Which cells in the thymus examine T cells for MHC

Question 1 of 5

Which cells in the thymus examine T cells for MHC restriction and tolerance of self during positive selection?

A. Medullary thymic epithelial cells B. Thymic dendritic cells C. Cortical thymic epithelial cells D. Bone marrow cells

Correct Answer: C

Rationale: Cortical thymic epithelial cells test T cells for MHC restriction in positive selection ; medullary cells handle negative selection.

Question 2 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 3 of 5

Dendritic cells in the skin, known as Langerhans cells, express very high levels of the NOD-like receptor, NLRP3. Previous studies showed that treatment of these cells with the Staphylococcus aureus pore-forming toxin causes Kâº efflux from the cells. The explanation for these results is:

A. NLRP3 is not activated by Kâº efflux from the cells B. The S. aureus toxin does not kill the Langerhans cells C. The live S. aureus bacteria activate a TLR and NLRP3 D. The S. aureus membrane prep does not contain a TLR ligand

Correct Answer: C

Rationale: Live S. aureus activates TLR and NLRP3 for IL-1; toxin alone (Kâº efflux) needs a second signal, membranes lack full stimuli.

Question 4 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 5 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.

Which cells in the thymus examine T cells for MHC restriction and tolerance of self during positive selection?

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