Assessment of the adjuvant activity of mesoporous silica nanoparticles in recombinant Mycoplasma hyopneumoniae antigen vaccines

The adjuvant potential of two mesoporous silica nanoparticles (MSNs), SBa-15 and SBa-16, was assessed in combination with a recombinant HSP70 surface polypeptide domain from Mycoplasma hyopneumoniae, the etiological agent of porcine enzootic pneumonia (PEP). The recombinant antigen (HSP70212-600), previously shown as immunogenic in formulation with classic adjuvants, was used to immunize BALB/c mice in combination with SBa-15 or SBa-16 MSNs, and the effects obtained with these formulations were compared to those obtained with alum, the adjuvant traditionally used in anti-PEP bacterins. The HSP70212-600 + SBa-15 vaccine elicited a strong humoral immune response, with high serum total IgG levels, comparable to those obtained using HSP70212-600 + alum. The HSP70212-600 + SBa-16 vaccine elicited a moderate humoral immune response, with lower levels of total IgG. The cellular immune response was assessed by the detection of IFN-γ, IL-4 and IL-10 in splenocyte culture supernatants. The HSP70212-600 + SBa-15 vaccine increased IFN-γ, IL-4 and IL-10 levels, while no stimulation was detected with the HSP70212-600 + SBa-16 vaccine. The HSP70212-600 + SBa-15 vaccine induced a mixed Th1/Th2-type response, with an additional IL-10 mediated anti-inflammatory effect, both of relevance for an anti-PEP vaccine. Alum adjuvant controls stimulated an unspecific cellular immune response, with similar levels of cytokines detected in mice immunized either with HSP70212-600 + alum or with the adjuvant alone. The better humoral and cellular immune responses elicited in mice indicated that SBa-15 has adjuvant potential, and can be considered as an alternative to the use of alum in veterinary vaccines. The use of SBa-15 with HSP70212-600 is also promising as a potential anti-PEP subunit vaccine formulation.