Once the patient recovers from his acute illness, Candida antigen injection into his skin reveals no signs of inflammation after 48 hours. The same test performed in his mother produces 12 mm of skin induration within 48 hours. Which of the following cells are directly involved in the effector response observed in the mother?

Question

Once the patient recovers from his acute illness, Candida antigen injection into his skin reveals no signs of inflammation after 48 hours.  The same test performed in his mother produces 12 mm of skin induration within 48 hours.  Which of the following cells are directly involved in the effector response observed in the mother?

Quizplus · Accepted Answer

Intradermal injection of Candida antigens triggers a delayed type IV hypersensitivity reaction, which allows evaluation of the cell-mediated immune response. Injected Candida antigens are taken up by cutaneous antigen presenting cells (APCs), which display the antigens on major histocompatibility complex class II molecules to naïve CD4 cells. These cells are then induced to differentiate into type I helper (Th1) cells that secrete tumor necrosis factor and interferon-gamma, which recruit and activate macrophages. The macrophages phagocytose Candida antigens and secrete additional inflammatory mediators, producing a cutaneous inflammatory response that appears as an indurated wheal within 24-48 hours. Because exposure to Candida is ubiquitous, all healthy patients have memory T-cells against Candida. Failure to generate an appropriate cutaneous response indicates that the cell-mediated immune response is impaired (ie, T-cell anergy). Patients with SCID have T-cell dysfunction; therefore, they will show anergy in response to Candida challenge. (Choices A and B) B lymphocytes produce antibodies and are the main effectors of humoral immunity. Antibodies play a prominent role in type I (IgE-mediated), type II (eg, drug-induced hemolytic anemia), and type III (eg, serum sickness) hypersensitivity reactions (but not type IV reactions). (Choices C and E) Eosinophils and fibroblasts are not involved in type IV hypersensitivity reactions. Eosinophils are part of the innate immune system and are increased with atopic or parasitic diseases. Fibroblasts are found in connective tissue and are integral in wound healing through the production of extracellular matrix and collagen. Educational objective: The Candida antigen skin test assesses the activity of cell-mediated immunity because it requires an intact CD4 cell response. Failure to respond to candida antigen testing is typical in patients with severe combined immunodeficiency.

Once the Patient Recovers from His Acute Illness, Candida Antigen