Mucosal Vaccination Using Polyacryl Starch Microparticles as Adjuvant with Salmonella enteritidis as a Model Pathogen

Polyacryl starch microparticles have been developed as a new mucosal vaccine adjuvant intended for use in oral vaccination. The main objectives of this thesis were to evaluate the efficacy of these polyacryl starch microparticles and to study their uptake through mucosal tissues. Secreted or surface components of Salmonella enterica serovar Enteritidis were used in free form or were conjugated to or mixed with the microparticles in vaccination studies in mice in order to find components suitable for use in a future combination vaccine against enteric bacteria such as enterotoxigenic Escherichia coli. The immune response elicited using secreted proteins from S. enterica serovar Enteritidis was shown to be mainly directed against flagella-related antigens and partly by LPS. Flagellin was purified and used in C3H/HeJ mice that do not respond to LPS. Strong immune responses were observed even when the flagellin was given orally alone. Recombinant Salmonella atypical fimbriae (SafB/D) complexes, a conserved structure within Salmonella species, were also studied and shown to be immunogenic after administration both subcutaneously and nasally, but not orally. Oral challenge using live bacteria, showed that mice orally immunised with the secreted antigens, resulted in a lower degree of infection than that seen in non-vaccinated mice. Similarly, mice that had been immunised with purified free flagellin had a lower degree of infection than untreated mice. However, with mice, immunised with SafB/D complexes plus rCTB, only the subcutaneous route resulted in a lower degree of infection than seen in untreated mice. The polyacryl starch microparticles were effective as an adjuvant with secreted proteins, but did not potentiate the immune response in the study using flagellin. Confocal laser-scanning and transmission electron microscopy demonstrated that the microparticles were taken up by pig respiratory nasal mucosa mounted in horizontal Ussing chambers. Although anticytokeratin 18 stained mucus-producing cells, M cells were not seen in the studied area. Changing the route of administration of the microparticles conjugated with serum albumin can cause differences in the IgG-subclass ratios. The mucosal immune response measured as specific s-IgA levels, was induced by oral but not parenteral immunisation