- Active immunity: immunity provided by the body producing its own antibodies against a particular antigen; results from exposure to the antigen via infection or vaccine
- AIDS: acquired immune deficiency syndrome; the late stages of HIV infection
- Allergy: abnormal immune system sensitivity to an otherwise harmless antigen
- Antibody: protein in blood plasma that attaches to a particular antigen
- Antigen: foreign molecule that provokes an immune response
- Autoimmune disease: disorder in which the immune system attacks the body's own molecules
- B cell: lymphocyte that matures in the bone marrow and later produces antibodies; responsible for humoral immunity
- Cell-mediated immunity: type of immunity produced by T cells that attack infected or abnormal body cells
- Cytotoxic T cell: lymphocyte that attacks body cells infected with pathogens
- Helper T cell: lymphocyte that activates cytotoxic T cells and stimulates B cells to produce antibodies
- Histamine: chemical alarm signal released by mast cells that causes blood vessels to dilate during an inflammatory response
- HIV (human immunodeficiency virus): virus that destroys helper T cells and causes AIDS
- Humoral Immunity: specific immunity produced by B cells that produce antibodies that circulate in body fluids
- Immunity: Resistance to a specific pathogen
- Infectious disease: A disease caused by a pathogen
- Inflammatory response: nonspecific defense against infection, characterized by redness, heat, swelling, and pain
- Interferon: protein produced by cells in response to being infected by a virus; helps other cells resist the virus
- Memory Cell: long-lasting lymphocyte formed during the primary immune response that is reactivated on exposure to the same pathogen, quickly producing many clones
- Nonspecific defense: physical or chemical barrier that prevents pathogens from entering the body
- Passive immunity: resistance to a particular pathogen that results when the body acquires antibodies for it, as when a baby receives antibodies from its mother
- Pathogen: A disease causing organism or virus
- Plasma cell: antibody-secreting B cell
- T cell: lymphocyte that matures in the thymus; is responsible for cell-mediated immunity and also plays a role in humoral immunity
- Vaccine: dose of a disabled or destroyed pathogen (or part of a pathogen) used to stimulate a long-term immune defense against the pathogen