A substance which is recognized as foreign by the immune system. Antigens are either whole microorganisms, or they can be part of an organism or virus. These are a specific type of leukocytes which are mononuclear. They are a critical part of immune response because they provide the specificity and memory which is needed for long-term immunity. The two main types of lymphocytes are T cells and B cells.
Cytokines are chemical substances that are secreted by lymphocytes, monocytes and macrophages.
T cells mediate cellular reactions. These are the essential conductors of the immune system, and turn on antibody production. A type of T cell which kill cells that are infected by viruses or cancer. They are also known as T8 cells. A subset of T cells which is responsible for turning off the immune response.