Adaptive Immunity


active immunity

immune response that is specific to a particular pathogen and arises after an immunizing event

adaptive immunity

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


type of protein that can be secreted from or bound to the surface of B cells and recognize antigens


a specific portion of a foreign particle that activates an immune response

antigen binding site

a constant domain and the variable region that binds to a target antigen


antibody that can neutralize a specific toxin

B cell

adaptive immune cell that reaches maturation in the bone marrow

cell-mediated immunity

immune reaction that utilizes the ability of T cells to kill other cells without the involvement of antibodies

class switch recombination

capacity to change a specific part of each antibody molecule to replace the mu chain that forms the IgM antibody with a delta (D), alpha (A), gamma (G), or epsilon (E) chain to form each other antibody type

clonal selection

process that kills autoreactive immune cells, those that can induce an immune response against a person's own body and organs


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


small molecule that can induce an immune response when it is attached to a larger carrier molecule

humoral immunity

immune response mediated by antibodies circulating throughout the body

immune memory

ability to deliver long-lasting, protective immunity against a pathogen

immune tolerance

state of unresponsiveness to something that should elicit an immune response


ability of a person to have a normal immune response when challenged by a pathogen


condition of immune system that is suppressed or inactive

killer T cell

T cell capable of destroying other cells

major histocompatibility complex (MHC)

set of proteins that presents antigens on the surface of cells to support recognition by antigen receptors

major histocompatibility complex I (MHC I)

set of proteins found on all nucleated cell types that are derived from intracellular proteins and present antigens on the cell’s surface, which are recognized by CD8+ T cells

major histocompatibility complex II (MHC II)

set of proteins only found on antigen-presenting cells, such as dendritic cells, macrophages, and B cells, and is used by these cells to present antigens picked up from extracellular sources, such as other dying cells or proteins secreted from other cells, which are recognized by CD4+ T cells

naive B cells and T cells

B cells and T cells that are mature, but have not yet been exposed to an antigen and can not generate an immune response


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

passive immunity

immunity that results from the transfer of antibodies from one person to another

secondary response

immune response that occurs any time a pathogen is encountered subsequent to an initial infection that prompted the development of memory cells against the pathogen’s antigen


ability of an adaptive immune cell to recognize a particular target antigen

T cell

adaptive immune cell that is generated in the bone marrow and matures in the thymus

T cell clone

a T cell in a population of effector T cells that are specific to a particular antigen


nonpathogenic substance that is used to generate a protective immune response against a particular disease

variable region

part of the B cell antigen receptor protein that determines what antigen it can bind