TYPE II HYPERSENSITIVITY
Introduction
- Antibody mediated/Cytotoxic Hypersensitivity
- Depends on the abnormal production of IgG or IgM directed against tissue antigens
- or a normal reaction to foreign antigens expressed on host cells.
- Mediated by antibodies directed toward antigen on cell surfaces.
Peak action time
- 15-30mins
Three different antibody-dependent mechanisms :
Opsonization and complement and Fc receptor-mediated phagocytosis
- Most common
- Antibodies are deposited on the surface of cells leads to :Activation of complement and generation of C3b
- Enhanced phagocytosis through Fc receptor and phagocytes (opsonization)
- C3b also acts as opsonin.
- It enhances phagocytosis through C3b receptor on phagocytes (opsonization).
- Example →Transfusion reactions, Erythroblastosis fetalis
Complement and Fc receptor mediated inflammation
- Injury is due to inflammation.
- Antibodies deposit in extracellular tissues Deposited antibodies activate complement
- basement membrane
- matrix
- Generate by-products such as C5a
- C5a acts as chemokine for neutrophil and monocyte.
- Which bind to deposited antibody via Fc receptors
- Get activated.
- Examples → Glomerulonephritis, vascular rejection in organ grafts.
Antibody mediated cellular dysfunction
- Antibodies directed against cell surface receptors .
- Examples: Graves disease and Myasthenia gravis
The type V reactions
- Antibody mediated destruction of cells
- By antibody dependent cellular cytotoxicity (ADCC).
- ADCCThe type V reactions are sometimes considered as a subtype of the type II hypersensitivity.
- Kills cells that are coated with low doses of Ig G antibody
- Cell lysis proceeds without phagocytosis
- Example: membranous glomerulonephritis seen in SLE
Examples Of Type II Hypersensitivity:
- Transfusion reactions
- Erythoblastosis fetalis (Hemolytic disease of neontates)
- All hemolytic anemia or agraulocytosis or thrombocytopenia
- Pemphigus syndrome
- Bullous pemphigoid
- Pernicious anemia
- Thrombotic phenomenon
- Acute rheumatic fever
- Some forms of vasculitides and certain drug reactions.
- Phagocytosis of tumor cells or parasite .
- Some role in graft rejection
- Thyrotoxicosis / Grave’s disesas
- Myasthenia gravis
Exam Important
Introduction
- Antibody mediated/Cytotoxic Hypersensitivity
- Depends on the abnormal production of IgG or IgM directed against tissue antigens
Three different antibody-dependent mechanisms :
Opsonization and complement and Fc receptor-mediated phagocytosis
- Most common
- Example →Transfusion reactions, Erythroblastosis fetalis
Complement and Fc receptor mediated inflammation
- Examples → Glomerulonephritis, vascular rejection in organ grafts.
Antibody mediated cellular dysfunction
- Antibodies directed against cell surface receptors .
- Examples: Graves disease and Myasthenia gravis
The type V reactions
- By antibody dependent cellular cytotoxicity (ADCC).
- The type V reactions are sometimes considered as a subtype of the type II hypersensitivity.
- Example: membranous glomerulonephritis seen in SLE
Examples
- Transfusion reactions
- Erythoblastosis fetalis (Hemolytic disease of neontates)
- All hemolytic anemia or agraulocytosis or thrombocytopenia
- Pemphigus syndrome
- Bullous pemphigoid
- Pernicious anemia
- Thrombotic phenomenon
- Acute rheumatic fever
- Some forms of vasculitides and certain drug reactions.
- Phagocytosis of tumor cells or parasite .
- Some role in graft rejection
- Thyrotoxicosis / Grave’s disesas
- Myasthenia gravis
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