Cutaneous and Mucosal-associated Lymphoid Tissue Flashcards
Mucosal-associated lymphoid tissue
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)
Peyer’s patch
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
Mucous membranes
Mechanical barrier to many pathogens
Tight junctions between cells making penetration difficult
Colonized by normal flora that compete with pathogens
Mucus
Viscous fluid secreted by mucosal epithelial cells
Traps and washes away pathogens
Can contain antibacterial and antiviral substances including lysozyme
Epithelial cells of mucous membranes
Make cytokines that induce local inflammatory response
M cells
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
IgA-synethsizing plasma cells
B cells within lymphoid follicles/Peyer’s patches
Activated by antigen transported by M cells
Differentiate into plasma cells
Secretory IgA
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
IgA transport across membrane
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)
IgM
Pentameric
Transported into mucosal secretions by same mechanism as IgA
Small amounts
Intraepithelial lymphocytes
Many different categories:
- T cells that express TCR with limited diversity
- Have TCR that interact with microbial phospholipids (no MHC presentation)
- Recognize stress-induced MHC-like molecules
- 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
CD1
Nonclassical class I MHC-like molecules
Mucosal mast cells
Secrete range of cytokines following triggering of pattern recognition receptors (ie. TLR) that recognize bacterial products
TLR4
Recognizes lipopolysaccharide
TLR2
Recognized peptidoglycan
Lymphocyte trafficking to MALK
Lymphocytes activated in MALT recirculate in blood and home in to mucosal tissues
Homing mediated by vascular addressins
Vascular addressins
Homing of lymphocytes to tissue
MadCAM1
Mucosal addressing cell adhesion molecule
Found in Peyer’s patches
Cutaneous-associated lymphoid tissue
Skin
Important mechanical barrier to infection
Epidermis
Several outer layers of tightly-packed epithelial cells
Includes specialized epithelial cells, keratinocytes
Dermis
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
Sebum
Secreted by sebaceous glands
Creates acidic environment that inhibits growth of many microorganisms
Sweat
Contains lysozyme
Keratinocytes
Secrete cytokines that induce local inflammatory responses Can be induced to express class II MHC
Skin mast cells
Secrete cytokines that induce local inflammatory responses
Langerhans cells
Within epidermis
Immature dendritic cell that internalizes antigen
Transports antigen to regional lymph nodes by lymphatic vessels
Differentiate in nodes into interdigitating dendritic cells
Mature dendritic cells
Express high levels of class II MHC molecules and costimulatory ligands (CD80/CD86) that allow for potent activation of naive CD4+ T helper cells
Intraepidermal lymphocytes
Mostly T cells that express TCR with limited diversity
First line of host defences
