Nokea
The clonal selection theory explains:
- A. That one given lymphocyte expresses multiple antigen receptors with different specificity
- B. That antigens influence the generation of antigen receptors during lymphocyte development
- C. How the immune response to an antigen increases the number of lymphocytes specific for that antigen
- D. The increase in blood neutrophils observed during bacterial infections
Correct Answer: C
Rationale: Rationale:
1. Clonal selection theory states that specific lymphocytes are activated by antigens.
2. Upon activation, these lymphocytes proliferate to form a clone of cells specific to the antigen.
3. This increases the number of lymphocytes specific for the antigen.
4. Choice C correctly aligns with the essence of clonal selection theory.
Summary:
A: Incorrect - Clonal selection theory does not involve a single lymphocyte expressing multiple antigen receptors.
B: Incorrect - Antigens do not influence the generation of antigen receptors, but rather activate specific lymphocytes.
D: Incorrect - Clonal selection theory focuses on lymphocyte response to antigens, not neutrophil increase during infections.
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Which of the following is necessary to produce a T-cell repertoire capable of interacting with self MHC molecules?
- A. Two of these responses are correct
- B. Positive selection
- C. Negative selection
- D. Induction of energy
Correct Answer: B
Rationale: Positive selection is necessary to produce a T-cell repertoire capable of interacting with self MHC molecules. During positive selection in the thymus, T-cells that can recognize self MHC molecules are retained, ensuring self-tolerance and functionality. Negative selection eliminates self-reactive T-cells. Induction of anergy is a state of T-cell unresponsiveness and does not contribute to the development of a functional T-cell repertoire. Choice A is incorrect as only positive selection is necessary for self MHC recognition.
Which compounds produced by microorganisms can cause fever in humans and can withstand autoclaving?
- A. endotoxin
- B. Lipid A
- C. lipopolysaccharide
- D. peptidoglycan
Correct Answer: D
Rationale: The correct answer is D, peptidoglycan. Peptidoglycan is a component of bacterial cell walls that can trigger fever in humans. It is a sturdy molecule that can withstand autoclaving.
A: Endotoxin is a component of the outer membrane of Gram-negative bacteria, not resistant to autoclaving.
B: Lipid A is the toxic component of endotoxin, not resistant to autoclaving.
C: Lipopolysaccharide is the major component of the outer membrane of Gram-negative bacteria, not resistant to autoclaving.
What is the primary function of cytokines in the immune system?
- A. To act as a physical barrier to pathogens
- B. To orchestrate and drive immune responses
- C. To destroy red blood cells
- D. To generate antibodies
Correct Answer: B
Rationale: The correct answer is B: To orchestrate and drive immune responses. Cytokines are signaling molecules that coordinate various aspects of the immune response, such as inflammation, cell proliferation, and differentiation. They regulate communication between immune cells to mount an effective defense against pathogens.
A: To act as a physical barrier to pathogens - Incorrect. Physical barriers include skin and mucous membranes, not cytokines.
C: To destroy red blood cells - Incorrect. Cytokines are not involved in destroying red blood cells.
D: To generate antibodies - Incorrect. While cytokines can influence antibody production, their primary role is not in generating antibodies.
What is the main limitation of innate immunity compared to adaptive immunity?
- A. It cannot produce cytokines
- B. It lacks memory and specificity
- C. It does not include physical barriers
- D. It cannot activate complement
Correct Answer: B
Rationale: The main limitation of innate immunity compared to adaptive immunity is that innate immunity lacks memory and specificity. This means that innate immune responses do not improve upon repeated exposure to the same pathogen and cannot target specific antigens efficiently. Adaptive immunity, on the other hand, can remember previous encounters with pathogens and mount targeted responses. Choices A, C, and D are incorrect because innate immunity can produce cytokines, includes physical barriers like skin and mucous membranes, and can activate complement as part of its defense mechanisms.
Which of the following is a clinical feature of Grave's disease?
- A. Pulmonary fibrosis
- B. Exophthalmos and goiter
- C. Skin vasculitis
- D. Eczematous reaction
Correct Answer: B
Rationale: The correct answer is B: Exophthalmos and goiter. In Grave's disease, there is an overproduction of thyroid hormones leading to hyperthyroidism. Exophthalmos (bulging eyes) and goiter (enlarged thyroid gland) are classic clinical features due to autoimmune stimulation of thyroid-stimulating hormone receptors. Pulmonary fibrosis (A) is not typically associated with Grave's disease. Skin vasculitis (C) and eczematous reaction (D) are also not commonly seen in Grave's disease.