Chapter 13

Question 1

The main regional

immune systems are where?

Answer 1

in the gastrointestinal tract
and skin, which together protect against microbial
invasion across an enormous surface area of exposure to the environment.

Question 2

The gastrointestinal immune system must cope

with the presence of trillions of commensal bacteria in the gut lumen how?

Answer 2

by preventing their invasion
and tolerating their presence in the lumen, while
also identifying and responding to numerically
rare pathogenic organisms

Question 3

Innate immunity in the gastrointestinal system is
mediated in part by the mucosal epithelial lining
cells, which does what?

Answer 3

impede microbial invasion by tight
intercellular junctions, secretion of mucus which
prevents microbial attachment to the lining cells,
and the production of antimicrobial molecules,
such as defensins

Question 4

Innate immune effector cells in

the lamina propria include what?

Answer 4

macrophages, DCs, and
mast cells. Intraepithelial lymphocytes, including
γδ T cells, also provide innate defense against commonly a encountered microbes at the intestinal
epithelial barrier

Question 5

Specialized anatomic features of

adaptive immunity in the intestinal tract include what?

Answer 5

collections of lymphoid tissues just below the epithelial lining that comprise the gut-associated lymphoid tissues (GALT), including oropharyngeal
tonsils, Peyer’s patches in the ileum, and similar
collections in the colon

Question 6

M cells in the epithelial

lining do what?

Answer 6

sample lumen antigens and transport them

to antigen-presenting cells in the GALT

Question 7

Lamina

propria DCs extend processes through what?

Answer 7

intestinal
epithelial lining cells to sample lumenal antigens.
There are also diffuse effector lymphocytes in the
lamina propria of the gut and in mesenteric lymph
nodes, where many of the adaptive immune
responses in the bowel wall are initiated

Question 8

Effector B and T lymphocytes that differentiate
from naive T cells in the GALT or mesenteric
lymph nodes enter where and do what?

Answer 8

enter the circulation, and selectively
migrate back to the intestinal lamina propria. This
tissue-specific homing is due to signals the naive
T cells receive from DCs in the GALT and mesenteric nodes, including retinoic acid derived from
dietary Vitamin A, which induce expression of
chemokine receptors and adhesion molecules on
the differentiated effector cells that favor homing
back to the gut

Question 9

Humoral immunity in the gastrointestinal tract is
dominated by IgA secretion into the lumen, where
the antibodies do what?

Answer 9

neutralize potentially invading

pathogens

Question 10

B cells in the GALT and mesenteric

lymph nodes differentiate into what?

Answer 10

IgA-secreting
plasma cells under the influence of TGFβ, BAFF,
and other cytokines, through both T-dependentand T-independent mechanisms, and the plasma
cells migrate to the lamina propria beneath the
epithelial barrier and secrete IgA

Question 11

Dimerized IgA is

transported across the epithelium by who?

Answer 11

the poly-Igreceptor and released into the lumen. IgA is also
secreted into breast milk, and mediates passive
immunity in the gut of breastfeeding infants

Question 12

TH17 cells play a dominant role in what?

Answer 12

n T cell–mediated
immunity in the intestinal tract, in part because
IL-17 and IL-22, which they secrete, enhance epithelial barrier function

Question 13

TH2 cells are important in

defense against what?

Answer 13

against intestinal parasites. Changes in
bacterial flora can influence the balance between
different helper T cell subset responses, both in the
gut and systemically throughout the adaptive
immune system

Question 14

Immune reposes to commensal organisms and
food antigens in the lumen of the intestinal tract
are minimized by a variety of mechanisms, including what?

Answer 14

selective expression of pattern recognition
receptors in the cytoplasm and basolateral surfaces
of the epithelial lining cells, and sampling of
luminal microbial antigen by DCs which are specialized to induce Treg that suppress adaptive
immune responses

Question 15

Several cytokines are essential
to maintain immune homeostasis is the bowel
wall, including which ones?

Answer 15

TGFβ, IL-10, and IL-2. Systemic
tolerance to some antigens can be induced by
feeding the antigens to mice, a phenomenon called
oral tolerance.

Question 16

Several intestinal diseases are related to abnormal
immune responses, including inflammatory bowel
diseases (Crohn’s disease and ulcerative colitis), in
which what happens?

Answer 16

innate and adaptive immune responses to
normal gut flora are not adequately regulated, and
celiac disease, in which humoral and cell-mediated
responses to dietary wheat glutens occur

Question 17

Mucosal immunity in the respiratory system

defends against what?

Answer 17

against airborne pathogens, and is the

cause of allergic airway diseases, such as asthma

Question 18

Innate immunity in the bronchial tree depends on

the ciliated epithelial lining, which secretes what?

Answer 18

mucus
and defensins and moves the mucus with entrapped
microbes out of the lungs.

Question 19

As in the intestines, regulatory mechanisms, including Treg and
immunosuppressive cytokines are important for what?

Answer 19

prevention harmful responses to nonpathogenic
organisms or other inhaled antigens inhaled
antigens.

Question 20

The cutaneous immune system defends against

microbial invasion how?

Answer 20

through the skin, and suppresses responses against numerous commensal
organisms. The outer multilayered keratinized
squamous epithelial layer, called the epidermis,
performs innate immune defense functions, providing a physical barrier to microbial invasion

Question 21

what do keratinocytes do?

Answer 21

Keratinocytes secrete defensins as well as inflammatory cytokines in response to various PAMPs
and DAMPs. The dermis contains a mixed population of mast cells, macrophages, and DCs
that respond to microbes and injury and mediate
inflammatory responses.

Question 22

DCs are abundant in the skin and mediate innate

immune responses. These DCs also do what?

Answer 22

transport
microbial and environmental antigens that enter
through the skin to draining lymph nodes where
they initiate T cells responses

Question 23

Skin-derived

DCs provide signals, including Vitamin D, to who?

Answer 23

the
naive T cells they activate in draining lymph,
which induce chemokines and adhesion molecules
that favor homing of the effector T cells back to
the skin

Question 24

A significant fraction of the body’s T cells are

present in the skin. Most of these T cells are what?

Answer 24

CD4+
or CD8+
effectors or memory T cells in the dermis

Question 25

TH1, TH2, and TH17 cells are important for defense

against what?

Answer 25

different types of skin-invading pathogens,

while TH1 and TH17 cells contribute to inflammatory dermatoses such as psoriasis.

Question 26

Immune privileged sites, which are tissues where

immune responses are not readily initiated, include what?

Answer 26

the brain, anterior chamber of the eye, and testis

Question 27

The mechanisms of immune privilege include what?

Answer 27

the
tight junctions of endothelial cells in blood vessels
at these sites, local production of immunosuppressive cytokines, and expression of cell surface molecules that inactivate or kill lymphocytes

Question 28

Mammals have evolved mechanisms that prevent what?

Answer 28

maternal immunologic rejection of the developing
fetus, which invariably expresses paternal antigens
that are allogeneic to the mother. These mechanisms appear to act locally at the placental maternal-fetal interface, since systemic maternal
tolerance to paternal alloantigens does not occur

Question 29

what are some examples of the mechanisms used to prevent maternal immunologic rejection of the developing fetus?

Answer 29

include lack of MHC expression on fetal trophoblasts, expression of immunosuppressive cytokines, the actions of Treg, and
local indolamine 2,3-dioxygenase mediated depletion of tryptophan needed for lymphocyte growth.