Nokea
The activation of naïve T cells takes place in:
- A. Germinal centers
- B. Primary lymphoid tissues
- C. Secondary lymphoid tissues
- D. None of the above
Correct Answer: C
Rationale: The correct answer is C: Secondary lymphoid tissues. Naïve T cells are activated in secondary lymphoid tissues such as lymph nodes and spleen. These tissues are where T cells encounter antigen-presenting cells, receive co-stimulatory signals, and undergo clonal expansion to differentiate into effector T cells. Germinal centers are primarily for B cell responses. Primary lymphoid tissues (bone marrow and thymus) are where T cells mature but not where activation occurs. Choice D is incorrect as naïve T cell activation does occur in secondary lymphoid tissues.
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Which scientist proposed the concept of clonal selection?
- A. Paul Ehrlich
- B. Macfarlane Burnet
- C. Louis Pasteur
- D. Elie Metchnikoff
Correct Answer: B
Rationale: The correct answer is B: Macfarlane Burnet. Burnet proposed the concept of clonal selection in the 1950s to explain how the immune system recognizes and responds to specific antigens. He suggested that lymphocytes with receptors specific to antigens undergo clonal expansion upon encountering the antigen. This hypothesis laid the groundwork for our understanding of adaptive immunity.
A: Paul Ehrlich developed the side-chain theory of antibody formation, not clonal selection.
C: Louis Pasteur is known for his work in microbiology and vaccination, not clonal selection.
D: Elie Metchnikoff is credited with discovering phagocytosis, not clonal selection.
Which condition is associated with increased susceptibility to bacterial infections due to complement deficiencies?
- A. Asthma
- B. Systemic lupus erythematosus (SLE)
- C. Streptococcus pneumoniae infections
- D. Chronic hepatitis
Correct Answer: C
Rationale: The correct answer is C: Streptococcus pneumoniae infections. Complement deficiencies impair the body's ability to fight bacterial infections, particularly encapsulated bacteria like Streptococcus pneumoniae. Asthma (A), SLE (B), and chronic hepatitis (D) are not directly associated with increased susceptibility to bacterial infections due to complement deficiencies. Asthma is a chronic respiratory condition, SLE is an autoimmune disease, and chronic hepatitis affects the liver. Therefore, only Streptococcus pneumoniae infections are directly linked to complement deficiencies.
The joints most commonly involved with rheumatoid arthritis include:
- A. Symmetrical involvement of major joints.
- B. Small joints of hands and feet.
- C. Spine,from the sacrum upward to cervical.
- D. Slightly movable joints of the axial skeleton.
Correct Answer: B
Rationale: Rheumatoid arthritis primarily affects small joints symmetrically, especially those in the hands and feet. Major joints and axial skeleton involvement occurs but is less characteristic of early disease presentation.
Which condition is an example of Type IV hypersensitivity?
- A. Multiple sclerosis
- B. Grave's disease
- C. Anaphylaxis
- D. Eczema
Correct Answer: A
Rationale: The correct answer is A: Multiple sclerosis. Type IV hypersensitivity involves T cell-mediated immune reactions, leading to tissue damage. In multiple sclerosis, myelin sheath destruction is caused by activated T cells attacking self-antigens.
Incorrect choices:
B: Grave's disease is an example of Type II hypersensitivity involving autoantibodies targeting specific cells.
C: Anaphylaxis is a Type I hypersensitivity reaction mediated by IgE antibodies causing rapid and severe allergic reactions.
D: Eczema is a chronic inflammatory skin condition involving complex immune mechanisms not specific to Type IV hypersensitivity.
How do NK cells kill target cells?
- A. By producing antibodies
- B. Through secretion of cytokines
- C. By releasing perforin and granzyme
- D. By phagocytosis
Correct Answer: C
Rationale: The correct answer is C. NK cells kill target cells by releasing perforin and granzyme. Perforin creates pores in the target cell's membrane, allowing granzyme to enter and induce apoptosis. Antibodies (choice A) are produced by B cells, not NK cells. Cytokines (choice B) regulate immune responses but do not directly kill cells. Phagocytosis (choice D) involves engulfing and digesting pathogens, which is not how NK cells kill target cells.