Abstract
Alpha-Galactosylceramide (alpha-GalCer) effectively activates the natural killer T (NKr) cells to secrete remarkable amounts of Th1 and Th2 cytokines and therefore, acts as a potential immunoadjuvant in vaccine formulation. In the present study, we prepared alpha-GalCer-bearing or alpha-GalCer-free liposomes and loaded them with Middle East Respiratory Syndrome Coronavirus papain-like protease (alpha-GalCer-Lip-MERS-CoV PLpro or Lip-MERS-CoV PLpro). These formulations were injected in mice to investigate the antigen-specific humoral and cell-mediated immune responses. The immunisation with alpha-GalCer-Lip-MERS-CoV PLpro or Lip-MERSCoV PLpro did not induce any notable toxicity in immunised mice. The results demonstrated that mice immunised with alpha-GalCer-Lip-MERS-CoV PLpro showed greater antigen-specific antibody titre, switching of IgG isotyping to IgG2a subclass and higher lymphocyte proliferation. Moreover, the splenocytes from alpha-GalCer-Lip-MERS-CoV PLpro immunised mice secreted greater levels of IFN-gamma, IL-4, IL-2 and IL-12. Interestingly, a booster dose induced stronger memory immune responses in mice previously immunised with alpha-GalCer-Lip-MERS-CoV PLpro. In summary, alpha-GalCer-Lip-MERS-CoV PLpro may prove to be a promising vaccine formulation to protect the individuals against MERS-CoV infection.