Immune cell and organs Flashcards
What is the function of secondary lymphoid organs?
Where lymphocytes can interact with antigen and with other lymphocytes, including spleen, LNs, MALT
In an embryo where does haematopoietic occur?
amniotic sac
In a fetus where does haematopoiesis occur?
all bones, liver + spleen
Where does haematopoiesis occur in adults? 5 sites
- Flat bones
- Vertebrae
- Iliac bones
- Ribs
- End of long limbs
What is the broad structure of the thymus?
bilobed, medulla + cortex regions
What is the role of the Hassalls’ corpuscle in the thymus?
secretes soluble factors + is important in regulatory T cells
Is there a change in the thymus during the immune response to antigens?
no - continuous development of T cells
What volume of lymph is returned to the blood each day + how?
2-3L of lymph, via superior vena cava
What is the size + shape of lymph nodes?
kidney shaped, >1cm
How does lymph enter + exit LNs?
- enters via afferent vessel
- exits via efferent
- lymph percolates through all lymphocytes before leaving the node
What is meant by a lymph node being described as a summative junction?
there are many afferent vessels but one efferent vessel
What is meant by a lymph node being described as a summative junction?
there are many afferent vessels but one efferent vessel
How do lymphocytes enter the lymph nodes?
rich blood supply lets lymphocytes into the LNs via high endothelial venules
Which part of the lymph node is the T cell area?
parafollicular cortex
Which part of the lymph node is the B cell area?
lymphoid follicle - mostly on periphery of the lymph node
What leads to the generation of a germinal centre in a lymph node?
during immune response there is massive proliferation of B cells
What targets respective lymphocytes to their specific areas of the LN?
specific chemokines
What is a function of the spleen?
filter for antigens in the blood
What 2 regions is the spleen broadly split into?
white pulp + red pulp
What is the white pulp of the spleen?
lymphoid cells around blood vessels, full of lymphocytes
What is the white pulp of the spleen?
lymphoid cells around blood vessels, full of lymphocytes
What 3 areas is the white pulp of the spleen further divided into?
- Peri-arteriolar lymphatic sheath (PALS) = T cell area
- Splenic lymphoid follicles
- Marginal zone
Where are the B cell lymphocytes located in the spleen?
follicles
What may be contained within the follicles of the spleen?
germinal centres - form upon antigenic stimulation
What is the marginal zone of the spleen?
interface of red pulp with PALS and follicles
What is the function of the marginal zone of the spleen?
contains macrophages, screens systemic circulation for antigens + pathogens, role in antigen processing
Where does the gut-associated lymphoid tissue drain?
involved in mesenteric lymphatic drainage system to mesenteric LNs, including intraepithelial lymyphocytes
What are the 2 components fo the gut-associated lymphoid tissue?
- Peyer’s patches
- M-cells
What are Peyer’s patches formed of?
non-capsulated aggregation of lymphoid tissue - predominantly B lymphocytes and contain germinal centres during immune responses
What is the function of M cells of the gut-associated lymphoid tissue?
sample contents of the intestine, surveying for pathogens which they can then deliver to immune cells
Label the following on the GALT diagram: villus, crypt, M cell, Peyer’s patch.
What are 3 types of immune cells within the epidermis of the skin?
- keratinocytes
- Langerhans cells
- Intraepidermal lymphocytes
What are 2 types of immune cells present in the derm of the skin which heavily guard the epidermis?
- Macrophages
- T lymphocytes
What structures exist within the dermis of the skin which assist with its immune function?
venules + lymphatic vessels - provides entry to the blood circulation + drainage to regional lymph node
How does the body ensure that antigen meets lymphocyte with the specific receptor for it?
lymphocyte recirculation - pathogen is on mucosal surface, naive lymphocytes leave the bone marrow + thymus + enter bloodstream, reirculate through peripheral lymphoid tissue -> recognise antigen leading to massive B cell proliferation in secondary lymphoid tissue
What happens to lymphocytes if they don’t recognise specific antigen?
die
When does extravasation of naive T cells into the lymph nodes occur?
during the immune response
What are 4 steps of the physical process of extravasation of a naive T cell into a lymph node?
- naive T cell rolls along epithelium
- stopped + activated by specific chemokines at a particular place on the epithelium - place it stops determined by selectins
- integrins increase adhesion of the T cell to the epithelium, leading to arrest of the cell
- transendothelial migration of T cell into LN occurs
How do antigens enter lymph nodes?
via draining lymphatics
What is the role of selectins in T cell extravasation into LNs?
stop the lymphocyte at a particular place on the epithelium
What is the role of integrins in the extravasation of T cells into the LN?
increase adhesion of the T cell to the epithelium leading to cell arrest
How many times do naive T cells circulate?
once per day
How do T cell lymphocytes enter the lymph nodes?
high endothelial venule
Where does the naive lymphocyte get activated by antigen?
within the lymph node after entering via high endothelial venule
What happens after a lymphocyte is activated within a lymph node?
stops recirculating - massive proliferation of B lymphocytes - re-enter blood via SVC + target invading microbes/pathogens
How many CD markers exist?
> 300
What CD surface marker is expressed by all T lymphocytes?
CD3-antigen specific receptor (TCR)
What are 2 types of TCR and their breakdown in terms of proportion of T lymphocytes in blood?
- γδ TCR - 10%
- αβ TCR - 90%
What is the breakdown of αβ TCR expression cells in terms of which express CD4 and whcih CD8?
- CD4: 2/3
- CD8: 1/3
What is the function of CD4+ cells?
T helper cells, regulatory T cells - secrete cytokines
What is the function of CD8+ cells?
cytotoxic T cells - lyse infected cells, secrete cytokines
What happens to ability to respond to new infections with age? What happens to the total number of T cells with age?
- reduced ability to respond to new infections, as thymic output declines with age + thymus atrophies
- total number of T cells doesn’t change - just more memory cells
What is the only situation when T lymphocytes can recognise antigen?
using T cell receptor when antigen presented at surfce of another cell; antigen is presented by an MHC molecule
What molecule is presented on a ll B lymphocytes? What is the function of this?
MHC class II - can present ntigen to helper T cells
How can B lymphocytes recognise antigen?
intact antigen free in body fluids (so not presented by another molecule, unlike T cells)
How can B lymphocytes recognise antigen?
intact antigen free in body fluids (so not presented by another molecule, unlike T cells)
What forms the B cell receptor?
a membrane-anchored form of antibody linked to signalling subunits
What are 4 types of APCs?
- dendritic cells
- B lymphocytes
- macrophages
- follicular dendritic cells
Where are each of the key 4 types of APCs located?
- DCs: widely spread e.g. skin + mucosal tissue
- B cells: lymphoid tissue
- Macrophages: lymphoid tissue
- follicular dendritic cells: lymph node follicles
What do each of the 4 types of APC present antigen to?
- DCs: T cells
- B cells: T cells
- Macrophages: T cells
- follicular dendritic cells: B cells
