An infant with recurrent bacterial and fungal infe

Question 1 of 5

An infant with recurrent bacterial and fungal infections is suspected to have an immunodeficiency disease. Within two days after exposure to a pathogen, the organisms have proliferated to dangerous levels requiring immediate systemic antibiotic treatment. It is unlikely that this infant has a defect in B or T lymphocyte responses to the infection because:

A. Bacteria and fungi do not require B cell or T cell responses for their clearance B. Bacteria and fungi are not efficiently transported to draining lymph nodes to initiate adaptive immune responses C. Systemic infections of bacteria and fungi are usually cleared by the spleen D. The defective immune response occurs too rapidly following infection to be due to a defect in B or T lymphocytes responses

Correct Answer: D

Rationale: Adaptive responses (B/T cells) take days, so rapid failure suggests innate defects; bacteria/fungi need adaptive immunity , transport occurs , spleen aids but isn't sole .

Question 2 of 5

Some viruses have mechanisms to down-regulate MHC class I protein expression on the surface of cells in which the virus is replicating. This immune evasion strategy might prevent effector CD8 cytotoxic T cells from recognizing and killing the virus-infected cells. Would this immune evasion strategy also prevent the initial activation of virus-specific CD8 T cells?

A. Yes, because no viral peptide:MHC class I complexes would form to activate CD8 T cells B. No, because dendritic cells would take up infected cells and cross-present viral peptides to activate CD8 T cells C. No, because some presentation of MHC class I complexes with viral peptides would occur before the virus could down-regulate all the surface MHC class I protein D. Yes, because this immune evasion strategy would also function in dendritic cells, even if the virus doesn't replicate in dendritic cells

Correct Answer: B

Rationale: DCs cross-present viral peptides , bypassing evasion; not all cells (A, D) or early presentation explain activation.

Question 3 of 5

Vibrations from the sound waves are amplified by

A. the eardrum B. Anvi C. Stirrup D. All above

Correct Answer: C

Rationale: The stirrup (stapes) in the middle ear amplifies sound vibrations, while the eardrum transmits and the anvil (incus) transfers them, but amplification is primarily by the stapes.

Question 4 of 5

Which of the following statements regarding antigens and antibodies is false?

A. An antibody usually recognizes and binds to an antigenic determinant B. A single antigen may stimulate the immune system to make several distinct antibodies to it C. Most antigens are proteins or large polysaccharides on the surfaces of viruses or foreign cells D. Each antibody has only one antigen-binding site

Correct Answer: D

Rationale: Antibodies have two antigen-binding sites, not one, making D false; the others are true about antigen-antibody interactions.

Question 5 of 5

Which of the following compounds is produced and secreted by mast cells during an allergic reaction?

A. interferon B. allergens C. histamine D. perforin

Correct Answer: C

Rationale: Mast cells release histamine in allergic reactions, causing symptoms like swelling, not interferon, allergens (triggers), or perforin.

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