Lymphoid System - Part 1 Flashcards
central lymphoid organs?
- bone marrow
- thymus
what is bone marrow a source of?
stem cells
-B cells derived from stem cells reside in non-thymic lymphoid organs
what is thymus a source of?
stem cells from bone marrow mature to T cells here
where are B cells derived from?
bone marrow lymphoid progenitor cells
describe differentiation of B cells
interaction w/ T helper/macrophages results in clonal expansion and antibody producing plasma cells and memory B cells (important in secondary antibody response)
what do B cells recognize?
free antigen peptides not bound to MHC complex
what do T cells recognize?
respond to cell-bound antigens
T helper cells
- CD4+
- interact w/ B cell/macrophage to stimulate response to foreign antigen
- recognize MHC II on antigen presenting cells
two subclasses of T helper cells
- Th1: important in response to viral and bacterial infection
- Th2: important in response to parasitic infection
T cytolytic/cytotoxic cells
- CD8+
- recognize MHCI on antigen-presenting cells
where do NK cells come from?
bone marrow cell -> null cell (large, granular lymphocyte)-> NK cell
what does a null cell lack?
- T cell receptor (TCR)
- CD4 and CD8 co-receptors
do NK cells require interaction with an antigen-presenting cell to be activated?
no - part of innate immune system
-recognize virus infected cells and cancer cells
how can NK cells participate in adaptive immune response?
by participating in antibody-dependent cell mediated cytotoxicity (ADCC) - will recognize antibody on a pathogen infected cell and lyse cell
function of antigen presenting cells
surveillance cells - internalize antigens by phagocytosis and break them down to peptide fragments which are bound to MHC molecules -> peptide-MHC complex exposed on surface for presentation to T cells
2 types of MHC and which cells have each?
MHC I: all nucleated cells
MHC II: antigen presenting cells, endothelial cells, thymic epithelial reticular cells
name other cells (from different locations) that are antigen presenting cells
- cells in macrophage lineage
- Kupffer cells (liver)
- Langerhans cells (skin)
- dendritic cells (peripheral lymphoid organs)
- glial cells in CNS
- fibroblasts
- mast cells
peripheral lymphoid organs
- spleen
- lymph nodes/nodules
- tonsils
- appendix
- peyer’s patches (ileum)
subepithelial/diffuse lymphoid tissue
- lymphocytes free in loose CT
- diffuse infiltration in intestinal and respiratory tract, part of genitourinary system
- may be lymphoid nodules
capsules of lymphoid nodules
don’t have one
where/how can you find lymphoid nodules?
- may be in subepithelium
- solitary or aggregated (peyer’s patches)
composition of lymph nodes
dense lymphatic tissue surrounded by dense irregular CT capsule w/ trabeculae through node that converge on hilus
lymph node hilus
region where lymph exits node via efferent lymphatic vessels - arteries/veins also enter/leave node here
what constitutes stroma of node?
capsule and trabeculae + network of reticular fibers and cells
how are sinuses separated from capsule, trabeculae and dense lymphoid tissue?
by squamous endothelial cells + reticular cells + fixed macrophages attached to reticular fiber network
what antigen presenting cells are found in lymph node cortex?
large follicular dendritic cells (FDC)
types of lymphoid nodules in outer cortex of node
- primary - unstimulated (no germinal center)
- secondary - germinal center present
what do germinal centers contain?
- larger lymphoblasts
- marginal zone of smaller lymphocytes and some macrophages around periphery
when do germinal centers occur in lymphoid nodules?
when B cells activated by helper T cells undergo clonal expansion (lymphoblasts) towards becoming an antibody secreting plasma cell
describe the selection process that occurs w/ maturing B cell lymphoblasts
mature cells contact FDCs, which present antigens to them: -those w/ low affinity antibodies undergo apoptosis and are phagocytosed by macrophages
-cells w/ high affinity antibodies move to medullary cords and become plasma cells
what type of cells accumulate in mantle zone of lymphoid follicle?
cells that are non-specific for antigens presented by FDC
which parts of lymph nodes are primarily B cells and which are primarily T cells?
B cells: nodules and medullary cords
T cells: paranodular and inner cortex regions
medullary cords have high numbers of which cells?
plasma cells
segregation of B and T cells w/i nodules is based on what?
various cytokine signals
what empties into a subcapsular sinus and where are these located?
subcapsular sinus = b/w capsule and outer cortex
multiple afferent lymphatic vessels empty into it
where does lymph flow from subcapsular sinus?
into intermediate/trabecular sinuses that run along trabeculae -> medullary sinuses around medullary cords
importance of high endothelial venules
important route of lymphocyte migration (selectins on lymphocyte membrane aids recognition of HEV) - most lymphocytes enter node via this route
where are high endothelial venules found?
in paracortical zone
lining of high endothelial venules
tall cuboidal endothelial cells
pathway of lymphatic flow from origination back to venous system
- thymus -> T cells and bone marrow -> B cells into blood circulation
- migration through high endothelial venules into lymph node
- move into lymph node tissues and/or circulate out into lymphatic circulation
- return to blood via main thoracic duct
which cells recirculate into venous circulation?
- primarily T cells
- some B cells recirculate, but more stay in tissues compared to T’s
three tonsils?
- lingual
- pharyngeal
- palatine
lingual tonsils
diffuse infiltration of lymphocytes or multiple small nodules below epithelium of the posterior third of tongue
pharyngeal tonsils
adenoids
-posterior wall of nasopharynx
pharyngeal tonsil epithelium
covered w/ ciliated pseudostratified columnar epithelium - some portions may be stratified squamous (especially in old folks)
palatine tonsils
b/w glossopalatine and pharyngopalatine arches
palatine tonsil epithelium
stratified squamous epithelium - HAS DEEP CRYPTS (invaginations down into parenchyma)
capsule of palatine tonsil?
base and sides enclosed in dense CT capsule
peyer’s patches
aggregated nodules of lymphoid tissue located primarily in lower ileum
segregation of B and T cells in peyer’s patches
similar to lymph nodes:
- nodules mainly B cells
- paranodular area mainly T cells
what does the follicular epithelium of peyer’s patches contain?
M cells
appendix lamina propria
extremely rich in diffusely scattered lymphoid elements and solitary nodules
lymphadenitis
excessive immune response to infectious agents that results in proliferation of cells and edema in nodes - also causes inflammation
what are lymph nodes a common site of, clinically?
metastasis of cancer cells
why are lymphoid cells the source of various types of lymphoma?
b/c of the frequent, rapid division and differentiation of lymphoid cells
what is the primary mediator of graft rejection and GVHD?
T cells - by MHC antigens on cells
what does it mean when a graft is rejected?
patient’s immune system sees graft as foreign and attacks it
what does it mean when you have graft vs. host?
T cells in a graft can see the host as foreign and attack the host
in what procedure is GVHD a problem?
bone marrow transplants
can you still get GVHD even when MHC antigens are matched up in a transplant? why or why not?
yes - due to minor histocompatibility antigens
two examples of minor histocompatibility antigen mismatches
- H-Y- antigen present in male but not female tissue
2. HA-2 antigen associated w/ myosin
