Fate of plasmid DNA encoding infectious bursal disease virus VP2 capsid protein gene after injection into the pectoralis muscle of the chicken

The objective of this study was to determine whether recombinant plasmid DNA injected intra-muscularly into chickens expressed the gene of interest in vivo and could be subsequently detected in primary and secondary lymphoid tissues with polymerase chain reaction (PCR). The VP2 capsid protein gene of the standard challenge strain (STC) of infectious bursal disease virus (IBDV) was cloned into a eukaryotic plasmid, and purified DNA was prepared. Fourteen 2-wk-old chickens were injected in the pectoral musculature with 500 mug of plasmid DNA dissolved in sterile PBS. Seven chickens were similarly injected with PBS alone. Pectoral muscle, thymus, spleen, bursa of Fabricius, and cecal tonsils were collected at 12, 24, 36, 48, 72, 96, and 168 h postinjection for detection of protein expression (in muscle) and to extract total DNA for PCR amplification of the VP2 capsid gene. Expression of VP2 was demonstrated in muscle tissue at 12 and 24 h postinjection by using an indirect immunofluorescence assay. PCR amplification with primers specific for the VP2 gene showed that the DNA was present in the thymus, spleen, and bursa of Fabricius but not in cecal tonsils. These results demonstrate that plasmid DNA injected directly into the pectoral muscle of chickens is transcribed and translated at the injection site and promptly distributed to primary and secondary lymphoid tissues.