Tubular immunostimulating complex based on cucumarioside A2-2 and monogalactosyldiacylglycerol from marine macrophytes.

BACKGROUND: There is an urgent need to develop safe and effective adjuvants for the new generation of subunit vaccines. We developed the tubular immunostimulating complex (TI-complex) as a new nanoparticulate antigen delivery system. The morphology and composition of TI-complexes principally differ from the known vesicular immunostimulating complexes (ISCOMs). However, methodology for the preparation of TI-complexes has suffered a number of shortcomings. The aim of the present work was to obtain an antigen carrier consisting of triterpene glycosides from Cucumaria japonica, cholesterol, and monogalactosyldiacylglycerol from marine macrophytes with reproducible properties and high adjuvant activity. RESULTS: The cucumarioside A2-2 - cholesterol - MGalDG ratio of 6:2:4 (by weight) was found to provide the most effective formation of TI-complexes and the minimum hemolytic activity in vitro. Tubules of TI-complexes have an outer diameter of about 16 nm, an inner diameter of 6 nm, and a length of 500 nm. A significant dilution by the buffer gradually destroyed the tubular nanoparticles. The TI-complex was able to increase the immunogenicity of the protein antigens from Yersinia pseudotuberculosis by three to four times. CONCLUSIONS: We propose an optimized methodology for the preparation of homogeneous TI-complexes containing only tubular particles, which would achieve reproducible immunization results. We suggest that the elaborated TI-complexes apply as a universal delivery system for different subunit antigens within anti-infectious vaccines and enhance their economic efficacy and safety.

The influence of monogalactosyldiacylglycerols from different marine macrophytes on immunogenicity and conformation of protein antigen of tubular immunostimulating complex.

The tubular immunostimulating complex (TI-complex) is a novel nanoparticulate antigen delivery system consisting of cholesterol, triterpene glycoside cucumarioside A(2)-2, and glycolipid monogalactosyldiacylglycerol (MGDG) isolated from marine macrophytes. MGDG is crucial for the formation of a lipid matrix for the protein antigen incorporated in TI-complexes. Fatty acid composition and the physical state of this glycolipid depend on the taxonomic position of marine macrophytes. Therefore, the aim of the present work was to study the capacity of MGDGs, isolated from five species of marine macrophytes, to influence conformation and to enhance immunogenicity of porin from Yersinia pseudotuberculosis (YOmpF) as a model antigen of subunit vaccine based on TI-complexes. The trimeric porin was chosen for these experiments, because it was approximately two times more immunogenic than monomeric porin incorporated in TI-complexes. Immunization of mice with YOmpF within TI-complexes, comprised of different MGDGs, revealed a dependence of the immunostimulating effect of TI-complexes on the microvicosity of this glycolipid. TI-complexes comprising MGDGs from Sargassum pallidum and Ulva fenestrata with medium microviscosity induced maximal levels of anti-porin antibodies (four times higher when compared with those induced by pure porin). The adjuvant effect of TI-complexes based on other MGDGs varied by 2.8, 2.3 and 1.3 times for TI-complexes comprised of MGDGs from Zostera marina, Ahnfeltia tobuchiensis, and Laminaria japonica, respectively. MGDGs are also able to influence cytokine mechanisms of immunological regulation. DSC and spectroscopic studies showed that maximal immunostimulating effect of TI-complexes correlated with a moderate stabilizing influence of MGDGs from S. pallidum and U. fenestrata on the conformation of porin. The results obtained suggest lipid "nanofluidics" as a novel strategy for optimizing the immune response to protein antigens within lipid particulate systems.