Enhanced mucosal and systemic immune responses obtained by porous silica nanoparticles used as an oral vaccine adjuvant: Effect of silica architecture on immunological properties

Three different kinds of silica (S2, S1 and SBA-15) with different particle sizes (130, 430   nm and 1–2   μm) and different pore characteristics (i.e. pore size and shape) were developed as oral vaccine immunological adjuvants and the relationship between the silica architecture and immunological properties was investigated. The silica particles were characterized using SEM, TEM and nitrogen adsorption. Model antigen bovine serum albumin (BSA) was successfully entrapped into the silica pores to produce a sustained release vaccine delivery system. Compared with the responsiveness induced by parenteral administration of BSA emulsified in Freund's complete adjuvant (FCA), oral immunization with the silica/BSA formulation produced a stimulated humoral and mucosal (sIgA) response. The IgG and IgA titers induced by loading BSA was as follows: S1   >   S2   >   SBA-15. The highest IgG and IgA titers of S1 were attributed to its large honeycombed pores and the optimal particle diameter of 430   nm. The corresponding IgG1 and IgG2a titers were also investigated to confirm that BSA loaded in nanoparticles by oral immunization can induce both T-helper 1- and T-helper 2- (Th1 or Th2) mediated responses. We believe that the results of our research will open up new avenues for the formulation of oral vaccines.