pt with right arm pain after being stung by a bee. Physical

Discussion in 'USMLE STEP 1' started by Guest, Feb 24, 2011.

  1. Guest

    Guest Guest

    A 5-year-old child is brought in by his parents complaining of right arm pain after being stung by a bee. Physical exam reveals an edematous and eryttiematous plaque with evanescent borders and mild central pallor Otherwise the physical examination is not significant Which of the following is directs responsible for the findings observed in this patient?
    A Lysozyme
    B Histamine
    C. TNF-a
    D IL-2
    E CSb
  2. Guest

    Guest Guest

    histamine
  3. Guest

    Guest Guest

    Explanation:
    This child is expenencing a local allergic reaction (Type I trypersensitivity) to a sting from a honey bee. The cutaneous findings in this patient are consistent with a wheat a single lesion of urticana which is classically described as an erythematous papule or plaque with central pallor Upon initial exposure to allergens, a patient who will eventually develop an allergic response will undergo antibody class switching to IgE specific for allergens IgE produced by Blymphocytes and plasma cells binds to IgE ft receptors on basophils end mast cells. Reexposure to these bee venom allergens will result in cross-linking of IgE molecules on the surtace ot basophils and mast cells vith resultant degranulation and release of histamine (Choice B) proteases, heparin, leukotnenes and prostaglandins These agents increase local vascular permeability in reactions such as that described in the question stem, but they can also cause systemic vasodilatation, bronchocoristriction and inflammation leading to anaphylactic shock and potentially death.
    (Choice A) ysozne is an antimicrobial enzyme that can be found in many secretions Including tears and saliva as well as within granules in neutrophils. Lysozyme functions by hydrolyzing bonds in the peptidoglycan cell walls of bacterial organisms It plays no role in hypersensitivity reactions.
    (ChoIce C) TNFa is a cytokine produced by macrophages and mast cells It functions to signal for the apoptosis of tumor cells and activation of inflammatory cells such as CD4+ T-Pyrnphocytes, neutrophils. fibroblasts, endothelial cells and herriatopoietic stern cells. TNF-cc is elevated In many irdlarnmatory condiLions such as rheumatoid and psoriatic arthritis, and agents such as intliximab (Remicade) and etanercept (Enbrel) are humanized anti-TNF immunoglohulins that reduce inflammation in these conditions by binding TNF and thereby nor allowinq it to induce inflammation TNF may be elevated in Type IV (delayed type) hypersensitivity
    (Choice 0) lL-2 is a cytolone produced byT1-lyrnphocytes that signals for the proliferation and increased activity of TN and TC lymphocytes as well as NV cells TN1 cells are responsible for inducing a macrophage and cytotoxic Tlymphocyte-mediated iritlairrirriatory reaction. TN2 cells, on the oilier hand, induce humoral immunity, arid this pathway is signaled by IL-4
    (Choice E) CSb plays no role in causing hypersensitivity reactions directly, though it likely plays a role in Type Ill lrypersensibvity when circulating immune complexes fix complement against self antigens

    Educational Objective:
    the wheal observed after an insect sting results from an allergic, or Type I hypersensitivity reaction. The allergens present in tho insect venom rosult in antibody class switching to IgE on initial exposure, and subsequent exposure results in degranulanon of mast cells and basophils with release of histamine and hepann among other vacoactive mediators This degranulanon can cause a response as mild as an urticanal wtieal, or as severe as anaphylaxis.

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