The immune system has evolved to survey and respond appropriately to the universe of foreign pathogens, deploying an intricate repertoire of mechanisms that keep responses to host tissues in check. The immune system is typically divided into two categories--innate and adaptive. Innate immunity refers to nonspecific defense mechanisms that come into play immediately or within hours of an antigen's appearance in the body. Adaptive immunity refers to antigen-specific immune response. The antigen first must be processed and recognized, and then the adaptive immune system creates an army of immune cells specifically designed to attack that antigen. For the adaptive immune system, specificity and sensitivity are provided by a large repertoire of antigen T-cell receptors (TCRs) constructed in their extracellular domain to recognize antigenic peptide fragments restricted and presented by histocompatibility complex molecules, and coupled through intracellular domains to signal transduction modules that serve to transmit environmental cues inside the cell.
Inflammation is triggered when innate immune cells detect infection or tissue injury. Pattern recognition receptors (PRRs) respond to pathogen-associated molecular patterns (PAMPs) or host-derived damage-associated molecular patterns (DAMPs) by triggering activation of NF-κB, AP1, CREB, c/EBP, and IRF transcription factors. Induction of genes encoding enzymes, chemokines, cytokines, adhesion molecules, and regulators of the extracellular matrix promotes the recruitment and activation of leukocytes. Besides resolving infection and injury, chronic inflammation is a risk factor for cancer.
Immunity has a major impact on inflammatory diseases and cancer, and biologics targeting immune cells and their factors. Immunosuppressant drugs suppress, or reduce, the strength of the body’s immune system, and have been used in the treatment of organ transplantation or autoimmunine diseases. Immunomodulator drugs have contributed to the significant improvement against cancer and other related diseases.
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