The design and use of submicrometre polymer particles that replicate and enhance the functions of mast-cell granules are reported online this week in Nature Materials. When used with the haemagglutinin antigen from influenza during vaccination, the synthetic granules enhance adaptive immune responses and increase the survival of mice after injection of a lethal dose of the H1N1 flu virus. Mast cells act to enhance immune responses through the release of insoluble granules that contain inflammatory mediators such as tumour necrosis factor (TNF). Inspired by mast-cell granules, Ashley St John and colleagues synthesized microparticles consisting of TNF entrapped in a matrix of the polysaccharide molecules, chitosan and heparin. When injected in mice, the particles travelled to draining lymph nodes, where they slowly released the encapsulated mediator and caused the activation of B-cell lymphocytes. The resulting enhanced adaptative immune responses were at levels comparable to or better than the standard vaccine adjuvant alum. The researchers also demonstrate that these particles offer greater flexibility in vaccine design, such as the ability to direct the character of the immune response towards Th1 lymphocytes.
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