Untitled - D Ank Unlimited

delayed-type hypersensitivity (DTH) 219 delayed-type hypersensitivity (DTH)
Delayed-type hypersensitivity reaction. Mononuclear cells accumulate
around a blood vessel.
delayed-type hypersensitivity (DTH)
Cell-mediated immunity or hypersensitivity mediated by
sensitized CD4 T H1 lymphocytes. There is infiltration by T H1
cells, macrophages, and basophils, and granuloma formation.
Although originally described as a skin reaction that
requires 24 to 48 hours to develop following challenge with
antigen, current usage emphasizes the mechanism, which is
T cell-mediated, as opposed to placing an emphasis on the
temporal relationship of antigen injection and host response.
The CD4 + T lymphocyte is the principal cell that mediates
delayed-type hypersensitivity reactions. To induce a DTH reaction,
antigen is injected intradermally in a primed individual.
If the reaction is positive, an area of erythema and induration
develops 24 to 48 hours following antigen challenge. Edema
and infiltration by lymphocytes and macrophages occur at
the local site. The CD4 + T lymphocytes identify antigen on
Ia-positive macrophages and release lymphokines that entice
Schematic representation of type IV (cell-mediated) hypersensitivity. The upper frame illustrates tuberculin reactivity in the skin, which is mediated by
CD4 + helper/inducer T cells and represents a form of bacterial allergy. The lower frame illustrates the cytotoxic action of CD8 + T cells against a virusinfected
target cell that presents antigen via major histocompatibility complex (MHC) class I molecules to its T cell receptor (TCR), resulting in the
release of perforin and granzyme molecules leading to target cell lysis.
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