Synthesis of novel lipidated iridoid glycosides as vaccine adjuvants: 6-O-Palmitoyl Agnuside elicit strong Th1 and Th2 response to ovalbumin in mice

Novel lipidated analogs of iridoids viz., Agnuside and Negundoside with different chain length were synthesized and tested for immune adjuvant activity in the presence of weak antigen ovalbumin. Based on in vitro assay, 6-O-palmitoyl Agnuside (AG-3) was further taken up for detailed in vivo activity and found to significantly enhance the production of anti OVA IgG titer, neutralizing antibody (IgG1 and IgG2a) titer as well as soluble mediators of a Th1 (IL-2, IFN-γ)/Th2 response (IL-4) and proliferation of T lymphocyte subsets (CD4/CD8) and co stimulatory molecules CD80/CD86. Furthermore, the SAR studies revealed that presence of acyl group at aglycon moiety of these iridoid glycosides is crucial for immune adjuvant activity.