Mucosal immunity Flashcards
what are primary lymphoid organs
sites where b and T cells are made and matured
where are the primary lymphoid organs
bone marrow
thymus
what are the secondary lymphoid organs
sites where b and T cells can recognise antigen and become activated to fight infection or cancer
where are the secondary lymphoid organs
lymph nodes
spleen
mucosa associated lymphoid tissues/MALTs
capsulated lymphoid tissues
lymph nodes
spleen
non-capsulated lymphoid organs
mucosa associated lymphoid tissues
50% of bodies lymphoid tissue
what are capsulated lymphoid tissues designed for
to control what comes in from outside and keep things trapped inside
function of the spleen
as a filter for blood
not supplied by lymphatic vessels
responds to systemic infections
more lymphocytes flow through spleen than all lymph nodes at any given time
how do antigens and lymphocytes enter the spleen
via the splenic artery
2 distinct regions of the spleen
white pulp
red pulp
separated by a diffuse marginal zone
differences between lymph nodes and spleen
lymphocytes enter via artery
and immune response occurs in the periarteriolar lymphoid sheath
red pulp function
contains mainly macrophages, RBCs and some lymphocytes
old and damaged RBCs are phagocytose in the red pulp
white pulp function
mainly surrounds arteries in the spleen
forms periarteriolar lymphoid sheath
predominantly T cells
marginal zone function
at the edge of the PALS
made of mainly B cells
contain primary lymphoid follicles
process of immune response in the spleen
foreign antigen carried into the spleen from the splenic artery into the marginal zone and captured by dendritic cells
dendritic cells and T cells move to the PALS from the splenic artery
PALS the dendritic activate T helper cells
active T helper cells activate B cells and activated B and helper T move to the primary follicles in the marginal zone
leads to the production of a secondary follicle with germinal centre
lymph nodes
clustered at junctions of lymphatic channels, entrap pathogens entering the lymphatic system from the tissues
bean-shaped structures, comprising a mesh-like reticular framework , packed with lymphocytes, macrophages and dendritic cells
lymph nodes and immune response
lymph flows into the node through lymphatic channels, empty into the sub capsular space carrying APCs and free antigens
lymph percolate inwards, allows phagocytic cells to entrap any bacteria in the lymphatic fluid
a single efferent vessel leaves the lymph node
lymph nodes enlarge when immune response occurs
fluid in the efferent lymphatic vessel
contains antibodies and 50x higher concentration of lymphocytes due to proliferation of lymphocytes within the node
production of secondary follicle in lymph node
antigen and APC from tissue travel to lymph node in the lymphatic fluid
antigens processed by resident dendritic cells in the paracortex
dendritic cells and B cells activate antigen specific T helper cells
B cells also activated in the paracortex by antigen directly via the BCR and any helper T cells
activated B and helper T form foci with proliferating B cells
B cells and helper T cells migrate to primary follicles of the cortex and interact with follicular dendritic cells
production of secondary follicle with germinal centre and production of plasma cells
what are lymphoid follicles
collections of lymphocytes and dendritic cells, in all secondary lymphoid tissue
primary follicles
collection of mainly inactive B cells, macrophages and follicular dendritic cells
what occurs when germinal centres are formed
the follicle is called a secondary follicle
what happens when activate dB cells and helper T cells move into follicles
proliferate forming germinal centres
germinal centres
B cells proliferate and undergo somatic hypermutation to make better antibodies
inactive B cells pushed towards age to form mantle zone
B cells surrounded by cuff of T helper cells
what is occurring in the dark zone
cell proliferation
what is occurring in the light zone
cell death
somatic hypermutation
immunoglobulin gene sequences are further mutated after rearrangement and binding to their antigen
introduces point mutations at a high rate
V sequences not C sequences are mutated
B cells mutate in dark zone of a germinal centre
advantages of V sequence mutations
more diversity
higher affinity
because the mutations are random what may happen
some BCRs have detrimental
some B cells have favourable mutations
BR detrimental mutations
less able to bind to the antigen
can recognise self proteins
leads to apoptosis of B cells
favourable mutations
many Able to bind the foreign antigen- increased affinity
leads to selection of B cells with highest affinity BCRs through interaction of follicular T helper cells, affinity maturation
BCR less good at binding antigen
doesn’t bind antigen as well as other BCRs
cell doesn’t capture, process and present antigen to T cell
B cel doesn’t receive T cell help and dies
BCR better at binding antigen
binds antigen better than others
Cell captures, process and presents antigen to the T cell
B cell receives T cell help, proliferates and differentiates to plasma cell
what follows somatic hypermutation and selection of high affinity B cell by affinity maturation
B cells move further into the light zone
receive a second survival signal from a T helper cell
causes differentiation into either plasma cells or memory B cells
can induce class switching of antibody
class switching
B cells
make different types or isotopes with different constant regions
each isotope has different characteristics and binds to different Fc receptors on cells
what does the variable region do
determine antigen specificity
what does the constant region do
determine antibody class
label the antibody
top left up to the first dip= variable region
bottom left fro the dip to the bottom= constant region
bottom of two chains= Fc region
blue= heavy chain
orange=light chain
specific hole in the top= FAB region
which kinds of antibodies are important in MALT
IgA and IgD
if barriers are breached what do mucosa have
draining lymph nodes
MALTs
perpetually activated innate and adaptive immune cells throughout epithelium and lamina propria
what do MALTs do
defend body against pathogen entry via mucous membranes
more plasma B cells than in lymph, spleen and. bone marrow
2 types of MALT tissue
BALTs
GALTS
what does BALT stand for
bronchus-associated lymphoid tissue
what does GALT stand for
gut-associated lymphoid tissue
GALTs
peyers patches in the small intestine
isolated lymphoid follicles
lamina propria immune cells
appendix
palatine tonsils
adenoids
lingual tonsils
all support the mesenteric lymph node
where are tonsils found q
lingual
palatine
nasopharyngeal
tonsils
nodular structure with meshwork of reticular cells, macrophages, granulocytes and mast cells
B cells organised into discrete follicles and germinal centres surrounded by cuff of T cells
defends against antigens entering nasal and oral epithelia
inductive sites
where B and T cells re primed by antigen and differentiate into effector cell
effector sites
where B and T cells migrate to carry out effector function to clear pathogens
Peyers patches
inductive sites
30-40 lymphoid nodules
distal small intestine
nodules contain follicles developing into germinal centres on antigen exposure
closely associated with intestinal epithelium
microfold cells
M cells
occur at inductive sites
have broad process in contact with lumen
deep invagination or pocked in basal membrane
filled with B cells, T cells, dendritic and macrophages
antigen in M cells
from the lumen of digestive, respiratory or urinary tract is phagocytosed
transported and released into basolateral pocket of cell
antigen taken up by dendritic cells leading to activation or tolerisation of T and B cells in lamina propria
examples of immune cells
goblet
cytotoxic t cells
plasma
goblet cells
produce mucu
cytotoxic T cells
rapidly eliminate infected epithelial cells
plasma cells
secrete IgA and IgD
what is an AMP
antimicrobial peptide
