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59. The correct answer is E. This is a case of rheumatic fever, which is an immunologically mediated sequela to Streptococcus pyogenes pharyngitis. It is a type II cytotoxic hypersensitivity, involving antibodies that bind to cardiac tissue, activate complement, and thereby cause cell destruction. It is therefore most similar to idiopathic thrombocytopenic purpura, which is also a form of type II cytotoxic hypersensitivity, in this case mediated by antibodies against platelets producing complement fixation and causing the clotting dyscrasia.

Atopic allergy (choice A) is a form of type I hypersensitivity, mediated by IgE antibodies and basophils and mast cells.

Contact dermatitis (choice B) is a form of type IV hypersensitivity mediated by T cells and macrophages.

Graft-vs-host disease (choice C) is a form of type IV hypersensitivity mediated by T cells and macrophages.

Graves disease (choice D) is a form of type II hypersensitivity, but it is NOT cytotoxic in its action. Instead, antibodies to the TSH receptors on thyroid cells cause overstimulation of the gland and its eventual exhaustion.

Myasthenia gravis (choice F) is a form of type II hypersensitivity, but NOT of the cytotoxic variety. In this case, antibodies to the acetylcholine receptors on neurons diminish neurotransmission.

Rheumatoid arthritis (choice G) is a form of type III hypersensitivity, caused by immune complex deposition in joints and subsequent activation of complement.

Serum sickness (choice H) is a form of type III hypersensitivity, caused by immune complex deposition.

Systemic lupus erythematosus (choice I) is a form of type III hypersensitivity, caused by immune complex deposition.


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