Type III Hypersensitivity santos.pptx

8/14/2019 Type III Hypersensitivity santos.pptx

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Type III Hypersensitivity


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Type III HypersensitivityType III Hypersensitivity The formation of immune complexes through

the combination of antibody with antigen is the

first step in many immunological processes. One ofthe most significant of these processes is thecomplement cascade. When complement-activating immune complexes are deposited intissues, chemotactic factors are produced and leadto a local accumulation of neutrophils. These

neutrophils release their lysosomal emzymes andoxidizing radicals, and these in turn cause localtissue destruction. Lesions generated in thisfashion are called type III, or immune complex-mediated, hypersensitivity reaction.


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TYPE OF IMMUNE-COMPLEX DISEASETYPE OF IMMUNE-COMPLEX DISEASE

The combined effects of a low-grade persistentinfection and a weak antibody response lead to

chronic immune-complex formation, andeventual deposition of complexes in the tissues.


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Autoimmune disease Immune-complex disease is a frequent

complication of autoimmune disease, where the

continued production of autoantibody to a self-antigen leads to prolonged immune complexformation. As the number of complexes in the blood increases, the systems that are

responsible for the removal of complexes( mononuclear phagocyte, erythrocyte andcomplement) become overloaded, andcomplexes are deposited in the tissues.


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Inhalation of Antigenic Material Immune complexes may be formed at body

surfaces following exposure to extrinsic

antigens. Such reactions are seen in the lungsfollowing repeated inhalation of antigenicmaterials from moulds, plants and animals.


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Cause Antigen Site of complexdeposition

PersistentInfection

MicrobialAntigen

Infected organs,Kidney

Autoimmunity Self antigen Kidney, joint,arteries, skin

InhaledAntigen

Mould, plants oranimal antigen

Lung


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MECHANISM IN TYPE III HYPERSENSITIVITYMECHANISM IN TYPE III HYPERSENSITIVITY

Immune complexes are capable of triggering a wide variety ofinflammatory processes:

Complexes interact directly with basophils and platelets to induce the release of vasoactive amines.

Macrophages are stimulated to release cytokines, particularly TNFa

and IL-1, that are very important during inflammation.

They interact with the complement system to generate C3b and C5a

(anaphylatoxins). These complement fragments stimulate therelease of vasoactive amines (including histamine and 5-hydroxytryptamine) and chemotactic factors from mast cells andbasophils. C5a is also chemotactic for basophils, eosinophils, and

neutrophils.


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CLASSIFICATION OF TYPE III HYPRSENSITIVITY

The severity and significance of type IIIhypersensitivity reactions depend on the

amount and site of deposition of immunecomplexes.


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TWO MAJOR TYPE OF REACTION ARE RECOGNIZEDTWO MAJOR TYPE OF REACTION ARE RECOGNIZED

1. LOCAL TYPE HYPERSENSITIVITY REACTIONS(ARTHUS REACTION)

Named after the biologist who first described it. Thearthus reaction occurs when immune complexes aredeposited in tissues.


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Antigen injected intradermally orsubcutaneously combines withspecific antibody from the

blood to form immunecomplexes. The complexes acton platelets and mast cells,

which release vasoamines.Immune complexes alsoinduce macrophages to releaseTNF and IL-1. mast cell

products, including histaminesand leukotrienes, inducedincreased blood flow andcapillary permeability. Theinflammatory reaction ispotentiated by lysosomalenzymes released from thepolymorphs. The Arthusreaction can be seen inpatients with precipitatingantibodies, such as those withextrinsic allergic alveolitisassociated with Farmers lung

disease.


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2. GENERALIZED TYPE HYPERSENSITIVITY2. GENERALIZED TYPE HYPERSENSITIVITY When large amount of antigen enter the

bloodstream and bind to antibody, circulatingimmune complexes can form. If antigen is inaccess, small complexes form; because these arenot easily cleared by the phagocytic cells, theycan cause tissue-damaging type III reactions atvarious sites.


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Human diseases associated withType III hypersensitivity

vBacterial diseases Streptococcal

Mycoplasma pneomunia Leprosy SyphilisvViral diseases Infectious mononucleosis Hepatitis

Dengue hemorrhagicvParasitic diseases Malaria Leishmaniasis Schistosomiasis Onchocerciasis

vvTumors

vAutoimmune diseases Rheumatoid arthritis Systemic lupus

erythematosus Autoimmune thyroiditis

vOthers Serum sickness Hypersensitivity

pneumonitis IgA nephropathy

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Type III Hypersensitivity santos.pptx