What is the purpose of negative selection in the t

Question 1 of 5

What is the purpose of negative selection in the thymus?

A. To train T cells to attack foreign cells only B. To train T cells to recognize self MHC molecules and not attack our own body cells C. To train T cells to recognize self MHC molecules and attack our own body cells D. To train B cells to produce antibodies against foreign antigens

Correct Answer: B

Rationale: Negative selection eliminates self-reactive T cells ; it refines tolerance, not just foreign attack , not self-attack , not B cells .

Question 2 of 5

The best evidence supporting the concept of immunological memory is:

A. The increased numbers of antigen receptors expressed by lymphocytes after primary exposure to an antigen B. The increased levels of cytokines made by lymphocytes after primary exposure to an antigen C. The increased rapidity and magnitude of the secondary response to the same antigen D. The increased swelling of lymph nodes during the secondary response to the same antigen

Correct Answer: C

Rationale: Memory is evidenced by faster, stronger secondary responses ; receptor numbers , cytokines , or swelling are less direct indicators.

Question 3 of 5

In recent years, several new vaccines have been developed that are made from purified viral surface proteins, rather than intact or live viruses. They are referred to as subunit vaccines. In order to generate a protective adaptive immune response to a subunit vaccine, the viral protein(s) must be mixed with an adjuvant. The adjuvant functions to:

A. Mimic the process of normal virus entry by binding to the host receptor and inducing receptor-mediated endocytosis B. Induce vascular permeability to promote the accumulation of fluid and serum proteins at the vaccine injection site C. Induce the production of chemotactic proteins that recruit neutrophils and then monocytes to the site of vaccine injection D. Stimulate dendritic cells to up-regulate co-stimulatory molecules and migrate to the regional lymph node

Correct Answer: D

Rationale: Adjuvants activate DCs for co-stimulation and lymph node migration ; not entry , permeability , or just chemotaxis .

Question 4 of 5

Empty MHC class I and MHC class II molecules are rapidly removed from the cell surface. This process prevents:

A. The accumulation of empty MHC molecules on the cell surface which would interfere with T cells recognizing pathogen-derived peptide:MHC complexes B. Pathogens from evading the immune response by inducing peptide release from cell surface MHC molecules C. MHC class I molecules from being internalized into endosomes and binding endosome-derived peptides D. HLA-DM from trafficking to the cell surface with MHC class II

Correct Answer: A

Rationale: Empty MHC removal ensures pathogen peptide presentation; not evasion , endosomal binding , or HLA-DM .

Question 5 of 5

The human retina contains rods and cone which are able to

A. convert the photo power to the chemical power B. absorption of ultraviolet C. convert photo power to electrical form and send action potentials to the brain D. absorption of infrared

Correct Answer: C

Rationale: Rods and cones convert light (photo power) into electrical signals (action potentials) sent to the brain, not chemical power or UV/infrared absorption.

What is the purpose of negative selection in the thymus?

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