Ans. c (Type III). (Textbook of Microbiology by Ananthnarayan, 6th ed., 155)HYPERSENSITIVITY ReactionsTypeMechanismE.g.Hints to rememeberType I(Anaphylactic and Atopic)Antigen cross -links IgE on presensitized mast cells and basophils, causing of vasoactive amines (i.e., histamine) release.- Anaphylaxis,- Asthma,- Hives- Local wheal and flareFirst and fast (anaphylaxis)Type I, II, and III are all antibody mediated.Type II Cytotoxic(antibody mediated)Antibody mediatedIgM, IgG bind to antigen on "enemy" cell, leading to lysis (by complement) or phagocytosis.- Autoimmune Hemolytic anemia,- Rh disease,- Good pasture's syndrome,- Rheumatic fever,- Grave's disease,- Bullous pemphigoid,- Myasthenia gravis,- ITP.Cy-2-toxic.Antibody and complement lead to membrane attack complex (MAC).Type IIIC-ComplementImmune complexImmune complex-- activate complement, which attracts neutrophils; neutrophils release lysosomal enzymes,- PAN,. Immune complex GN, SLE, rheumatoid arthritis.- Serum sickness--antibodies to the foreign proteins are produced (takes 5 days). Immune complexes form and are deposited in membranes, where they fix complement (leads to tissue damage).More common than Arthus reaction.- Arthus reaction--fntraderma! Injection of antigen induces antibodies, which from antigen-antibody complexes in the skin, causing edema, necrosis and activation of complement.Imagine an immune complex as 3 things stuck together; antigen antibody- complementType IVDelayed(cell mediated)Delayed (T cell mediated) type - sensitized T lymphocytes encounter antigen and then release lymphokines (leads to able by macrophage activation).- 4T's -- T lymphocytes,- Transplant reactions,- TB skin tests,- Touching (contact dermatitis). Hypersensitivity pneumonitis (farmer's lung) by Thermophilic actinomycetes....as per Harrison's 17th ed.4th and last - delayed.