Enhancement of anamnestic immunospecific antibody response in orally immunized chickens

Production of immunospecific egg yolk antibodies (IgY antibodies) in egg laying hens through oral immunization is an attractive alternative to conventional antibody production in mammals for economic reasons as well as for animal welfare reasons. Oral immunization results in a systemic humoral response, but oral booster immunizations lack efficiency. The aim of the present study was to develop immunization schemes in which the concentration of immunospecific IgY would increase following oral booster immunizations. Two groups of egg laying hens (5 in each group) were immunized orally (each immunization event consisted of dosing on three consecutive days) with Bovine Serum Albumin (BSA) in combination with RhinoVax® (RV) using different immunization schemes. A 3rd group served as a reference and received BSA emulsified in Freund's Incomplete Adjuvant (FIA) by subcutaneous injection three times and one oral dose with BSA + RV. The eggs of the chickens in this group had a significantly higher immunospecific anti BSA IgY-concentration than did any of the eggs from the orally immunized chickens. One of the immunization regimes (immunizations in weeks 1, 7 and 18) clearly included a booster effect of the immunization in week 18, demonstrating the presence of memory cells following the two initial oral immunizations. Considering that oral immunization results in approximately ten times lower concentrations of immunospecific antibodies in the egg yolk, compared to traditional subcutaneous immunization schemes, the oral immunization routines have to be further refined to compete with parenteral immunization protocols.