Ch. 14 Book Questions Flashcards
Which of the following is a common feature important to immune defense in skin and gastrointestinal tract?
a. Epithelial cell lined barriers
b. Production of mucus
c. Synthesis of retinoic acid from vitamin A
d. Paneth cells
e. Keratin layer
a. Epithelial cell lined barriers
Both skin and gastrointestinal tract are continuously lined by tightly joined epithelial cells, which form barriers surfaces of very large surface area. These epithelial surfaces serve as physical and biochemical barriers to invasion by microbes. Gastrointestinal epithelial cells produce mucus, which impedes microbial contact with epithelial cells. Skin epithelial cells do not produce mucus. Retinoic acid synthesis occurs in the gut, where Vitamin A is absorbed, but not appreciably in the skin. Vitamin A has important immunological consequences (on DC and T cell differentiation and homing). Paneth cells are specialized intestinal epithelial cells with important innate immune properties. A tough keratin layer, produced by skin but not gastrointestinal epithelial cells, provides physical protection against microbe invasion.
One of the unique challenges facing the immune system is presence of many commensal non-pathogenic organisms on all the major barrier interfaces, including intestinal mucosa and skin. Our immune systems must be able to tolerate these commensals, while maintaining the ability to respond to invasion by these organisms and to respond to luminal pathogens. Which of the following statement about the relationship between the human microbiome and host is accurate?
a. Commensal organisms on the skin or in the gut do not evoke strong immune responses if they invade through the a damaged epithelial barrier
b. During pathogenic bacterial infections in the gut, the pathogen usually outnumbers nonpathogenic commensals
c. The microbiome on the skin or in the gut lumen has little influence internal immune responses to antigens at other sites
d. Although there are normally millions of bacterial organisms in the gut, most of these belong to only two major genera, Escherichia and Lactobacillus
e. A human normally harbors about 10 times more microbial cells as human cells
e. A human normally harbors about 10 times more microbial cells as human cells
A healthy human carries about 1014 microorganisms, which is about 10 times the number of human cells. Although the vast a majority of these organisms are commensals and do not normally cause disease, if they breach the epithelial barrier, most are capable of inciting strong innate responses that can clear the infection and/or may contribute to significant disease, such as sepsis. Intestinal pathogens remain a tiny minority of the total number of bacteria, even during active disease caused by the pathogen. Gut flora comprise many hundreds of species in over 10 genera. Escherichia and Lactobacillus together comprise a minority of the gut flora.
Defensins are an important part of the innate defense against bacterial invasion in the gut, and abnormalities in defensin production have been associated with various diseases. Which of the following statement about defensins is true?
a. Defensins are peptides that exert lethal toxic effects on bacteria by blocking protein synthesis
b. In the small bowel, the α-defensins are produced by Paneth cells located at the base of crypts
c. Human defensins are secreted in a fully active form by cells in the gut after IL-1 stimulation
d. Mast cell granules are rich in α-defensins
e. Defensins are not produced in the colon
b. In the small bowel, the α-defensins are produced by Paneth cells located at the base of crypts
Paneth cells located at the base of crypts of the small bowel are a major source of defensins. Defensins are peptides that exert lethal toxic effects on microbes by inserting into and causing loss of integrity of their outer phospholipid membranes. They are not inhibitors of protein synthesis. In addition, neutrophil granules, but not mast cell granules, are rich in α-defensins. Human defensins are produced constitutively by Paneth cells as inactive precursor proteins and active defensin peptides are generated by trypsin mediated cleavage. In the colon, β-defensins are produced by absorptive epithelial cells in the intestinal crypt.
The immune system associated with mucosal tissues includes organized lymphoid structures where specialized adaptive immune responses are initiated. Which of the following is not included in mucosal associated lymphoid tissues?
a. Tonsils
b. Peyer’s patches
c. Axillary lymph nodes
d. Mesenteric lymph nodes
e. Adenoids
c. Axillary lymph nodes
Axillary lymph nodes drain the skin and soft tissues of the upper extremities, and not mucosal tissues. Tonsils and adenoids are sites of adaptive immune responses to microbes in the oral cavity and pharynx. Peyer’s patches and mesenteric nodes are sites of initiation of adaptive immune responses to microbes in the gut.
Adaptive immunity to pathogens in the intestinal lumen is mediated in part by antibodies. Which of the following statements about these antibodies is true?
a. They are mainly IgM antibodies
b. They are secreted by B cells located in the gut lumen
c. The B cells that secrete the antibodies are first activated and differentiate in gut associated lymphoid tissues
d. IL-12 is required for B cells to class switch to the isotype of these antibodies
e. The homing of B cells that produce these antibodies to the gut depends on the expression of VLA-4 (α4β7) integrin.
c. The B cells that secrete the antibodies are first activated and differentiate in gut associated lymphoid tissues
Most of the antibodies in the gut lumen are IgA antibodies, secreted by lamina propria B cells that were primed and differentiated in mucosal associated lymphoid tissues (e.g Peyer’s patches). TGFβ, and not IL-12, is the main cytokine driving isotype switching to IgA, but other non cytokine factors are also involved. The IgA producing B cells then enter the blood and home back to the lamina propria. B cell migration out of lamina propria venules depends on expression of the α4β7 integrin and CCR9 on the B cells. The IgA that is secreted in the lamina propria is transported across the gut epithelium into the lumen by the poly-Ig receptor.
What are M cells?
a. A type of mucosal B cell that secretes IgM
b. Lamina propria macrophages that ingest bacteria that have invaded through the intestinal epithelium
c. Alveolar macrophage that secrete surfactant
d. Specialized intestinal epithelial cells that transport antigens or microbes into Peyer’s patches
e. A type of intestinal dendritic cell that tolerizes T cells to food antigens.
d. Specialized intestinal epithelial cells that transport antigens or microbes into Peyer’s patches
M cells are intestinal epithelial cells with short villi, and engage in transport of intact microbes or molecules across the mucosal barrier into gut-associated lymphoid tissues, such as Peyer’s patches, where they are handed off to DCs.
The human skin contains about 10 billion T cells. Most of these T cells have which of the following phenotypes?
a. Memory T cells
b. Naïve T cells
c. Th17 cell
d. Regulatory T cells
e. CD8+ T cells
a. Memory T cells
Most of the skin T cells are in the dermis, and have an effector memory phenotype. They are a mixture of CD4+ and CD8+ T cells.
