Cutaneous and Mucosal-associated Lymphoid Tissue

Question 1

Mucosal-associated lymphoid tissue

Answer 1

Present in digestive, respiratory, urogenital systems
Defend from pathogens
Have clusters of lymphoid cells
Include Peyer’s patches
Contain large population of IgA secreting plasma cells and intraepithelial lymphocytes (mainly T cells)

Question 2

Peyer’s patch

Answer 2

Found in submucosal layer of intestine, tonsils and appendix
Contain B lymphocytes organized into primary follicles and germinal centres
T cells are found around germinal centres

Question 3

Mucous membranes

Answer 3

Mechanical barrier to many pathogens
Tight junctions between cells making penetration difficult
Colonized by normal flora that compete with pathogens

Question 4

Mucus

Answer 4

Viscous fluid secreted by mucosal epithelial cells
Traps and washes away pathogens
Can contain antibacterial and antiviral substances including lysozyme

Question 5

Epithelial cells of mucous membranes

Answer 5

Make cytokines that induce local inflammatory response

Question 6

M cells

Answer 6

Specialized epithelial cells
Flattened, transport antigen from lumen of respiratory, digestive and urogenital tracts to underlying MALT, into pocket by vesicles
Pocket is filled with B cells, T cells and macrophages
Found at inductive sites that overlie organized lymphoid follicles in lamina propria

Question 7

IgA-synethsizing plasma cells

Answer 7

B cells within lymphoid follicles/Peyer’s patches
Activated by antigen transported by M cells
Differentiate into plasma cells

Question 8

Secretory IgA

Answer 8

Exceeds any other Ig per day
Line of defence against bacteria/viruses
Transported across epithelial and released into lumen
Polymeric structure
Traps large antigens that are eliminated by cilia or peristalsis
Prevents receptor mediated attachment
Dimer or tetramer of IgA, J chain and 70kDA secretory component that masks cleavage sites in hinge region to protect from enzymatic digestion

Question 9

IgA transport across membrane

Answer 9

IgA-secreting plasma cells in sub epithelial tissue
Secreted IgA binds to poly-Ig receptor expressed on basolateral surface by the J chain
Transported in vesicle across epithelium to lumen
Poly-Ig receptor is cleaved, and becomes the secretory component (70kDa)

Question 10

IgM

Answer 10

Pentameric
Transported into mucosal secretions by same mechanism as IgA
Small amounts

Question 11

Intraepithelial lymphocytes

Answer 11

Many different categories:

1. T cells that express TCR with limited diversity
2. Have TCR that interact with microbial phospholipids (no MHC presentation)
3. Recognize stress-induced MHC-like molecules
4. NKT with TCR that fact with bacteria-derived glycolipids antigens presented by CD1 molecules on APCs

Secrete cytokines that shape adaptive immune response
Some are cytotoxic

Question 12

CD1

Answer 12

Nonclassical class I MHC-like molecules

Question 13

Mucosal mast cells

Answer 13

Secrete range of cytokines following triggering of pattern recognition receptors (ie. TLR) that recognize bacterial products

Question 14

TLR4

Answer 14

Recognizes lipopolysaccharide

Question 15

TLR2

Answer 15

Recognized peptidoglycan

Question 16

Lymphocyte trafficking to MALK

Answer 16

Lymphocytes activated in MALT recirculate in blood and home in to mucosal tissues
Homing mediated by vascular addressins

Question 17

Vascular addressins

Answer 17

Homing of lymphocytes to tissue

Question 18

MadCAM1

Answer 18

Mucosal addressing cell adhesion molecule

Found in Peyer’s patches

Question 19

Cutaneous-associated lymphoid tissue

Answer 19

Skin

Important mechanical barrier to infection

Question 20

Epidermis

Answer 20

Several outer layers of tightly-packed epithelial cells

Includes specialized epithelial cells, keratinocytes

Question 21

Dermis

Answer 21

Thicker inner layer composed of connective tissue
Contains blood vessels, hair follicles, sebaceous glands and sweat glands
Contains CD4+ and CD8+ T cells (most part previously activated or memory cells) and macrophages

Question 22

Sebum

Answer 22

Secreted by sebaceous glands

Creates acidic environment that inhibits growth of many microorganisms

Question 23

Sweat

Answer 23

Contains lysozyme

Question 24

Keratinocytes

Answer 24

Secrete cytokines that induce local inflammatory responses
Can be induced to express class II MHC

Question 25

Skin mast cells

Answer 25

Secrete cytokines that induce local inflammatory responses

Question 26

Langerhans cells

Answer 26

Within epidermis Immature dendritic cell that internalizes antigen Transports antigen to regional lymph nodes by lymphatic vessels Differentiate in nodes into interdigitating dendritic cells

Question 27

Mature dendritic cells

Answer 27

Express high levels of class II MHC molecules and costimulatory ligands (CD80/CD86) that allow for potent activation of naive CD4+ T helper cells

Question 28

Intraepidermal lymphocytes

Answer 28

Mostly T cells that express TCR with limited diversity | First line of host defences