Nokea
How does an antigen stimulate an immune response?
- A. It is captured, processed, and presented to a lymphocyte by a macrophage.
- B. It circulates in the blood, where it comes in contact with circulating lymphocytes.
- C. It is a foreign protein that has antigenic determinants different from those of the body.
- D. It combines with larger molecules that are capable of stimulating production of antibodies.
Correct Answer: A
Rationale: Antigens are captured, processed, and presented to lymphocytes by antigen-presenting cells like macrophages, initiating an immune response.
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Which of the following statements is incorrect about allergic reactions?
- A. They always require a sensitization step during which specific IgE are secreted
- B. Allergens causing hay fever are usually inhaled
- C. Food allergy can cause hives
- D. The current guidelines for preventing peanut allergy in infants is complete avoidance of peanuts and peanut-related products until at least six months of age
Correct Answer: D
Rationale: The correct answer is D because current guidelines actually recommend early introduction of peanuts to prevent peanut allergies, not complete avoidance. This is based on research showing early introduction can reduce the risk of developing peanut allergies. Choice A is correct as sensitization is a key step in allergic reactions. Choice B is correct as inhaled allergens can cause hay fever. Choice C is correct as food allergies can indeed manifest as hives.
Who introduced the concept of discrimination between self and non-self?
- A. Elie Metchnikoff
- B. Louis Pasteur
- C. Paul Ehrlich
- D. Charles Janeway
Correct Answer: C
Rationale: Paul Ehrlich introduced the concept of discrimination between self and non-self through his "horror autotoxicus" theory. He proposed that the immune system can differentiate between harmful non-self antigens and self-antigens. Ehrlich's theory laid the foundation for understanding immune responses and the development of immunology. Metchnikoff focused on phagocytosis, Pasteur on microbiology, and Janeway on innate immunity, not specifically on self vs. non-self discrimination.
The C3 convertase is
- A. An opsonin facilitating the phagocytic process
- B. Part of the Membrane Attack Complex (MAC) that leads to lysis of targets
- C. An enzyme able to cleave C3
- D. An inhibitor of C3b
Correct Answer: C
Rationale: The correct answer is C because the C3 convertase is an enzyme that cleaves C3 into C3a and C3b, an essential step in the complement cascade. This enzyme is crucial for the initiation of both the classical and alternative pathways. Choice A is incorrect as opsonins enhance phagocytosis but are not directly related to C3 convertase. Choice B is incorrect as the MAC is formed by the terminal complement components, not the C3 convertase. Choice D is incorrect as C3b is not an inhibitor but a product of C3 cleavage by the C3 convertase.
The adaptive immune response:
- A. Is dependent on the innate immune response for initiation
- B. Involves both humoral and cell-mediated responses
- C. Provides cytokines that influence the response of innate cells, i.e. macrophages
- D. All of the above
Correct Answer: D
Rationale: The correct answer is D because the adaptive immune response relies on the initiation by the innate immune response (A), involves both humoral (antibody production) and cell-mediated (T cell activation) responses (B), and produces cytokines that can modulate the activity of innate immune cells like macrophages (C). Therefore, all of the statements are true regarding the adaptive immune response, making option D the correct choice.
What is the main function of the Membrane Attack Complex (MAC)?
- A. Recruitment of neutrophils
- B. Phagocytosis activation
- C. Lysis of pathogens
- D. Enhancing cytokine production
Correct Answer: C
Rationale: The main function of the Membrane Attack Complex (MAC) is to lyse pathogens by creating pores in their cell membranes. First, MAC assembles on the pathogen's surface. Then, it forms a pore, disrupting the pathogen's membrane integrity, leading to cell lysis. This mechanism is crucial for the immune system to effectively eliminate pathogens.
Choice A (Recruitment of neutrophils) is incorrect because MAC is not involved in recruiting neutrophils. Neutrophil recruitment is typically mediated by other signaling molecules.
Choice B (Phagocytosis activation) is incorrect as MAC does not directly activate phagocytosis. Phagocytosis is a separate process involving the engulfment of pathogens by immune cells.
Choice D (Enhancing cytokine production) is incorrect because MAC does not directly enhance cytokine production. Cytokine production is mainly regulated by other immune cells and signaling pathways.