Erythroblastosis fetalis is which type of hypersensitivity: September 2007, 2009

Ans. B: Type II Type I hypersensitivity is also known as immediate or anaphylactic hypersensitivity. The reaction may involve skin (uicaria and eczema), eyes (conjunctivitis), nasopharynx (rhinorrhea, rhinitis), bronchopulmonary tissues (asthma) and gastrointestinal tract (gastroenteritis). The reaction usually takes 15 - 30 minutes from the time of exposure to the antigen, although sometimes it may have a delayed onset (10 - 12 hours). For example allergic asthma, hay fever etc. Immediate hypersensitivity is mediated by IgE. Type II hypersensitivity is also known as cytotoxic hypersensitivity and may affect a variety of organs and tissues. The antigens are normally endogenous, although exogenous chemicals (haptens) which can attach to cell membranes can also lead to type II hypersensitivity. Drug-induced hemolytic anemia, granulocytopenia and thrombocytopenia are such examples. Phagocytes and K cells may also play a role. The reaction time is minutes to hours. Type II hypersensitivity is primarily mediated by antibodies of the IgM or IgG classes and complement. Example include erythroblastosis fetalis, Goodpasture's nephritis Type III hypersensitivity is also known as immune complex hypersensitivity. The reaction may be general (e.g., serum sickness) or may involve individual organs including skin (e.g., systemic lupus erythematosus, Ahus reaction), kidneys (e.g., lupus nephritis), lungs (e.g., aspergillosis), blood vessels (e.g., polyaeritis), joints (e.g., rheumatoid ahritis) or other organs. This reaction may be the pathogenic mechanism of diseases caused by many microorganisms. Examples include SLE, farmer's lung disease Type IV hypersensitivity is also known as cell mediated or delayed type hypersensitivity. The classical example of this hypersensitivity is tuberculin (Montoux) reaction which peaks 48 hours after the injection of antigen (PPD or old tuberculin). The lesion is characterized by induration and erythema. Example includes tuberculin test, poison ivy, granuloma