conjunction with previous research showing homozygotes also lack circulating IgY and IgM, these results confirm that homozygotes lack all major classes of circulating immunoglobulin known in chickens.