Mucosal Adjuvant Potential of Quillaja saponins and Cross-linked Dextran Microspheres, Co-administered with Liposomes Encapsulated with Tetanus Toxoid

Intranasal vaccination is particularly a striking route for mucosal immunization, due to the ease of administration and the induction of both mucosal and humoral immunity. However, soluble antigens (Ag) are not sufficiently taken up after the nasal administration and need to be co-administered with adjuvants, penetration enhancers or encapsulated in particles. So, in this study, tetanus toxoid (TT) as a model Ag was entrapped in nonionic liposomes. The effect of the co-administration of Quillaja saponin (QS) as an adjuvant and cross-linked dextran microspheres (CDM) as penetration enhancer on immune responses was also studied. TT or TT + QS loaded liposomes were prepared by dehydration-rehydration method (DRV), followed by the extrusion through 400 nm filters. Some formulations were mixed with CDM. Liposomes were first characterized for their size range, mean diameter and morphology using particle size analyzer, optical and transmission electron microscopes. The volume mean diameter of liposomes was determined as 3836 ± 179 and 624 ± 114 nm before and after the extrusion, respectively. Structural efficiency of TT extracted from liposomes was confirmed by SDS-PAGE method. Encapsulation efficiencies of TT and QS were 44 ± 8.50% and 60 ± 6.02%, respectively. Rabbits were nasally immunized with various formulations and serum IgG titers and nasal lavage sIgA titers were determined by an ELISA method. TT + QS liposomes induced higher sIgA levels in comparison with TT liposomes (p < 0.05), but the difference in serum IgG levels was not significant. Results indicated that neutral liposomes administered nasally, have a good potential for induction of mucosal immunity and co-encapsulation of QS and TT in liposomes improved the systemic and mucosal immune responses.