Ans: Type Hypersensitivity reaction is also known as tissue-specific, cytotoxic or cyolytic hypersensitivity reaction. It is characterized by antibodies that attack antigens on the surface of specific cells or tissues. The reaction is organ specific. This antigen-antibody reaction is immediate, occurring within 15 to 30 minutes after exposure to the antigen. IgG and IgM are the principal antibodies. It is mediated by the complement system and a variety of principal effector cells, including tissue macrophages, platelets, killer cells, neutrophils, and eosinophils. The symptoms are related to the antigenic target of the antibody. Examples of the hypersensitivity reaction include ABO transfusion reactions, hemolytic disease of the newborn, MG, throiditis, hyperacute graft rejections, and autoimmune hemolytic anemias.
Type III hypersensitivity reaction is also known as immune complex or Arthus disease. This reaction is a sequential process beginning with an interaction between a soluble antigen and soluble antibody. It is characterized by antigen-antibody complex formation that usually occurs in the circulation. The complex is then deposited into vascular walls or extravascular tissues, causing an inflammatory reaction. The reaction is not organ specific and peaks 6 hours after exposure to the antigen. IgG is the principal antibody. The principal effector cells include neutrophils and mast cells. Examples of this type of hypersensitivity reaction include serum sickness, glomerulonephritis, systemic lupus erythematosus, rheumatoid arthritis, drug-induced vasculitis, and polyarteritis nodosa.