Size effect of mesoporous silica nanoparticles on regulating the immune effect of oral influenza split vaccine.

Mucosal immunization is a powerful weapon against viral infection. In this paper, large pore mesoporous silica nanoparticles (LMSN) with different particle sizes were synthesized for loading influenza split vaccine (SV) to explore the effect of nanoparticle sizes on mucosal immunization and adjuvant efficacy. Interestingly, it was found that among the three particle sizes of nanoparticles, only LMSN-M with around 250 nm could significantly enhance the mucosal immune effect of SV, possessing adjuvant effect. The results indicated that particle size affected the adjuvant effect of LMSN. There was no apparent difference in vaccine loading capacity of LMSN with different particle sizes, but the release of SV depended on the pore length of LMSN. The adjuvant effect of LMSN-M was attributed to its higher cellular uptake performance, intestine absorption and transport efficiency, and the ability to stimulate the maturation of dendritic cells. Simultaneously, compared with LMSN-S and LMSN-L, the more retention of LMSN-M in mesenteric lymph nodes increased the chance of interaction between vaccine and immune system, resulting in the enhanced immunity. This is the first time to study the impact of particle size of LMSN adjuvant on improving mucosal immunity of oral influenza vaccine, and the present work provides a scientific reference for adjuvant design of oral vaccine.