Nokea
The differentiation of activated Th cells into various effector subsets depends mostly on:
- A. Signal 1 of activation
- B. The influence of polarizing cytokines secreted by dendritic cells
- C. Whether the T cell expresses CD4 or CD8
- D. The duration of signaling induced by TCR binding to peptide-MHC
Correct Answer: B
Rationale: The correct answer is B because polarizing cytokines secreted by dendritic cells play a crucial role in determining the differentiation of activated Th cells into specific effector subsets. These cytokines guide the Th cells towards different functional phenotypes, such as Th1, Th2, Th17, or Treg cells. This process helps tailor the immune response to the specific type of pathogen encountered. Choices A, C, and D are incorrect because while signal 1 of activation, T cell receptor co-receptors, and duration of signaling are important factors in T cell activation and differentiation, they do not have as direct and significant an impact on effector subset differentiation as the influence of polarizing cytokines.
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All of the following are true with respect to IgM antibodies EXCEPT which one
- A. they fix complement
- B. they occur on the surface of lymphocytes
- C. they predominate in the primary response to antigen
- D. mediate allergic reactions
Correct Answer: D
Rationale: The correct answer is D. IgM antibodies do not mediate allergic reactions. IgE antibodies are responsible for allergic reactions. IgM antibodies fix complement, occur on the surface of lymphocytes, and predominate in the primary response to antigens. IgM is the first antibody produced in response to an infection, playing a key role in the activation of the complement system. IgM antibodies are mainly found in the blood and lymphatic system, not on the surface of lymphocytes. IgE antibodies are the primary mediators of allergic reactions by triggering the release of histamine and other inflammatory molecules.
Which of the following would provide an individual with passive immunity to 'Pathogen X'?
- A. Inoculation with a vaccine against Pathogen X
- B. Infection with Pathogen X
- C. Transfer to the individual of serum from someone who has survived an infection with Pathogen X
- D. Living amongst others who have been immunized against Pathogen X
Correct Answer: C
Rationale: The correct answer is C, transfer of serum from someone who has survived an infection with Pathogen X. This provides passive immunity through the transfer of antibodies from the immune individual to the recipient, offering immediate protection. Choice A involves active immunity through vaccination, which requires the individual's immune response to produce antibodies. Choice B involves active infection, not passive immunity. Choice D mentions living amongst immunized individuals, which may confer herd immunity but does not provide passive immunity on an individual level.
What are the two main outcomes of clonal selection?
- A. T cell activation and cytokine suppression
- B. Differentiation into effector and memory cells
- C. Pathogen destruction and tissue repair
- D. Phagocytosis and complement activation
Correct Answer: B
Rationale: The correct answer is B: Differentiation into effector and memory cells. During clonal selection, activated lymphocytes undergo differentiation into effector cells that combat the current infection and memory cells that provide long-lasting immunity. Effector cells directly eliminate pathogens, while memory cells remember the specific pathogen for future encounters. Choices A, C, and D are incorrect as they do not accurately represent the main outcomes of clonal selection. T cell activation and cytokine suppression (A) are processes involved in immune response regulation rather than the direct outcomes of clonal selection. Pathogen destruction and tissue repair (C) are broader immune responses that occur after clonal selection. Phagocytosis and complement activation (D) involve innate immune responses, not the adaptive immune responses seen in clonal selection.
Which of the following statements is incorrect?
- A. BLASTX searches protein databases
- B. BLASTX use translated nucleotide as the query sequence
- C. Both TBLASTX and TBLASTN translate query into 6 reading frames
- D. BLASTN searches protein databases
Correct Answer: D
Rationale: The correct answer is D because BLASTN searches nucleotide databases, not protein databases. BLASTN uses a nucleotide sequence as the query to find similar sequences in nucleotide databases. This is different from BLASTX, which searches protein databases using translated nucleotide sequences (answer A is correct). TBLASTX and TBLASTN translate the query sequence into six reading frames to search for similarities in both nucleotide and protein databases (answer C is correct). BLASTN is specifically designed for nucleotide sequence searches, making statement D incorrect.
The Ig class found in breast milk is
- A. IgA
- B. IgM
- C. IgD
- D. IgG
Correct Answer: A
Rationale: The correct answer is A: IgA. IgA is found in breast milk and plays a crucial role in providing immunity to the infant. It helps protect against infections in the digestive and respiratory tracts. IgM is primarily found in the bloodstream, IgD is mainly on the surface of B cells, and IgG is transferred from the mother to the fetus during pregnancy. IgA is the specific immunoglobulin class present in breast milk, making it the correct choice.