A 34-year-old electric company worker comes to the physician with a skin rash on his right leg. He has not eaten any new foods or changed detergents, soaps, or lotions. On further questioning, the patient recalls that he recently worked on a repair job in an unmaintained, wooded area. He had atopic dermatitis as a child but no other significant illnesses. On physical examination, he appears uncomfortable and is constantly scratching his leg. His lungs are clear bilaterally and his heart sounds are normal. Examination of his right leg shows the findings in the image below. Which of the following cells is most responsible for causing the tissue damage seen in this patient?

Question

A 34-year-old electric company worker comes to the physician with a skin rash on his right leg.  He has not eaten any new foods or changed detergents, soaps, or lotions.  On further questioning, the patient recalls that he recently worked on a repair job in an unmaintained, wooded area.  He had atopic dermatitis as a child but no other significant illnesses.  On physical examination, he appears uncomfortable and is constantly scratching his leg.  His lungs are clear bilaterally and his heart sounds are normal.  Examination of his right leg shows the findings in the image below.  Which of the following cells is most responsible for causing the tissue damage seen in this patient?

Quizplus · Accepted Answer

11ec160b_37ad_53c0_9249_ed12bd2cca5a_MD0001_00 This patient's pruritic skin rash following wilderness exposure is consistent with poison ivy dermatitis, a form of contact dermatitis. Poison ivy, poison oak, and poison sumac all produce urushiol, a small allergenic substance that causes an immune response when attached to proteins (ie, a hapten). Following contact with these plants, patients develop a highly pruritic, erythematous rash consisting of papules, vesicles, and bullae that may show signs of excoriation. The rash most frequently affects exposed skin (eg, legs, forearms) and often forms linear streaks as the patient walks past the plant, dragging it along the skin. Contact dermatitis is a type IV (delayed-type) hypersensitivity reaction that occurs in 2 distinct phases: Depending on the etiologic agent, contact dermatitis can be mediated primarily by cytotoxic CD8+ T cells or CD4+ T_H1 cells (that cause indirect damage by activating macrophages). In urushiol-induced contact dermatitis, CD8+ T cells are the primary effector cells and directly destroy keratinocytes expressing haptenated proteins. (Choices A and C) Mast cells and basophils, along with IgE, are primarily responsible for type I hypersensitivity allergic reactions. Mast cells play a role in modulating the response in contact dermatitis by affecting antigen presentation and T-cell recruitment and activation, but they are not the main effector cells in type IV hypersensitivity. (Choice B) Eosinophils are cells that play a role in the defense against parasitic organisms and allergic reactions. (Choice D) Neutrophils are the primary phagocytic killers of the innate immune system and do not play a significant role in type IV hypersensitivity reactions. They are more important in type III hypersensitivity reactions, in which deposited immune complexes activate complement and cause neutrophil-mediated tissue damage. (Choice E) Plasma cells are the principal cells responsible for the synthesis of immunoglobulins, which are directly responsible for type II and III hypersensitivity reactions. Educational objective: Poison ivy dermatitis is a form of allergic contact dermatitis, which is a type IV hypersensitivity reaction mediated primarily by T lymphocytes. It manifests as intensely pruritic erythematous papules, vesicles, or bullae that often form linear patterns. __________ References: Contribution of CD4(+ )and CD8(+) T-cells in contact hypersensitivity and allergic contact dermatitis. (http://www.ncbi.nlm.nih.gov/pubmed/20477656) The role of CD4+ and CD8+ T cells in contact hypersensitivity and allergic contact dermatitis. (http://www.ncbi.nlm.nih.gov/pubmed/15246935) Allergic contact dermatitis. (http://www.ncbi.nlm.nih.gov/pubmed/15358566)

A 34-Year-Old Electric Company Worker Comes to the Physician with a Skin