Nokea
What is the role of perforin released by NK cells?
- A. Activating B cells
- B. Forming pores in target cell membranes
- C. Engulfing pathogens
- D. Inducing inflammation
Correct Answer: B
Rationale: Perforin released by NK cells forms pores in target cell membranes, allowing for the entry of granzymes which induce target cell death. This process is crucial for the immune response against infected or abnormal cells. Activating B cells (A) is not the role of perforin, as B cells are primarily activated by antigens. Engulfing pathogens (C) is the role of phagocytes like macrophages, not perforin. Inducing inflammation (D) is not directly related to the function of perforin in forming pores in target cell membranes.
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Which enzyme catalyzes the addition of deoxynucleotides to the 3'OH ends of DNA molecules?
- A. Phosphohydrolase
- B. T4 DNA ligase
- C. Terminal deoxynucleotidyl transferase
- D. DNA endonuclease
Correct Answer: C
Rationale: The correct answer is C: Terminal deoxynucleotidyl transferase (TdT). TdT catalyzes the addition of deoxynucleotides to the 3'OH ends of DNA molecules. It does so by adding nucleotides in a template-independent manner, making it crucial for generating diversity in immune cell receptor genes.
A: Phosphohydrolase - This enzyme is not involved in adding deoxynucleotides to DNA ends.
B: T4 DNA ligase - This enzyme catalyzes the joining of DNA fragments, not the addition of deoxynucleotides.
D: DNA endonuclease - This enzyme cleaves DNA internally, not involved in adding deoxynucleotides to DNA ends.
What is hypersensitivity in immunology?
- A. An excessive or inappropriate immune response causing tissue damage
- B. The body's inability to mount an immune response
- C. A low-level immune reaction to antigens
- D. A mechanism for faster immune response during infections
Correct Answer: A
Rationale: Step-by-step rationale:
1. Hypersensitivity in immunology refers to an exaggerated or inappropriate immune response.
2. This excessive response can lead to tissue damage and various immune-mediated conditions.
3. Choice A accurately describes this concept.
Summary:
- Choice A is correct as it accurately defines hypersensitivity.
- Choice B is incorrect as hypersensitivity involves an exaggerated immune response, not an inability to mount one.
- Choice C is incorrect as hypersensitivity is not a low-level immune reaction.
- Choice D is incorrect as hypersensitivity is not a mechanism for faster immune response, but rather an overreaction.
Before the patient receives a kidney transplant, a crossmatch test is ordered. What does a positive crossmatch indicate?
- A. Matches tissue types for a successful transplantation
- B. Determines paternity and predicts risk for certain diseases
- C. Establishes racial background and predicts risk for certain diseases
- D. Cytotoxic antibodies to the donor contraindicate transplanting this donor’s organ
Correct Answer: D
Rationale: A positive crossmatch indicates the presence of preformed cytotoxic antibodies against the donor, contraindicating transplantation.
Which of the following is NOT true about a potential vaccine that induces a strong cytotoxic T cell response to influenza virus but failed to induce neutralizing antibodies:
- A. It would not prevent actual infection
- B. It would lessen the severity of disease
- C. It may be more cross-protective against different variants of influenza virus
- D. It would result in failure to clear the virus
Correct Answer: D
Rationale: The correct answer is D because a strong cytotoxic T cell response can still effectively clear the virus even without neutralizing antibodies. Cytotoxic T cells directly kill infected cells, helping to control and eliminate the virus. Therefore, the vaccine would not result in failure to clear the virus.
A) Incorrect: While the vaccine may not prevent infection, the presence of cytotoxic T cells would help in controlling and reducing the severity of the infection.
B) Incorrect: The vaccine may indeed lessen the severity of the disease by aiding in the clearance of infected cells.
C) Incorrect: A strong T cell response can provide broader protection against different variants of the virus.
When a B cell undergoes class switching it allows the cell to:
- A. Differentiate into a memory cell
- B. Make two or more antibody classes at the same time
- C. Stop making one class of antibody and begin to make another
- D. Receive costimulatory signals from any T helper cell subset
Correct Answer: C
Rationale: Rationale:
1. Class switching in B cells involves changing the class of antibody produced.
2. This allows the B cell to stop making one class of antibody and start making another.
3. This process enhances the immune response by generating antibodies with different functions.
4. Differentiating into a memory cell (choice A) is a separate process from class switching.
5. Making two or more antibody classes simultaneously (choice B) is not a characteristic of class switching.
6. Costimulatory signals from T helper cells (choice D) are important for B cell activation but not directly related to class switching.