Nokea
The most abundant class of immunoglobulin in serum is
- A. IgE
- B. IgA
- C. IgD
- D. IgG
Correct Answer: D
Rationale: The correct answer is D: IgG. IgG is the most abundant class of immunoglobulin in serum, constituting about 75% of total immunoglobulins. IgG plays a crucial role in humoral immunity, providing long-term protection against pathogens. IgE (A) is involved in allergic responses, IgA (B) is mainly found in mucosal secretions, and IgD (C) functions as a cell surface receptor on B cells. IgG is the primary immunoglobulin responsible for secondary immune responses and provides the bulk of the adaptive immune response.
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Select the property that applies only to pathogens:
- A. Replicate in (or on) a host
- B. Infect host cells
- C. Cause disease in a host with normal immune functions
- D. Are transmitted between individuals of a given species
Correct Answer: C
Rationale: The correct answer is C because pathogens are microorganisms that specifically cause disease in a host with normal immune functions. Pathogens have mechanisms to evade or overcome the host's immune system, leading to the development of diseases. Choices A and B are characteristics of both pathogens and non-pathogenic organisms. Choice D is incorrect because not all pathogens are transmitted between individuals of the same species; some pathogens can be transmitted from animals to humans or through environmental sources.
Terminal deoxynucleotidyl transferase catalyzed reactions produce fragments with
- A. poly A or poly C tails
- B. poly C tails
- C. poly A tails
- D. poly A or poly T tail
Correct Answer: A
Rationale: Terminal deoxynucleotidyl transferase (TdT) adds nucleotides to the 3' end of DNA fragments in a template-independent manner. This results in the production of fragments with poly A or poly C tails. TdT does not add poly T tails, making option D incorrect. It also does not specifically add only poly C tails (option B) or poly A tails (option C). The addition of poly A or poly C tails by TdT is essential for techniques like DNA sequencing and PCR, where these tails are utilized for downstream applications.
What is the role of complement component C3b in immune responses?
- A. Initiates MAC formation
- B. Acts as an opsonin to enhance phagocytosis
- C. Triggers inflammation
- D. Neutralizes cytokines
Correct Answer: B
Rationale: The correct answer is B: C3b acts as an opsonin to enhance phagocytosis. C3b binds to pathogens and enhances their recognition by phagocytic cells, facilitating their engulfment and destruction. This process is crucial for efficient immune responses. A, MAC formation, is initiated by the membrane attack complex, not C3b. C, inflammation, is triggered by various mediators such as histamine and cytokines, not C3b. D, neutralizing cytokines, is not a function of C3b; cytokines are regulatory proteins involved in immune responses.
Which characteristic describes immunoglobulin E (select all that apply)?
- A. Assists in parasitic infections
- B. Responsible for allergic reactions
- C. Present on the lymphocyte surface
- D. Protects body surfaces and mucous membranes
Correct Answer: A
Rationale: IgE is involved in defense against parasites and is responsible for triggering allergic reactions by binding to mast cells and basophils.
The percentage of developing thymocytes undergoing negative selection in the thymus is close to
- A. 90%
- B. 50%
- C. 25%
- D. 10%
Correct Answer: A
Rationale: The correct answer is A (90%). Negative selection in the thymus eliminates self-reactive T cells. The process ensures self-tolerance. The majority of developing thymocytes are removed during negative selection, making it close to 90%. Choices B, C, and D are incorrect because negative selection eliminates a high percentage of thymocytes, not a lower percentage as indicated in those options.