fig serum igg titers in groups и = for particles, n = for soluble of balbc mice immunized with either plgctabp gag dna of size nm or in or dna alone at two dose levels of xg and xg antibody titers are geometric mean titers ± se at weeks postsecond immunization week time point after immunizations at day and day the response from the nm and xm particles at both dose levels are not 50 didrex significantly different an important component of the adjuvant effect, since larger microparticles xm did not elicit a strong immune response the association of dna with nanoparticles 50 didrex and microparticles has been shown to be more effective than naked dna chitosandna particles nm of peanut allergen gene delivered orally, produced secretory iga and serum igga, compared with no detectable response with naked dna the pulmonary delivery of chitosandna particles average size of nm with plasmid dna encoding tcell epitopes from mycobacterium tuberculosis, were able to induce the maturation of dendritic cells and the increased level of ifny secretion, compared with the plasmid in solution or im delivery in another dna study, polylysinegraft imidazoleacetic acid complexed with dna with a diameter of nm was used for the hiv env plasmid 50 didrex it was found that igg, igm and iga responses were increased several folds, compared with naked dna it was also speculated that this formulation may 50 didrex also help protect the dna from nuclease degradation based on the evidence in the literature, the rationale for preparing nanoparticles rather than the more established microparticles 50 didrex is not necessarily clear with the dna formulations conclusions a number of systems with different types of antigen proteins, peptides, dna have been investigated with 50 didrex the particles ranging in size from nm to nm for most systems, the critical particle size is zm, with particles in the range of nm 50 didrex to zm, often inducing comparable immune responses in some cases, depending on the route of delivery, there may be increased immune responses with the smaller 50 didrex nanoparticles for in administration, there was no evidence that nm particles were better than micron particles for oral administration, some studies found enhanced responses with nanoparticles, 50 didrex compared with microparticles, while other studies found equivalence, or that microparticles elicited higher responses overall, the evidence for nanoparticles nm outperforming microparticles zm for enhanced 50 didrex immunogenicity is weak further examination is needed to support nanoparticles as a better formulation in place of microparticles also, some of the studies carried out were done model antigens and the same results maymay not apply to relevant antigens where vaccine efficacy is determined however, there are some advantages to nanoparticles 50 didrex compared with microparticles that have not been directly addressed for instance, smaller nanoparticles sub nm can be sterile filtered, allowing the particle preparation to be 50 didrex a nonsterile process with terminal sterilization the distinction between nanoparticles and microparticles is usually made by the authors and there is no consistency in what 50 didrex constitutes a nanoparticle, and this needs careful consideration when comparing results from the literature the important size measurement point is immediately prior to administration, post lyophilization, 50 didrex or other processing, and this is not always reported more relevant endpoints such as protective efficacy may be crucial in distinguishing between nanoparticles and microparticles nanoparticles and microparticles both constitute a very effective vaccine delivery system some of these formulations are currently in preclinical and clinical evaluations acknowledgments we would like to acknowledge the contributions of our colleagues in chiron corporation to the ideas contained in the chapter, particularly, all the members of the vaccine 50 didrex 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