Type of immunologic injury in AIHA (Auto immune hemolytic anemia)

Ans. b (Type II) (Ref. Robbin's pathology 8th ed., Table no. 5-1; p. 121)Hypersensitivity Type IAnaphylactic and atopic - antigen cross-links IgE on presensitized mast cells and basophils, triggering release of vasoactive amines (i.e., histamine). Reaction develops rapidly after antigen exposure due to preformed antibody. E.g. include anaphylaxis, asthma, hives, local wheal and flare.First and Fast (anaphylaxis)Type I, II and Ml are all antibody mediated.Type IIAntibody mediated - IgM, IgG bind to antigen on "enemy" cell, leading to lysis (by complement) or phagocytosis.E.g. include autoimmune hemolytic anemia, Rh disease (erythroblastosis fetalis), Goodpasture's syndrome, rheumatic fever,Graves' disease, bullous pemphigoid, myasthenia gravis, ITP.Cy-2-toxicAntibody and complement lead to membrane attack complex (MAC).Type IIIImmune complex - antigen-antibody complexes activate complement, which attracts neurophils; neurophils release lysosomal enzymes.Examples include PAN, immune complex GN/PSGN, SLE, rheumatoid arthritis. Serum sickness - an immune complex disease (type III) in which antibodies to the foreign proteins are produced (takes 5 days).Immune complex form and are deposited in membranes where they fix complement (leads to tissue damage). More common than Arthus reaction. Arthus reaction - a local subacute antibody-mediated hypersensitivity (type Ml) reaction. Intradermal injection of antigen induces antibodies, which form antigen-antibody complexes in the skin. Characterised by edema, necrosis, and activation of complement. E.g. hypersensitivity pneumonitis (farmer's lung), thermophilic actinomycetes.Imagine an immune complex as 3 things stuck together; antigen-antibody- complement.Most serum sickness is now caused by drugs (not serum)Fever, urticaria, proteinuria, arthralgias, lymphadenopathy 5-10 days after antigen exposure. Antigen-antibody complexes cause the Arthus reaction.Type IVDelayed (T-cell mediated) type - sensitized T lymphocytes encounter antigen and then release lymphokines (leads to macrophage activation).4th and last - delayed. Cell mediated; therefore, it is not transferable by serum, e.g. 4 T's = T lymphocytes, Transplant rejection (GVHD),TB skin tests (PPD), Touching (contact dermatitis).Anaphylactic and AtopicType 1 Diabetes mellitusMultiple sclerosisGuillain-Barre syndromeHashimoto's thyroiditis