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The MMR (Measles, MUMPs, Rubella) vaccine has been the object of controversy after a report (lately declared fraudulent) of an association with development of:
- A. Multiple sclerosis
- B. Autism
- C. Encephalitis
- D. Epilepsy
Correct Answer: B
Rationale: The correct answer is B: Autism. The controversy surrounding the MMR vaccine and autism emerged from a fraudulent report that falsely claimed a link between the two. Numerous scientific studies have since debunked this association, confirming the safety of the MMR vaccine. Autism is a neurodevelopmental disorder with a complex etiology, involving genetic and environmental factors, but not vaccines. Choices A, C, and D are incorrect as there is no proven causal link between the MMR vaccine and multiple sclerosis, encephalitis, or epilepsy.
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Which of the following is a feature of antigen recognition by B cells?
- A. Their antigen receptors are never secreted
- B. Their antigen receptors recognize a fragment of protein in combination with an MHC molecule
- C. Their receptors each have two identical antigen binding sites
- D. They recognize pattern associated molecular structures (PAMPs) that are unique to a particular pathogen
Correct Answer: C
Rationale: The correct answer is C because B cell receptors, known as antibodies, are Y-shaped proteins with two identical antigen-binding sites. This feature allows B cells to bind to specific antigens with high specificity. Each B cell receptor can bind to a unique antigen, leading to the initiation of an immune response.
Choice A is incorrect because B cell receptors can be secreted as antibodies to target antigens outside the cell.
Choice B is incorrect because B cell receptors recognize antigens directly, not in combination with MHC molecules.
Choice D is incorrect because B cells primarily recognize specific antigens rather than general PAMPs associated with pathogens.
What role do cytokines play in innate immunity?
- A. They directly kill pathogens
- B. They act as signaling molecules to coordinate immune responses
- C. They only function in adaptive immunity
- D. They inhibit phagocytosis
Correct Answer: B
Rationale: The correct answer is B because cytokines act as signaling molecules to coordinate immune responses in innate immunity. They help regulate inflammation, activate immune cells, and promote clearance of pathogens. Option A is incorrect because cytokines do not directly kill pathogens. Option C is incorrect as cytokines play a crucial role in both innate and adaptive immunity. Option D is incorrect because cytokines do not inhibit phagocytosis; instead, they enhance this process to help eliminate pathogens.
Which of the following sentences concerned with lymph node structure is incorrect?
- A. naïve B lymphocytes are found in the cortex
- B. naïve T lymphocytes are found in the paracortex
- C. naïve lymphocytes enter the lymph node through the efferent lymphatic vessel
- D. Antigens can enter the lymph node through afferent lymphatic vessels
Correct Answer: C
Rationale: Rationale:
C is incorrect because naïve lymphocytes actually enter the lymph node through the afferent lymphatic vessel, not the efferent. A carries lymphocytes into the lymph node, and D is true since antigens enter through afferent vessels. B is correct, as naïve T cells are found in the paracortex.
The earliest event of an inflammatory response is
- A. Release of chemokines
- B. Recruitment of neutrophils
- C. Activation of adaptive immunity
- D. Activation of TLRs
Correct Answer: D
Rationale: The correct answer is D: Activation of TLRs. The earliest event in an inflammatory response is the activation of Toll-like receptors (TLRs) by recognizing pathogen-associated molecular patterns (PAMPs). This triggers a signaling cascade leading to the release of pro-inflammatory cytokines and chemokines, which then recruit neutrophils to the site of infection. Activation of adaptive immunity (choice C) occurs later in the immune response, as it involves the activation of T and B cells. While chemokines (choice A) are involved in recruiting immune cells, their release is a consequence of TLR activation. Neutrophils (choice B) are recruited after the release of chemokines.
The reason for using Taq polymerase for PCR is that
- A. it has regions that are complementary to primers.
- B. only minute amounts are needed for each cycle of PCR
- C. it binds more readily than other polymerases to primer.
- D. it is heat stable and can withstand the temperature changes of the cycler.
Correct Answer: D
Rationale: The correct answer is D because Taq polymerase is heat-stable, allowing it to withstand the high temperatures used in PCR cycles without denaturing. This heat stability is crucial for the repeated heating and cooling cycles in PCR. Choice A is incorrect because Taq polymerase does not need to be complementary to primers. Choice B is incorrect because the amount needed is not the main reason for using Taq polymerase. Choice C is incorrect because binding affinity to primers is not the primary reason for using Taq polymerase.