cell-mediated immunity

(redirected from Type IV Hypersensitivity)
Also found in: Dictionary, Thesaurus, Encyclopedia.

cell-·me·di·at·ed im·mu·ni·ty (CMI),

, cellular immunity
Immune responses mediated by activated, antigen-specific T lymphocytes. These T cells may function as effector cells or may orchestrate propagation of the inflammatory response and cellular recruitment through their secretion of cytokines and chemokines.
Synonym(s): delayed hypersensitivity (1)

cell-mediated immunity

n.
Immunity resulting from a cell-mediated immune response. Also called cellular immunity.

cell-me·di·at·ed im·mu·ni·ty

, cellular immunity (CMI) (sel'mē'dē-āt-ĕd i-myū'ni-tē, sel'yū-lăr)
Immune responses that are initiated by T lymphocytes and mediated by T lymphocytes, macrophages, or both (e.g., graft rejection, delayed-type hypersensitivity).
Enlarge picture
CELL-MEDIATED IMMUNITY

cell-mediated immunity

Abbreviation: CMI.
The regulatory and cytotoxic activities of T cells during the specific immune response. This process requires about 36 hr to reach its full effect. Synonym: T-cell–mediated immunity See: illustration; humoral immunity

Unlike B cells, T cells cannot recognize foreign antigens on their own. Foreign antigens are recognized by antigen-presenting cells (APCs) such as macrophages, which engulf them and display part of the antigens on the APC's surface next to a histocompatibility or “self-” antigen (macrophage processing). The presence of these two markers, plus the cytokine interleukin-1 (IL-1) secreted by the APCs activates CD4 helper T cells (TH cells), which regulate the activities of other cells involved in the immune response.

CMI includes direct lysis of target cells by cytotoxic T cells, creation of memory cells that trigger a rapid response when a foreign antigen is encountered for the second time, and delayed hypersensitivity to tissue and organ transplants. T cells also stimulate the activity of macrophages, B cells, and natural killer cells. These functions are controlled largely by the secretion of lymphokines such as the interleukins, interferons, and colony-stimulating factors. Lymphokines facilitate communication and proliferation of the cells in the immune system.

See also: immunity

cell-mediated immunity

Action by the immune system involving T cells (T LYMPHOCYTES) and concerned with protection against viruses, fungi, TUBERCULOSIS and cancers and rejection of foreign grafted material. Cell-mediated immunity is not primarily effected by ANTIBODIES.
References in periodicals archive ?
These materials can produce type IV hypersensitivity reactions.
Type IV hypersensitivity -- cell-mediated or delayed-type hypersensitivity -- is a T-cell mediated response.
An employee with Type IV hypersensitivity (contact allergic) who changes to low-protein, powder-free,[1] non-latex gloves will notice a remarkable difference, and offices that do so will greatly reduce exposure.
Because the cause in children is often due to exposure to certain plants, unsupervised time outdoors leading to a rash may lead parents to think of poison ivy or poison oak, which are type IV hypersensitivity reactions.
(1-3) Other hypotheses suggest that it may be a type IV hypersensitivity reaction.
A patch test relies on the principle of a type IV hypersensitivity reaction.