Immunologic adjuvants: An overview of Toll-like receptors mechanism of action in triggering the immune responses

Cytokines play a crucial role in controlling the immune system, and their signals direct the immune response towards either an antibody-mediated or a cell-mediated immunity. These molecules trigger the innate and adaptive immune responses including maturation of antigen presenting cells, differentiation of Th1 and Th2 cells, and induction of natural killer cells and cytotoxic T lymphocytes. Therefore, cytokines could be promising vaccine adjuvants for enhancing the immune response against infectious agents. Dendritic cells are responsible for antigen uptake and presentation to T cells and represent a key target for adjuvant activity. Many proteins are involved in regulating and maintaining homeostasis of the immune system. TLR family of proteins capable of producing cytokines including interferon type I and proinflammatory cytokines lead to express genes involved in immune system function. These proteins are the key regulator of interferon production in fibroblasts and specialized dendritic cells and their role as an adjuvant in the improvement of immune responses is evaluated. In this article, the structure and function of these receptors in triggering immune responses with rely upon their signaling pathways are reviewed