Intranasal immunisation of mice against Streptococcus equi using positively charged nanoparticulate carrier systems

In order to potentiate a strong immune response after mucosal vaccination with a low immunogenic S. equi enzymatic extract, two positively charged particulate delivery systems (liposomes and nanoparticles) were created. Positively surface charged particles were expected to efficiently bind to negatively charged cell membranes and facilitate antigen uptake. Phosphatidylcholine-cholesterol-stearylamine liposomes encapsulating S. equi antigens were prepared and dimensionated to 0.22±0.01μm with a polydispersity index <0.242, zeta potential of +12±4mV and an encapsulation efficiency of 13±3% (w/w). Chitosan nanoparticles were prepared by ionotropic gelation with sodium tripolyphosphate, presenting a particle size of 0.17±0.01μm with polydispersity index <0.362, zeta potential of +23±8mV and an encapsulation efficiency of 53±6% (w/w). Both encapsulation methods were recognised as innocuous once antigens structure remained intact after incorporation as assessed by SDS-PAGE. Intranasal immunisation of mice with both formulations successfully elicited mucosal, humoral and cellular immune responses. Mucosal stimulation was confirmed by increased sIgA levels in the lungs, being the chitosan nanoparticles more successful in this achievement probably due to their different mucoadhesive properties. Both formulations share the ability to induce Th1-mediated immune responses characterised by IFN-γ production and high IgG2a antibody titers as well as a Th2 immune response characterised mainly by IL-4 production and IgG1 antibodies.