Pair Epitope Vaccination means vaccination of breeders and chicks by the same pathogen but with different epitopes.
Maternally derived antibodies (MDA) are critical for offspring protection during the first few days of life. The half-life of MDAs are short and their titers decline rapidly after the first week of age. MDA is protective in nature but they interfere in the development of immunity by vaccination or natural pathogen exposure. Because of this, there is a gap in chick’s life in which chick is at potential risk of infection from deadly pathogens. The gap in which there is no immunity is present inside chick is about 5 to 10 days. In this gap titer of MDA are lower than the critical protective threshold and the chick has yet to develop its own immunity against the vaccine. For this reason, a concept has been developed where day-old chick has to be vaccinated in the presence of MDAs.
(a) Mean NDV haemagglutination–inhibition antibody titre of commercial broiler flocks as a function of age. Each dot represents the average titre of 23 chicks. The solid line was fit to the data using local weighted regression to show the average age-dependent antibody levels.
The idea is to vaccinate mothers and their progeny with different neutralizing epitopes of the same pathogen. This thing will help in the chick to develop its own immunity against infection even in the presence of MDA for the same pathogen. Vaccination programs are very important as they defend flocks from various deadly diseases. Antibodies have to be developed by the avian immune system against pathogens. Antibodies are an important defence tool against viruses and antibody titers are positively correlated with protection.
(b). Conventional vaccination. Maternal breeders and offspring are vaccinated by the same set of antigens (Ag). Interference in the development of an immune response in the offspring causes delayed development of self-pathogen-specific antibodies and a susceptibility gap at a young age.
(c) Pair-epitopes vaccination. The maternal flock is vaccinated with one epitope of the pathogen, and the progeny with another set of epitopes. Consequently, antibodies transferred from the mother do not interfere with the induction of self-immunity, enabling overlap of a high level of MDAs and self-antibodies raised in response to 1-day vaccination, thus eliminating the gap in protection.
Breeder transfer protective antibodies to chicks which would be there for the first or second week of life. But these antibodies do not allow early vaccination. Early vaccination is necessary for strong long lasting protection against a particular pathogen. MDA inhibit B and T helper cells, antigen processing and activation of T suppressor cells. Such suppression of antibody and cellular immune responses has been reported for various viruses, including infectious bursal disease virus (IBDV) and Newcastle disease virus (NDV).
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