What happens to CD4CD8 doublepositive cells in the

Question 1 of 5

What happens to CD4-CD8 double-positive cells in the thymus when they do not recognize MHC molecules?

A. They start proliferating B. They become CD4+ T cells C. They become CD8+ T cells D. They die of apoptosis

Correct Answer: D

Rationale: Double-positive thymocytes that fail to recognize MHC undergo apoptosis during negative selection; they don't proliferate or differentiate (B, C) without MHC interaction.

Question 2 of 5

What are the two pieces of information required for a Th cell to make a decision about which cytokines to produce?

A. What type of invader and where it is located B. How virulent the invader is and what type of immune response is required C. How long the invader has been present and what type of cells are infected D. How much damage the invader has caused and what type of toxins it produces

Correct Answer: A

Rationale: Th cells decide cytokines based on invader type and location ; virulence , duration , and damage are less specific.

Question 3 of 5

What is the function of Th17 cells in the intestinal immune defense?

A. To produce IL-10 and TGFB to calm down the mucosal immune system B. To produce IFNÎ³ and oversee the production of IgG C. To recruit neutrophils and stimulate mucus production D. To produce cytokines to strengthen the TJs and facilitate IgA to go into the lumen

Correct Answer: C

Rationale: Th17 cells recruit neutrophils and boost mucus via IL-17 ; IL-10/TGF-Î² is Treg, IFN-Î³/IgG is Th1, TJ/IgA is partial."To suppress the activation of potentially self-reactive T cells

Question 4 of 5

Which of these is not a non-specific defense mechanism?

A. bacteria B. stomach pH C. antibodies D. skin sebaceous glands

Correct Answer: C

Rationale: Antibodies are specific defenses; bacteria aren't defenses, stomach pH and sebaceous glands are nonspecific.

Question 5 of 5

Women with urinary tract infections caused by E. coli are generally treated with a course of antibiotics. A common complication of the antibiotic treatment is the occurrence of a vaginal yeast infection caused by Candida albicans, an organism that is normally present in very low numbers in the human vaginal tract. This complication occurs because:

A. The E. coli infection damages the reproductive epithelium, causing a breach in the tight junctions and allowing invasion by the Candida albicans B. The E. coli infection induces adhesion molecule expression on the reproductive epithelium, allowing attachment of the yeast C. The antibiotic treatment kills all strains of fungi present in the reproductive tract, except the Candida albicans D. The E. coli infection causes gastrointestinal distress leading to diarrhea

Correct Answer: D

Rationale: Antibiotics disrupt commensal bacteria, allowing Candida overgrowth ; epithelium damage , adhesion , or selective killing don't explain this.

What happens to CD4-CD8 double-positive cells in the thymus when they do not recognize MHC molecules?

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