Hypersensitivity

Type I hypersensitivity

IgE-mediated reactions leading to allergic responses.

Mechanism of Type I reactions

T helper 2 cells produce interleukin-4, activating B-cells to produce IgE, which causes mast cell degranulation.

Examples of Type I reactions

Allergic rhinitis, Asthma, Anaphylaxis.

Type II hypersensitivity

Tissue-specific reactions where the immune system attacks its own cells.

Mechanism of Type II reactions

Autoantibodies bind to altered self-antigens resulting in tissue destruction.

Examples of Type II reactions

Autoimmune hemolytic anemia, Heparin-induced thrombocytopenia, Graves disease, Myasthenia gravis.

Type III hypersensitivity

Immune complex-mediated reactions causing tissue damage.

Mechanism of Type III reactions

Antibodies form immune complexes with circulating antigens that activate complement leading to tissue destruction.

Examples of Type III reactions

Systemic lupus erythematosus, Raynaud phenomenon.

Type IV hypersensitivity

Cell-mediated reactions characterized by delayed hypersensitivity.

Mechanism of Type IV reactions

T helper 1 cells produce interferon gamma, activating macrophages and T-cytotoxic cells.

Examples of Type IV reactions

Contact sensitivity to poison ivy and latex, Mycobacterial infection, TB.