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type IV cell-mediated hypersensitivity 728 typhoid vaccine
TSH
Stimulus
Anti-TSH-receptor
antibody
TSH receptor
Thyroid cell
Stimulus
Third form of type II hypersensitivity. Long-acting thyroid stimulator
(LATS), an IgG antibody specific for the thyroid-stimulating hormone
(TSH) receptor, leads to continuous stimulation of thyroid parenchymal
cells, causing hyperthyroidism. The IgG antibody mimics the action of
TSH.
Schematic
representation of the
formation and
deposition of immune
complexes in vessel
walls in type III
hypersensitivity
Formation of
microthrombi
Deposition of immune
complexes in vessel wall
Enzyme
release
Type III immune complex-mediated hypersensitivity.
Fc receptor
serum protein. When immune complexes are deposited
in tissues, complement is fixed and PMNs are attracted to
the site. Their lysosomal enzymes are released, resulting
in tissue injury. Localized immune complex disease,
sometimes called the Arthus reaction, is characterized by
acute immune complex vasculitis with fibrinoid necrosis
in the walls of small vessels.
type IV cell-mediated hypersensitivity
A form of hypersensitivity mediated by specifically
sensitized cells. Antibodies participate in type I, II, and
III reactions; T lymphocytes mediate type IV hypersensitivity.
Two types of reactions mediated by separate T cell
subsets are observed. Delayed-type hypersensitivity (DTH)
is mediated by CD4 + T cells, and cellular cytotoxicity is
mediated principally by CD8 + T cells. A classic delayed
hypersensitivity reaction is the tuberculin or Mantoux reaction.
Following exposure to Mycobacterium tuberculosis,
CD4 + lymphocytes recognize the antigens of the microbe
complexed with major histocompatibility complex (MHC)
class II molecules on the surfaces of antigen-presenting
cells that process the mycobacterial antigens. Memory T
cells develop and remain in the circulation for prolonged
periods. When tuberculin antigen is injected intradermally,
sensitized T cells react with the antigen on the surface of
the antigen-presenting cell, undergo transformation, and
secrete lymphokines that lead to manifestations of hypersensitivity.
Unlike antibody-mediated hypersensitivity,
lymphokines are not antigen-specific. In T-cell-mediated
cytotoxicity, CD8 + T lymphocytes kill antigen-bearing target
cells. Cytotoxic T lymphocytes play a significant role
in resistance to viral infections. MHC class I molecules
present viral antigens to CD8 + T lymphocytes as a viral
peptide–class I molecular complex that is transported to
the surfaces of infected cells. Cytotoxic CD8 + cells recognize
this action and lyse the target before the virus can
replicate, thereby stopping the infection.
typhoid vaccination
Refer to TAB vaccine.
typhoid vaccine
Following ingestion, virulent strains of Salmonella typhi
can penetrate the stomach acid barrier, colonize the intestinal
tract, pass through the lumen, and gain access to the
lymphatic system and bloodstream to produce disease. S.
typhi’s ability to induce disease and a protective immune
response depends on the presence of a complete lipopolysaccharide
in the microorganisms. Two forms of immunizing
preparation are currently in use. One is a live attenuated
S. typhi strain (Ty2la) used as an oral vaccine administered
in four doses to adults and children over 6 years of
age. It affords protection for 5 years. It is contraindicated
in patients taking antimicrobial drugs and patients with
acquired immune deficiency syndrome (AIDS). A second
type of the vaccine for parenteral use is prepared from the
capsular polysaccharide of S. typhi. It is administered to