Immune system is the body's defense mechanism against foreign organisms or substances and deviant native cells. It includes the humoral immune response and the cell-mediated response and consists of a complex of interrelated cellular, molecular, and genetic components. Diseases of the immune system are disorders caused by abnormal or absent immunologic mechanisms, whether humoral, cell-mediated, or both. (Description adapted from https://www.ncbi.nlm.nih.gov/mesh/68007154 and https://www.ncbi.nlm.nih.gov/mesh/68007107)