Zika Virus Infection: Virology & Control by Abubakar Yaro

Author:Abubakar Yaro [Yaro, Abubakar]
Language: eng
Format: epub
Published: 2016-04-01T06:00:00+00:00

Adjuvants for vaccines: Vaccines are designed with emphasis on specific, tailored formulations with the aim of eliciting precise and potent immunological responses. An important component of a vaccine is the adjuvant which is a molecule or compound that ensures robust immune response to the co-formulated antigens. A number of mechanisms that underlies the activities of adjuvants have been described which had led to the optimization of adjuvants. Recognition of PAMPs by the immune system is achieved through the various PRRs, the most notably been TLRs. TLR act as sensors for different damage-associated molecular pattern (DMAP) or danger signals which are generated by TLR-agonists such as dsRNA, DNA, and glycolipids found on the surface of most pathogens. The ligand of the pathogens bind to these receptors thereby creating diverse immune responses that are the basis for multiple adjuvants currently in used / or development. Adjuvants enhances and/ or modulates immune response by exposing antigens to APC and at the same time conferring immune activation signals. Few adjuvants have been approved for use in human vaccines, and they mainly act by stimulating humoral immunity. There is therefore the need to develop safe and effective adjuvant system that can stimulate CMI. Adjuvants can be grouped in delivery systems or immunostimulators. The delivery systems which serves as carriers of the antigen and immunostimulators in the vaccines are mostly particles, e.g. liposome, emulsion droplets, and immune-stimulating complexes (ISCOMs). Liposome was used as vaccine adjuvant around 1974 and it was reported that immunization of mice with diphtheria toxoid (DT) adjuvanted with phospholipid based liposome resulted in increased antibody titers in comparison to immunization with non-adjuvanted DT. Since then the use of liposomes as vaccine adjuvant has been a subject of intense research. Liposome mechanism of action as adjuvant involves their ability to interact with APCs to enhance the exposure of antigen and immunostimulators to APCs. When using liposomes as adjuvants, they act as delivery system. As a result of their versatility, it possible to incorporate different types of molecules into the same liposome dispersion such as lipid-based immunostimulators and a protein-based antigen. A number of studies have elucidated the effect of adjuvants on vaccine. Most vaccine contain aluminum adjuvant but their exact mechanism of action is unclear. Shi et al proposed that aluminum adjuvants may enhance immune activation by binding and recognizing lipids that are key component of lipid rafts. Antunez et al also proposed lipid-mediated mechanism of action for aluminum adjuvant. As stated earlier there are urgent need to develop new adjuvants. Lee et al proposed synthetic hemozoin (sHZ), a chemical analog to hemozoin which is produced by malaria parasite. It exhibited potent adjuvant effect which enhanced antigen-specific immune response to vaccines. The potency of sHZ as adjuvant is not only limited to malaria specific vaccine but also shown to be effective in influenza and dog allergy models. The adjuvants to be used for vaccine should be safe. For example cholera toxin (CT) is one of the most powerful known mucosal adjuvant but is toxic for human use.

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