2-Lymphoid Tissue

Question 1

primary lymphoid tissue

Answer 1

-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

Question 2

secondary lymphoid tissues

Answer 2

-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

Question 3

tertiary lymphoid tissue

Answer 3

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

Question 4

bone marrow

Answer 4

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

Question 5

B lymphocyte development

Answer 5

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

Question 6

T lymphocyte development

Answer 6

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

Question 7

thymus

Answer 7

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

Question 8

thymus structure

Answer 8

-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

Question 9

cortical epithelial cells

Answer 9

act as thymic nurse cells for cell to cell contact, cytokines (IL1, IL3, IL6, IL7), peptide hormones

Question 10

peptide hormones

Answer 10

thymulin
thymosin
thymopoietin

Question 11

lymph nodes

Answer 11

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

Question 12

lymph node locations

Answer 12

axillary
inguinal
cervical regions
intestinal mesentary

all fed by one or more afferent lymphatics > efferent lymphatics transport lymph to thoracic duct > subclavian V

Question 13

lymph node components

Answer 13

1. lymph empties into subcapsular sinus
2. flows past immune system cells in cortex to medulla
3. B cell rich areas/follicles
4. T cell rich area/paracortex with T helper cells and dendritic cells
5. macrophages in marginal sinus and medullary cords

Question 14

B cell rich areas/follicles

Answer 14

-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

Question 15

high endothelial venules

Answer 15

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

Question 16

spleen

Answer 16

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

Question 17

white pulp

Answer 17

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

Question 18

MALT

mucosa associated lymphoid tissue

Answer 18

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

Question 19

peyer’s patches

Answer 19

@ 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

Question 20

langerhan cells

Answer 20

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

Question 21

immune response in lymph node

Answer 21

1. 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
2. B cells @ germ center diff into plasma cells with high anti affinity
3. drain lymph enriched with antibody
4. travel to bone marrow for antibody production

Question 22

lymphocyte homing

Answer 22

locate preferentially in specific lymphoid organs or tissues
-dependent on addressins that get a cell back into preferred tissue

Question 23

lymphocyte recirculation

Answer 23

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

Question 24

memory cell recirculation

Answer 24

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