Why are MHC II molecules necessary for antigen pre

Question 1 of 5

Why are MHC II molecules necessary for antigen presentation by APCs?

A. Because T cells only recognize presented antigens B. Because MHC II presents small fragments of proteins C. Because many pathogens reproduce in tissues or blood D. All of the above

Correct Answer: D

Rationale: MHC II is essential as T cells recognize peptide-MHC complexes , it presents fragments , and pathogens are extracellular ; all apply .

Question 2 of 5

Select the statement that is true about the spleen

A. The spleen filters the lymph much the same way the lymph nodes filter the blood B. The spleen harbors eosinophils waiting for parasites to attack the body C. The spleen is the major site of red and white blood cell production in the adult D. The spleen filters the blood much the same way the lymph nodes filter the lymph

Correct Answer: D

Rationale: The spleen filters blood, not lymph ; lymph nodes filter lymph (A reversed), eosinophils aren't spleen-specific, and adult blood production is in bone marrow.

Question 3 of 5

Given the enormous heterogeneity of antigen receptors expressed on the populations of naive B and T lymphocytes, the adaptive immune response relies on a process whereby the rare lymphocyte that binds to the antigen is first induced to proliferate, before it can perform its effector function. For B cells, there is a clever mechanism that ensures that the specificity of the antibody secreted by the plasma cell will recognize the same pathogen that initially stimulated the B cell antigen receptor and induced B cell proliferation. This mechanism is:

A. Naive B cells express a single BCR, secreting the same antibody as plasma cells B. The naive B cell expresses a single specificity of B cell antigen receptor, and then up-regulates the expression of this receptor so it can bind tightly to the pathogen C. The plasma cell proliferates after it has finished secreting antibody to generate more plasma cells with specificity for the pathogen D. The plasma cell traps secreted antibody molecules in its extracellular matrix and uses these antibodies to bind to the pathogen

Correct Answer: A

Rationale: Naive B cells express a single BCR, secreting the same antibody as plasma cells ; multiple receptors , upregulation , or post-secretion proliferation don't occur.

Question 4 of 5

B cells express a complement receptor that binds to C3b cleavage products, such as iC3b and C3dg. When a B cell with an antigen receptor that specifically recognizes that pathogen also has its complement receptor stimulated because the pathogen is opsonized with these C3 fragments, B cell activation is greatly enhanced. This mechanism functions to:

A. Ensure that pathogens are readily detected by the adaptive immune system before they replicate to high levels in the host B. Prevent B cells from being activated in response to antigens that are not pathogens C. Allow B cells to phagocytose the pathogen and help destroy it D. Induce increased rounds of B cell replication to make more pathogen-specific B cells

Correct Answer: A

Rationale: Complement enhances B-cell detection of pathogens early ; not prevention , phagocytosis , or just replication .

Question 5 of 5

Antibodies that bind with high affinity to some viral surface proteins require heavy chain CDR3 loops of unusual length. Whereas the average human heavy chain CDR3 length is ~15 amino acids, antibodies with V_H CDR3 loops of >30 amino acids are readily detected in the repertoire. These antibody heavy chains with CDR3 lengths of >30 amino acids would likely be missing in individuals lacking:

A. RAG-1 and RAG-2 B. DNA-dependent protein kinase (DNA-PK) C. The nuclease, Artemis D. TdT

Correct Answer: D

Rationale: TdT adds nucleotides for long CDR3; RAG , DNA-PK , Artemis , and Ku are recombination essentials.

Why are MHC II molecules necessary for antigen presentation by APCs?

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