Which category of hypersensitivity involves complement activation?

Ans. C. 2 & 3Hypersensitivity reactions: (HSN)Type I: (Immediate/reaginic HSN).a. Antigen also k/a allergantb. Stimulates formation of IgE antibodies.c. Their subsequent binding to mast cell leads to manifestations of histamine release.d. E.g. Hay fever, Acute asthma, Urticaria, Theobald Smith phenomenon, Prausnitz Kustner reaction, Casoni's test, Schultz dale reaction.Type II: Cytotoxic HSNa. Cell bound antigenb. By IgG/IgMc. Activation of classical complement cascade leading to MAC formation and thereby cytotoxic killing.d. E.g. transfusion reactions, Erythroblastosis fetalis, ITP, good Pasteur Syndrome, Acute rheumatic fever.Type III: Immune complex HSNa. Antigen solubleb. Mediated by IgG/IgMc. Ag- Ab complex activates complement leading to destruction by neutrophils via release of lysosomal enzymes.d. E.g. SLE, Rheumatoid arthritis, HSP, PAN, infective endocarditis, Ac. Post Streptococcal glomerulonephritis, Schick test, Type 2 Lepra (ENL) reaction.Type IV: (Delayed HSN).a. No role of antibody.b. By stimulation of T- helper cell and Macrophage recruitment.c. E.g. Contact dermatitis, Lepromin test, Tuberculin test, Type I Lepra reaction, Fries test., Monte negro test.Type V:a. Cell bound antigenb. No activation of complementc. Binding with antibody causes cellular dysfunction leading to stimulation or inhibition.d. E.g. Grave's disease, Myasthenia gravis.