The immune system is an intricate network of molecules, cells, tissues, and organs that work together to defend the body against infectious agents and malignant cells. It is broadly divided into innate and adaptive branches, which are both essential for efficient host defense. The innate immune response is immediately available, but is not specific for any one pathogen. Innate immune cells such as natural killer (NK) cells, neutrophils, monocytes/macrophages and dendritic cells (DCs) express pathogen recognition receptors (PRRs) that recognize pathogenassociated molecular patterns (PAMPs), such as the bacterial cell wall component lipopolysaccharide (LPS). The interaction between PRR and PAMPs activates cells of the innate immune system to engulf pathogenic microbes and to secrete cytokines and chemokines, resulting in the induction of an inflammatory response and mobilization of immune cells into the site of infection. In addition, DCs and monocytes process and present peptides derived from foreign antigens bound to specialized molecules called major histocompatibility complex (MHC) molecules on their cell surface to naïve T lymphocytes thereby activating them and initiating the adaptive immune response (Janeway 2008).
