2-Lymphoid Tissue Flashcards
primary lymphoid tissue
-generation of mature, antigen naive T and B cells
-devel of antigen recog
-involves rearrangement of antigen receptor genes
i.e. bone marrow and thymus
secondary lymphoid tissues
-where naive lymphs reside while waiting to be activating
-funnel antigen to antigen specific B and T lymphs to drive antigen dependent activation to effector and memory cells
i.e. lymph nodes, tonsils, peyer’s patches, spleen
tertiary lymphoid tissue
where elimination of antigen occurs
-aka battlefield where immune system defends tissues from microbes
-tissues have direct contact w/ external environ
-majority of B and T cells here are memory cells
i.e. skin, GI, lungs, vagina, mucosa
bone marrow
has pluripotent stem cells > diff into RBC, lymphs, granulocytes, erythrocytes, platelets, monocytes
primarily long bones, sternum, pelvis
stroma- reticular stromal cells, macros, adipocytes, provide cell to cell contact + soluble factors
B lymphocyte development
earliest B cell precursors near inner surface of bone > mature in central axis of marrow cavity
maturation in 2nd lymph tissue
autoreactive B cells deleted @immature stage
T lymphocyte development
og @ bone marrow as stem cells>prothymocytes
move to thymus as ‘thymocytes’ then maturate > released into periphery to populate 2nd lymph tissue
autoreactive are deleted
thymus
pyramid shape organ in upper anterior thorax
-has bilaterally symmetric lobes divided into lobules with cortex and medulla
atrophies after puberty and is gone by middle age
T cell immunity maintained by long lived memory cells
thymus structure
-outside cortex is subcapsular zone and entrance of prothymocytes
-migrate to medulla as mature T lymphs expressing TCR, CD3, and either CD4/8
-hassall’s corpuscles like thymocyte graveyards, undergo apoptosis
cortical epithelial cells
act as thymic nurse cells for cell to cell contact, cytokines (IL1, IL3, IL6, IL7), peptide hormones
peptide hormones
thymulin
thymosin
thymopoietin
lymph nodes
house immune system cells and main responders to tissue borne antigens
plasma fluid thru capillaries into tissue returned to blood by draining ‘lymph’
-antigens are flushed thru lymph nodes
one way valves so uni-directional flow
lymph node locations
axillary
inguinal
cervical regions
intestinal mesentary
all fed by one or more afferent lymphatics > efferent lymphatics transport lymph to thoracic duct > subclavian V
lymph node components
- lymph empties into subcapsular sinus
- flows past immune system cells in cortex to medulla
- B cell rich areas/follicles
- T cell rich area/paracortex with T helper cells and dendritic cells
- macrophages in marginal sinus and medullary cords
B cell rich areas/follicles
-primary = resting B cells
-secondary = antigen activated B cells
-germinal centers = proliferating B cells
if little antigen stimulation then fewer primary follicles and no secondary
-a lot of antigen = numerous secondary follicles and may enlarge
high endothelial venules
allow lymphocytes to enter lymph node from the blood
-B cells will percolate thu T cell rich areas and enhance the probability that an antigen specific B cell will interact with T cell
spleen
immunologic organ for blood borne antigens
-largest lymphoid tissue
-removes particulate matter and senescent RBCs from circulation (in red pulp) and expose lymphocytes to antigens in white pulp
NO endothelial venules but analogous tissue
white pulp
distinct B and T cell rich zones
-splenic A > central A > penicilliary arterioles
PALS surround central A and penicilliary arterioles, T cell rich
B cell rich follicles are extensions of PALS
MALT
mucosa associated lymphoid tissue
exposes immune system to antigens across mucosal epithelia bc most pathogens encounter @ lungs, GI tract, GU tract
-GI has intraepithelial lymphocytes, M cells, Peyer’s patches
antigen transport occurs across the mucosal epithelium rather than afferent lymph
peyer’s patches
@ terminal ileum = small intestine secondary MALT
-B cell follicles surrounded by zone rich in T cells
-HEVs transport lymphocyte into patches
-M ‘microfolds’ cells transport proteins and microbes from lumen
langerhan cells
aka immature dendritic cells in epidermis capture and transport antigen to nearest lymph node so like antigen presenting cells to activate T cells
@ skin they sample environ, can’t actually activate T cells > proinflamm cytokines retract dendritic processes so lose adhesiveness and migrate into lymph channels
mature in lymph node and activate T cell, can’t ingest
immune response in lymph node
- B cells will activate, prolif, differentiate into plasmablast
-some plasmablasts go to medullary cords and produce low affinity antibody
-others migrate to B cell rich areas form germinal center - B cells @ germ center diff into plasma cells with high anti affinity
- drain lymph enriched with antibody
- travel to bone marrow for antibody production
lymphocyte homing
locate preferentially in specific lymphoid organs or tissues
-dependent on addressins that get a cell back into preferred tissue
lymphocyte recirculation
travel b/t lymphoid organs so greater probability for rare lymphocytes to become activated
-critical for dispersal of naive and memory cell pops
-a naive lymph may complete circuit 1-2 times/day
memory cell recirculation
many lymphocyte in peripheral blood are memory cells
-traffic to 3 lymphoid tissues @ skin or intestinal lamina propria
-mucosal antigens that elicit secretory IgA and IgA secreting plasma cells distributed to mucosal epithelia but not optimally effective if IgA resp in lymph node or skin