Lymphoid Tissues Flashcards
Primary lymphoid tissue
generation of mature, but antigen naive, T and cells
development of antigen recognition
involve rearrangement of antigen receptor genes
ex) bone marrow and thymus
Secondary lymphoid tissue
naive lymphocytes reside while waiting to be activated
funnel antigen to antigen specific B and T lymphocytes to drive antigen dependent activation to effector and memory cells
ex) lymph nodes, tonsils, peyer’s patches, spleen
Tertiary lymphoid tissue
where elimination of antigen occurs
the battlefield
typically, the tissues have direct contact with external environment
ex) skin, GI tract, lungs, vagina
Bone Marrow
has pluripotent stem cells
has stroma
B lymphocyte development
earliest B cell precursors located near inner surface of bone, more mature cells are in the axis
immature to mature B cells can take place in secondary lymphoid organs
Pluripotent stem cells
differentiate into rbs, lymphocytes, granulocytes, platelets, monocytes
stroma
reticular stromal cells, macrophages, adipocytes
provide cell-to-cell contact plus soluble factors
thymocytes
differentiate into mature T cells
T lymphocyte maturation
originate in bone marrow, but mature in thymus
autoreactive T cells are deleted
mature T cells released into periphery to populate secondary lymphoid tissue
vast majority get killed off
thymus
bilaterally symmetrical lobes
after puberty it atrophies
thymocytes migrate from cortex to medulla over several days
subcapsular zone of thymus
outside cortex, entrance of prothymocytes
hassal’s corpuscles
thymocyte graveyards
do T cells undergo apoptosis or necrosis
apoptosis
Cortical epithelial cells
provide cell-to-cell contact, cytokines, and peptide hormones
Where are lymph nodes located
axillary, inguinal, and cervical regions, and intestinal mesentery
Lymphatic vessels
one way valves, giving them uni-directional flow
afferent lymphatics
feed lymph nodes
efferent lymphatics
transport lymph and cells until convergence with thoracic duct
thoracic duct
empties into left subclavian vein
primary follicles in cortex of lymph nodes
has resting B cells
secondary follicles in cortex of lymph nodes
has antigen-activating B cells
germinal centers of cortex of lymph nodes
has proliferating B cells
T cell-rich area (paracortex) of lymph nodes houses what
T helper cells
Where are dendritic cells located in the lymph node
T cell rich areas
Where are macrophages located in the lymph node
marginal sinus and medullary cords
what happens to the lymph node if there is little antigen stimulation
few primary follicles and no secondary follicles
What happens to the lymph node if there is a lot of antigen stimulation
lots of secondary follilces and may enlarge enough to be palpable
high endothelial venules
allow lymphocytes to enter lymph node from the blood
How do B cell travel through the lymph node
percolate through T cell rich areas, enhancing the probability that an antigen specific B cell will interact with an antigen specific T cell
Spleen
responsible for blood-borne antigens
largest lymphoid tissue
no high endothelial cenules, but has analogous tissue
Functions of spleen
remove particulate matter and senescent red blood cells from circulation (in red pulp) and expose lymphocytes to antigens (in white pulp)
Peyer’s patches
localized in terminal ileum
B cell follicles surrounded by zone rich in T cells
M cells transport proteins and microbes from intestinal lumen
M cells
microfolds on luminal surface
Langerhans cells in the skin
sample the environment, can’t activate T cells
Langerhans cells
immature dendritic cells present in epidermis
capture and transport antigen to nearest lymph nodes
act as antigen presenting cells to activate T cells
langerhans cells in lymph node
mature, can’t ingest, but will activate T cells
immune response in a lymph node
antigen transport from tissues to a lymph node
B-cell activation
Germinal center B cells differentiate to plasma cells creating a high affinity antibody
Lymphocyte homing
some lymphocytes have a preferred home
dependent on specific “addressins”
Lymphocyte recirculation
travel between lymphoid organs
greater probability that rare lymphocytes become activated
recirculation is critical for dispersal of naive and memory cell populations
an individual naive lymphocyte may make a complete circuit 1-2 times a day
Memory lymphocytes
have different migration pattern than naive cells
often found in peripheral blood
