Abstract
One of the key benefits in using chickens for immunization is the high yield of antibodies obtainable. It is known that egg production decreases over time, while animal maintenance costs remain stable. It would, however, be desirable to keep hens as long as possible to obtain maximal amounts of antibodies. To identify a suitable length of time that animals can be kept and to optimize the cost:yield ratio, we monitored the number of eggs laid, the total amount of chicken IgY, and the specific antibody titer from individually prepared eggs over a 2-yr period. The plant toxin ricin and the Clostridium botulinum neurotoxins type A and B were used to immunize 4 chickens. The number of eggs laid in 2 yr was approximately 600 per hen (about 80% of the maximum egg number), yielding about 20 to 40 g of total IgY per hen. A stable antibody titer of 1:100,000 to 1:1,000,000, as measured by ELISA, was obtained following up to 11 injections of 10 to 20 microg of immobilized native toxin. Laying capacities were found to decrease, on average, from 7 eggs/wk at the point of first immunization to 2 eggs/wk after more than 2 yr. In parallel, the yield of total and specific IgY increased over time, so that the antibody recovery remained high, even after prolonged immunization times. Using purified IgY preparations, classical immunological assays such as ELISA and Western blotting were performed. Furthermore, the IgY showed neutralizing capacity when used to block the functional activity of the toxins both in vitro and in vivo. Analysis of the total IgY content over time demonstrated a complex biological oscillation (and the antigen-specific titer), with a shorter time period of around 7 d (circaseptan rhythm). In summary, we successfully immunized chickens with ricin and botulinum neurotoxins and monitored laying capacity, IgY concentration, and specific antibody titer over an extended period of 2 yr.