Hypersensitivity-type 3

Immune Complex-Mediated (Type III) Hypersensitivity:

Antigen combines with antibody within the circulation (circulating immune complexes) , and these are deposited.

Antigen-antibody complexes produce tissue damage by eliciting inflammation at sites of deposition.

Two types of antigens cause immune complex-mediated injury:

(1) exogenous antigens: such as foreign protein, bacterium, or virus.(microbial proteins) (2) endogenous antigens: individual can produce antibody against self-components such as nucleoproteins.

IMMUNE COMPLEXESLarger complexes

activate complement in the blood and are

phagocytosed by macrophages.

These moderate complexes are deposited

in the basement membranes of blood vessels and tissues.

Here they cause inflammation of target

tissue/organ through the attraction of leucocytes leading to anaphylactic

shock.

Mechanism Of Tissue Injury Immune complexes trigger inflammatory processes:

activate release1) Immune complexes the complement

anaphylatoxins C3a, C5a

stimulate release

degranulation of basophiles and mast cells histamine

Histamine vascular permeability and help deposition of immune complexes

2) Neutrophils are attracted to the site by immune complexes and release lysosomal enzymes which damage tissues and intensify the inflammation

process.

Examples of Immune Complex-Mediated Diseases: [ diseases and antigens ]

Systemic lupus erythematosus : DNA, and nucleoproteins antigens.Polyarteritis nodosa : Hepatitis B virus surface

antigenPoststreptococcal glomerulonephritis :

Streptococcal cell wall antigen. Acute glomerulonephritis : Bacterial antigens

(Treponema); parasite antigens (malaria, schistosomes); and tumor antigens.

Reactive arthritis : Bacterial antigens (Yersinia).

Immune complex-mediated diseases can be: generalized (systemic) ; or localized .

Systemic Immune Complex Disease: Acute serum sickness: Once complexes

are deposited in tissues, they initiate an acute inflammatory reaction (approximately 10 days after antigen administration), clinical features such as fever, urticaria, arthralgias, lymph node enlargement, and proteinuria appear. Local Immune Complex Disease :

Arthus reaction: a localized area of tissue necrosis resulting from acute immune complex vasculitis, usually elicited in skin.

ARTHUS REACTIONLocal inflammatory reaction with NecrosisFew hours after Ag inoculationInoculated Animal is previously immunized by

same Ag immunized animal has titers of precipitating

IgG Abs Arthus lesions evolve over a few hours and

reach a peak 4 to 10 hrs after injection When injection site develops visible edema

with severe hemorrhage occasionally followed by ulceration

General hypersensitivity e.g.

serum toxicity.

Specific Reactions like kidney lupus

nephritis,Joints

rheumatoid arthritis.

Anaphylaxis

Non human

proteins given

therapeuticaly bind to

IgG.

These complexes get deposited in the

alveoli of the lungs.

Inflammation leads to anaphyl

axis.