<prompt> Serum sickness is which type of hypersensitivity reaction?Type IType IIType IIIType IV  <response>: Ans. c Type III. Textbook of Microbiology by Ananthnarayan, 6th ed., 155HYPERSENSITIVITY ReactionsTypeMechanismE.g.Hints to rememeberType IAnaphylactic and AtopicAntigen 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 anaphylaxisType I, II, and III are all antibody mediated.Type II Cytotoxicantibody mediatedAntibody mediatedIgM, IgG bind to antigen on enemy cell, leading to lysis by complement or phagocytosis.- Autoimmune Hemolytic anemia,- Rh disease,- Good pastures syndrome,- Rheumatic fever,- Graves 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 IVDelayedcell mediatedDelayed T cell mediated type - sensitized T lymphocytes encounter antigen and then release lymphokines leads to able by macrophage activation.- 4Ts -- T lymphocytes,- Transplant reactions,- TB skin tests,- Touching contact dermatitis. Hypersensitivity pneumonitis farmers lung by Thermophilic actinomycetes...as per Harrisons 17th ed.4th and last - delayed. 