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Innate Immunity


adaptive immunity

immune response that is specific to a particular pathogen and arises after an immunizing event, such as vaccination or an infection

alternative pathway

complement pathway in which signal molecules bind to the surface of all cells. However, only host cells possess the cell surface proteins that prevent the signal cascade.


type of white blood cell that releases histamine and heparin to promote inflammatory reactions such as in allergic reactions, anaphylaxis, and asthma. Basophils make both histamine and serotonin.


movement of a cell in response to a chemical stimulus

classical pathway

complement pathway activated when complement signal proteins encounter an antibody bound to an antigen, which could be a potential pathogen or allergen

complement system

collection of immune system pathways and complement proteins that protect the body from microbes by enhancing the function of leukocytes and antibodies


one of a family of chemical messengers that regulate several different immune functions


shedding of the outermost layer of skin to protect the body from microbes bound to the skin


leukocyte that contains granules and releases cytotoxic chemicals to kill large parasites. It also aids in the regulation of allergies and asthma.


main method of oxygen delivery to the body


local response to injured tissue that results in an increased blood flow to the affected site and triggers a cell-mediated immune response if the second line of defense fails

innate immunity

nonspecific immune response, including chemical and physical barriers and internal cellular and chemical defenses


class of signaling proteins secreted by host cells when pathogens or cancerous cells are detected

lectin pathway

complement pathway activated when the signal protein mannan-binding lectin binds to mannose residues that are found on the surface of most organisms' cells but that are prominently displayed on pathogens


type of formed element in blood that aids the immune process and protects the body from infections and foreign invasion. Leukocytes lack hemoglobin and are therefore colorless, or "white," which is why they are also referred to as white blood cells.


one of a family of several different types of leukocytes, including B cells, T cells, and natural killer (NK) cells. Lymphocytes are found in lymphoid organs, such as lymph nodes.


organelle in the cytoplasm of eukaryotic cells containing degradative enzymes enclosed in a membrane


enzyme produced by many types of cells in the body that breaks down the bonds that make up bacterial cell walls

membrane attack complex (MAC)

aggregate of complement proteins C5–C9 that is formed in the membrane of a target cell and mediates cell lysis by formation of a membrane pore

mucosa-associated lymphoid tissue (MALT)

clusters of immune cells located in the mucous areas of the body (lungs, eyes, nasal passages) that protect the body from infection by pathogens


most common type of leukocyte in the body. It migrates from the bloodstream to carry out phagocytosis at the site of an injury.


molecules detected by the immune system that signal to immune cells the molecule may be an invading pathogen


coating the surface of an antigen with opsonins to enhance the interaction between phagocytic cells and the antigen

pattern recognition receptor

cellular receptor that binds specifically to molecules commonly associated with pathogens in order to signal infection to leukocytes in an innate immune reaction

Peyer's patch

small cluster of immune cells located along the wall of the small intestine that prevents infection by pathogens passing through the alimentary canal


process by which a leukocyte engulfs and destroys its target through a series of steps


molecules detected by the immune system that signal to immune cells the molecule is a part of the host body