Effect of priming/booster immunisation protocols on immune response to canine parvovirus peptide induced by vaccination with a chimaeric plant virus construct.

Expression of a 17-mer peptide sequence from canine parvovirus expressed on cowpea mosaic virus (CPMV) to form chimaeric virus particles (CVPs) creates vaccine antigens that elicit strong anti-peptide immune responses in mice. Systemic (subcutaneous, s.c.) immunisation and boosting with such CVP constructs produces IgG(2a) serum antibody responses, while mucosal (intranasal, i.n.) immunisation and boosting elicits intestinal IgA responses. Combinations of systemic and mucosal routes for priming and boosting immunisations were used to examine their influence on the level, type and location of immune response generated to one of these constructs (CVP-1). In all cases, s.c. administration, whether for immunisation or boosting, generated a Th1-biased response, reflected in a predominantly IgG(2a) serum antibody isotype and secretion of IFN-gamma from in vitro-stimulated lymphocytes. Serum antibody responses were greatest in animals primed and boosted subcutaneously, and least in mucosally vaccinated mice. The i.n. exposure also led to IFN-gamma release from in vitro-stimulated cells, but serum IgG(2a) was significantly elevated only in mice primed intranasally and boosted subcutaneously. Peptide- and wild-type CPMV-specific IgA responses in gut lavage fluid were greatest in animals exposed mucosally and least in those primed and boosted subcutaneously or primed subcutaneously and boosted orally. Lymphocytes from immunised mice proliferated in response to in vitro stimulation with CPMV but not with peptide. The predominant secretion of IFN-gamma from all immunising/boosting combinations indicates that the route of vaccination and challenge does not alter the Th1 bias of the response to CVP constructs. However, optimal serum and intestinal antibody responses were achieved by combining s.c. and i.n. administration.