Question 2.1) An infant with recurrent bacterial and fungal infections is suspec

Question

Question 2.1) An infant with recurrent bacterial and fungal infections is suspected to have an immunodeficiency disease. Within two days after exposure to a pathogen, the organisms have proliferated to dangerous levels requiring immediate systemic antibiotic treatment. It is unlikely that this infant has a defect in B or T lymphocyte responses to the infection because:

Choose one that apply.

A) Bacteria and fungi are not efficiently transported to draining lymph nodes to initiate adaptive immune responses.

B) Systemic infections of bacteria and fungi are usually cleared by the spleen.

C) Bacteria and fungi do not require B cell or T cell responses for their clearance.

D)The defective immune response occurs too rapidly following infection to be due to a defect in B or T lymphocytes responses.

E) Adaptive immune responses require dendritic cells to take up and degrade pathogens.

Question 2.2) Epithelial surfaces provide the first line of defense against infection by the use of several types of mechanisms. One of the chemical mechanisms used by epithelia is:

Choose one that apply:

A) Production of mucus, tears, or saliva in the nose, eyes, and oral cavity

B) Secretion of antimicrobial peptides by epithelial cells

C)Peristalsis in the gastrointestinal tract

D) Joining of epithelial cells by tight junctions

E) Movement of mucus by cilia

Question 2.3) When stimulated by binding to bacterial products, the fMet-Leu-Phe (fMLF) receptor triggers multiple responses by phagocytes, including migration and induction of antimicrobial activities. Most of these responses are activated by small GTPases of the Rac and Rho families that are indirectly activated by fMLF receptor stimulation. The fMLF receptor can initiate multiple downstream signaling pathways because:

Choose one that apply:

A) It couples directly to two different guanine nucleotide exchange factors (GEFs).

B) It induces assembly of multiple enzymes from individual cytosolic components.

C) It promotes fusion of phagosomes with lysosomes, initiating multiple signals.

D) It binds to Rac, Rho, and cdc42 directly

E) It couples to a heterotrimeric G protein that has alpha and beta/gamma subunits with independent activities.

Question 2.4) The formation of the C3 convertase is a key step in complement activation that occurs in all three complement pathways. This enzyme cleaves C3 in blood plasma, leading to a conformational change in the C3b fragment that exposes its reactive thioester group. The activated C3b is potentially harmful to the host, if it becomes covalently attached to a host cell, rather than to the surface of a pathogen. This deleterious outcome is largely avoided by:

Choose one that apply:

A) The inability of active C3b to covalently attach to the membranes of eukaryotic cells.

B) The inability of active C3b to diffuse away in the blood plasma.

C) The rapid hydrolysis of active C3b in solution, rendering it inactive.

D) The tight binding of active C3b to the C3 convertase.

E) The ability of active C3b to recruit phagocytic cells.

Question 2.5) Mycobacteria are intracellular pathogens that have adapted to life inside phagocytic cells, such as macrophages. These intracellular bacteria are taken up by phagocytosis, similar to other pathogens, but the bacteria are not killed. One possible mechanism that could account for this immune evasion by mycobacteria is their ability to:

Choose one that apply:

A) Kill the macrophage before it kills them

B) Prevent the expression of antimicrobial peptides in the phagosome

C) Prevent the acidification of phagosomes

D) Prevent fusion of phagosomes with lysosomes

E) Prevent induction of nitric oxide production in the phagosome

Explanation / Answer

Question 2.1: D) The defective immune response occurs too rapidly following infection to be due to a defect in B or T lymphocytes responses.

Question 2.2: B) Secretion of antimicrobial peptides by epithelial cells.

Question 2.3: E) it couples to a heterorimeric G protein that has alpha and beta /gamma subunits with independent activities.

Question 2.4: C) The rapid hydrolysis of active C3b in solution, rendering it inactive.

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