Type II-IV immunopathological
reactions
Type-II hypersensitivity
(cytotoxic)
• Mediated by IgG or IgM.
• Interaction between antigen and antibody leads to cell death, usually
mediated by the complement system or phagocytosis.
• The antigen may be autoantigen(so it includes antibody-mediated
autoimmune diseases) or may be of external origin (components of
microbes, drugs.. which attach to a cell membrane).
• Includes also post-transfusion hemolytic reactions.
• Also interactions between receptors and autoantibodies (leading to
receptor activation or blocade are involved in this group of
hypersensitivity reactions).
Anti-GBP antibodies
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Examples of antibody- mediated autoimmune diseases (type-II hypersensitivity)
Immunocomplex diseases
(type III immunopathological reaction)
• Caused by deposition of immune complexes in places different from their
normal metabolism.
• In case of circulating immune complexes (small, soluble complexes with
excess of antigen), they deposit mainly in blood vessels walls and
glomeruli leading to vasculitis and/or glomerulonephritis.
•
• Less frequent is the situation when immune complexes deposit in the
place of their formation (large complexes with excess of antibodies).
They deposit in the place of their formation. Extrinsic aleveolotis is the
best example.
• By activation of the complement system and phagocytioc cells they
induce local inflammation.
Diseases caused by immune complexes
deposition – laboratory tests
• In case of deposition of immunocomplexes in
vessel or glomeruli, the most important
laboratory test is the direct immunofluorescence
to detect the IgG part of the complexes.
• For diagnosis of extrinsic alveolitis, the presence
of IgG antibodies against suspicious antigen is
performed (immunodiffusion, ELISA in some
instances).
Type III hypersensitivity
Serum sickness
• Manifests 8-12 days after use of
xenogenic serum.
• Urticaria, fever, arthralgia,
lymphadenopathy
• Albuminuria
• Deposits of immunocomplexes in
vessels.
• Self-limiting disease, in case of need
steroids or antihistaminics can be used.
Serum Sickness
Extrinsic alveolitis
• Caused by deposition of insoluble immune
complexes in the lung tissue. The complexes
are formed from exogenous antigen and
excess of antibodies of IgG class.
• 6-8 hours after exposition the patient suffers
from dry cough, dyspnea, increased body
temperature, lymphadenopathy.
• Repeated expositions lead to lung fibrosis..
• Most frequently caused by bird antigens
(pigeons – pigeon breeder´s disease, parrots),
thermophil actinomycetes (farmers´s lungs
disease).
Patogenesis of extrinsic alveolitis
Type-IV hypersensitivity
• Mediated by T-lymphocytes, predominantly Th1
lymphocytes which consequently activate
macrophages – also called cellular or delayed
hypersensitivity.
• This reaction develops 1-2 days after exposure
– delayed type of hypersensitivity.
• Also autoimmunity caused by Tc lymphocytes is
included into this group of immunopathological
diseases.
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Mechanisms of T-cell mediated tissue injury (type-IV hypersensitivity)
Function of Th1 cells
Tuberculin reaction
Examples of diseases where type-IV
hypersensitivity plays a key role
• Contact exzema
• Cavitation in tuberculosis
• Sarcoidosis
• Several types of vasculitis
• Autoimmune diseases where Tlymphocytes
play a major role ( multiple
sclerosis)
Contact eczema
(contact dermatitis)
• Contact dermatitis is a red, itchy rash
caused by direct contact with a substance
as a type-IV allergic reaction to it.
• The reaction develops several days after
the exposure.
• Many substances can cause such
reactions, including soaps, cosmetics,
perfumes, metals (incl. jewelry), plants.
Contact dermatitis due to nickel hypersensitivity
Allergy Capital: Contact dermatitis. Australian Allergy, Asthma and Immunology Information.
http://www.allergycapital.com.au/allergycapital/Contact_dermatitis.html
Contact dermatitis
Skin patch test
• Is used for detection of type-IV hypersensitivity
(usually in the case of contact eczema).
• The antigen is included into an ointment.
• The ointment with the antigen is placed on the
skin and covered by an adhesive tape.
• After one day, the tape + the antigen are
washed.
• The results are read the next day.
• A positive reaction is an eczema-like exanthema
(red skin spots).
Patch tests
Wikipedia
Patch tests - results
https://www.researchgate.net/