Theme 1 - tissues Flashcards
what are primary lymphoid tissues
- involved in development and differentiation of lymphocytes
- Thymus (T cells)
- Bursa equivalent tissues (foetal liver and adult bone marrow) B cells
what is the role of secondary lymphoid tissues
what do they include
- allow ANTIGEN ACCUMULATION
- allow ANTIGEN PRESENTATION to both naïve and memory lymphocytes
- include the MUCOSA, LYMPH NODES and SPLEEN
what are the tertiary lymphoid tissues
- comprise all the remaining lymphoid tissues in the body (eg skin)
- contain only a few lymphocytes normally
- may be INVADED during inflammation by unique MEMORY LYMPHOCYTES
what is the role of the thymus
what happens to it with age
structure
how do cells enter
where do they travel to in the thymus during maturation
what affects thymocyte development
what happens to those cells that don’t leave the thymus
- produces LYMPHOCYTES
- provided env for T cell MATURATION and EDUCATION
- SHRINKS with age
- 2 lobes divided into lobules by TRABECULAE
- each lobule has OUTER CORTEX & INNER MEDULLA
- cells enter as THYMOCYTES and surrounded by EPITHELIAL cells and others eg INTERDIGITATING DENDRTIC CELLS and MACROPHAGES
- cells move from CORTEX to MEDULLA while differentiating into T cells
- in cortex THYMIC NURSE cells affect thymocyte development
- if the T cell doesn’t leave, it undergoes APOPTOSIS
what % of original thymocytes make it through the thymus into circulation as naïve T cells
5%
when cells enter thymus as THYMOCYTES what do they express/not express
then what do they express in the next stage
and finally
do not express CD4 or CD8 (double neg) - then express BOTH double positive - finally express one or the other - expression of CD3 and TCR INC as they pass through thymus
what is TCR
T cell receptor
how are thymocytes educated in the thymus
how long is this process
POSITIVELY selected to bind to MHC molecules
NEGATIVELY selected if they bind to SELF peptides
- takes 1-3 weeks
how do B cells develop
what -ve and +ve selection
immature B cells mature under local influence of GROWTH factors (from stromal cells)
- EDUCATED to not bind self molecules, if it does NEGATIVE SELECTION and it will undergo apoptosis
- EDUCATED to respond to SURVIVAL factors (POSITIVE SELECTION)
- then released as naïve B cells which are functionally immature
what % of B cells do not undergo apoptosis and can leave the bone marrow
10%
what is lymoh formed from
blood components from capillaries enter tissues making extracellular fluid that provides food and gas exchange
(tissue fluid)
- extracellular fluid drains into LYMPHATIC VESSELS
what 2 things use lymphatics to migrate around the body
lymphocytes and leukocytes
how are lymphocytes transported around the vessels
bind to ADHESION MOLECULES on the endothelial cells that line blood vessels
- up and down regulation of adhesion molecules allow movement of cells
how is movement in the lymphatics aided
- smooth muscle cell movement
- arterial pressure due to close association with blood vessels
- valves prevent backflow
how are leukocytes transported around the vessels
give an example of the what binds and what it binds to
- use HOMING RECEPTORS (adhesion molecules) to bind to ENDOTHELIUM lining of blood vessels
- LFA-1 binds to ICAM-1 on endothelial cells
what is homing
traffic of cells through body to specific areas
describe the lymph nodes structure size where do cells come from where do they go
- small bean shaped tissue aggregates at junctions of major lymphatic vessels
- 1-25mm diameter, larger if inf
- surrounded by CAPSULE, supported by RETICULUM
- 3 main areas: CORTEX, PARACORTICAL AREA and MEDULLA
- cells flow from cortex–>para–> medulla
- cells enter from HEV (HIGH ENDOTHELIAL VENULES) and return via thoracic duct
- cells drain into EFFERENT LYMPHATIC at the HILUS
which part of the lymph node do T cells collect
paracortical areas
which part of the lymph node do B cells collect
outer cortex
what is found in paracortical area of the lymph node
contains ANTIGEN PRESENTING CELLS,
large LYMPHOCYTES and ACTIVATED cells
what is found in the medulla of the lymph node
PLASMA cells secreting antibody
what is a follicle in the lymph node
B cells forming dense aggregates
- PRIMARY follicles= dense and uniform
- SECONDARY follicles cont larger cells associated with MACROPHAGES forming GERMINAL centres w/ HIGH CELL PROLIFERATION
what are the two parts of the spleen
red pulp and white pulp
what is the function of the red pulp in the spleen
NON IMMUNOLOGICAL:
filters damages or ages cells
what is the function of white pulp in the spleen
IMMUNOLOGICAL ROLE:
develop immune responses
what is PALS
PERIARTERIOLAR LYMPHATIC SHEATH- cells and tissues surrounding major arterial branches
the B dependent area of the spleen consists of what
lymphoid follicles
the T dependent area of the spleen consists of what
PALS
what is MALT
Mucosa-associated lymphoid tissue
describe MALT
diffusely distributed lymphoid tissues in lining of GI, resp and urogenital tracts
- gut-associated lymphoid tissue (GALT) and Bronchus ALT (BALT) are best characterisedBronchus ALT (BALT) a
GALT is made up of what
Peyer’s patches and isolated follicles in colonic submucosa
- lymphocytes also found in lamina propria, intestinal epithelium & in lumen of intestine epithelium & in lumen of intestine
describe Peyer’s patches
- aggregates of lymphocytes; B cells form central follicle surrounded by T cells & macrophages surrounded by T cells & macrophages
- have efferent lymphatics that drain into mesenteric lymph nodes, but lymph nodes, but no afferentno afferent lymphatics lymphatics
- covered by specialised lymphoepithelium consisring of M cells (microfold)
- g in gut enters via M cells that selectively take up particles & deliver them to lymphoid follicles also by particles & deliver them to lymphoid follicles also by specialised dendritic cells which ‘reach’ into the gut specialised dendritic cells which ‘reach’ into the gut lumen
describe BALT
mostly B cells organised into aggregates & follicles with few germinal centres, some M cells but organisation is less germinal centres, than GALT
- cont capillaries, arterioles, venules, HEVs and efferent lymphatics
- suggests BALT may play role in sampling Ag not only from lungs but also from systemic circulationonly from lungs but also from systemic circulation
- greater infiltration of white blood cells following infection (inducible BALT or iBALT)infection (inducible BALT or iBALT)
what are the professional antigen presenting cells
dendritic cells (DC), macrophages, and B cells
