Immune System/Disease Tracing

adaptive immunity

The kind of defense that is mediated by B lymphocytes (B cells) and T lymphocytes (T cells). It exhibits specificity, memory, and self-nonself recognition. Also called acquired immunity.

antibody

A protein secreted by plasma cells (differentiated B cells) that binds to a particular antigen and marks it for elimination.

antigen

a molecule that elicits an immune response

antigen presentation

The process by which an MHC molecule binds to a fragment of an intracellular protein antigen and carries it to the cell surface, where it is displayed and can be recognized by a T cell.

antigen receptor

The general term for a surface protein, located on B cells and T cells, that binds to antigens, initiating adaptive immune responses. The antigen receptors on B cells are called B cell receptors and the antigen receptors on T cells are called T cell receptors.

antigen-presenting cell

A cell that ingests bacteria and viruses and destroys them, generating peptide fragments that are bound by class II MHC molecules and subsequently displayed on the cell surface to helper T cells. Macrophages, dendritic cells, and B cells are the primary antigen-presenting cells.

apoptosis

Programmed cell death, in which a cell dies without lysis or release of contents

autoimmune disease

An immunological disorder in which the immune system turns against self.

B lymphocyte (B cell)

A type of lymphocyte that develops to maturity in the bone marrow. After encountering antigen, B cells differentiate into antibody-secreting plasma cells, the effector cells of humoral immunity.

CD4

A surface protein, present on most helper T cells, that binds to class II MHC molecules on antigen-presenting cells, enhancing the interaction between the T cell and the antigen-presenting cell.

CD8

A surface protein, present on most cytotoxic T cells, that binds to class I MHC molecules on target cells, enhancing the interaction between the T cell and the target cell.

cell-mediated immune response

The branch of acquired immunity that involves the activation of cytotoxic T cells, which defend against infected cells, cancer cells, and transplanted cells.

class I MHC molecules

A collection of cell surface proteins encoded by a family of genes called the major histocompatibility complex. Class I MHC molecules are found on nearly all nucleated cells.

class II MHC molecules

A collection of cell surface proteins encoded by a family of genes called the major histocompatibility complex. Class II MHC molecules are restricted to a few specialized cell cell types, commonly called antigen-presenting cells (dendritic cells, macrophages, and B cells).

clonal selection

The process by which an antigen selectively binds to and activates only those lymphocytes bearing receptors specific for the antigen. The selected lymphocytes proliferate and differentiate into a clone of effector cells and a clone of memory cells specific for the stimulating antigen. Clonal selection accounts for the specificity and memory of acquired immune responses.

complement system

A group of proteins that complement the antibodies and phagocytic cells; assists in ridding an organism of microbes and damaged cells; promotes inflammation.

cytokine

Any of a group of proteins secreted by a number of cell types, including macrophages and helper T cells, that regulate the function of lymphocytes and other cells of the immune system.

epitope

A small, accessible region of an antigen to which an antigen receptor or antibody binds; also called an antigenic determinant.

helper T cell

A type of T cell that, when activated, secretes cytokines that promote the response of B cells (humoral response) and cytotoxic T cells (cell-mediated response) to antigens.

histamine

A substance released by mast cells that causes blood vessels to dilate and become more permeable during an inflammatory response.

humoral immune response

The branch of acquired immunity that involves the activation of B cells and that leads to the production of antibodies, which defend against bacteria and viruses in body fluids.

immunization

The process of generating a state of immunity by artifical means. Active immunization: nonpathogenic version of a normally pathogenic microbe is administered, inducing B and T cell responses and immunological memory. Passive immunization: antibodies specific for a particular microbe are administered, conferring immediate but temporary protection.

immunoglobulin (Ig)

Any of the class of proteins that function as antibodies. Immunoglobulins are divided into five major classes that differ in their distribution in the body and antigen disposal activities.

inflammatory response

A localized innate immune defense triggered by physical injury or infection of tissue in which changes to nearby small blood vessels enhance the infiltration of white blood cells, antimicrobial proteins, and clotting elements that aid in tissue repair and destruction of invading pathogens; may also involve systemic effects such as fever and increased production of white blood cells.

innate immunity

The kind of defense that is mediated by phagocytic cells, antimicrobial proteins, the inflammatory response, physical barriers, and natural killer (NK) cells. It is present before exposure to pathogens and is effective from the time of birth.

lymphocyte

A type of white blood cell that mediates acquired immunity. Lymphocytes that complete their development in the bone marrow are called B cells, and those that mature in the thymus are called T cells.

macrophage

A phagocytic cell present in many tissues that functions in innate immunity by destroying microbes and in acquired immunity as an antigen-presenting cell.

major histocompatibility complex (MHC)

A family of genes that encode a large set of cell surface proteins called MHC molecules. Class I and class II MHC molecules function in antigen presentation to T cells. Foreign MHC molecules on transplanted tissue can trigger T cell responses that may lead to rejection of the transplant.

memory cell

One of a clone of long-lived lymphocytes, formed during the primary immune response, that remains in a lymphoid organ until activated by exposure to the same antigen that triggered its formation. Activated memory cells mount the secondary immune response.

natural killer (NK) cell

A type of white blood cell that can kill tumor cells and virus-infected cells; an important component of innate immunity.

neutrophil

The most abundant type of white blood cell. Neutrophils are phagocytic and tend to self-destruct as they destroy foreign invaders, limiting their life span to a few days.

passive immunity

Short-term immunity conferred by the administration of ready-made antibodies or the transfer of maternal antibodies to a fetus or nursing infant; lasts only a few weeks or months because the immune system has not been stimulated by antigens.

phagocytosis

A type of endocytosis involving large, particulate substances, accomplished mainly by macrophages, neutrophils, and dendritic cells.

plasma cell

The antibody-secreting effector cell of humoral immunity; arises from antigen-stimulated B cells.

primary immune response

The initial acquired immune response to an antigen, which appears after a lag of about 10 to 17 days.

secondary immune response

The acquired immune response elicited on second or subsequent exposures to a particular antigen. The secondary immune response is more rapid, of greater magnitude, and of longer duration than the primary immune response.

T cell receptor

the antigen receptor on T cells

T lymphocyte (T cell)

A type of lymphocyte, including the helper T cells and cytotoxic T cells, that develops to maturity in the thymus. After encountering antigen, T cells are responsible for cell-mediated immunity.

S in SIR model

Susceptible: Uninfected and unvaccinated individuals who can become infected

I in SIR model

Infectious: Individuals who are infected with a given pathogen and can pass the pathogen to susceptible individuals

R in SIR model

Removed: includes individuals who have been infected but have recovered, and are now immune (cannot be reinfected)

Individuals who are vaccinated and are now immune

recovery in SIR model

the process by which infected individuals recover (become removed)

transmission in SIR model

the process by which susceptible individuals become infected

contagious disease

an infectious disease that is easily spread through contact with other people (also called a communicable disease)

contact tracing

a public health strategy used to identify and monitor people who have been in close contact with someone who has tested positive for an infectious disease

infectious disease

A disease that is caused by a pathogen

noncommunicable disease

diseases are not transmitted through contact with an infected or afflicted person

communicable disease

a disease that can be spread from one organism to another (also known as a transmissible or contagious disease)

mast cell

Cells that release chemicals (such as histamine) that promote inflammation. A component of innate immunity.

natural killer cells

A type of white blood cell that can kill tumor cells and virus-infected cells; an important component of innate immunity.

dendritic cell

Antigen-presenting cells that process antigen material. Part of the innate immune system.

macrophages

phagocytize foreign substances and help activate T cells. Part of the innate immune system.