10b – Organs of the Immune System

Question 1

Primary lymphoid organs:

Answer 1

-thymus
-bone marrow
-Bursa fabricus (birds)
-Illeal Peyer’s patches
-lymphoglandular complexes

Question 2

Function of primary lymphoid organs:

Answer 2

-sites where lymphocytes develop

Question 3

Thymus location:

Answer 3

-in thoracic cavity, near the heart
>can extend into neck region

Question 4

Thymus size:

Answer 4

-greatest in newborn
-slowly decreases towards adulthood

Question 5

Thymus structure:

Answer 5

-lobules of loosely packed epithelial cells
>each covered by connective tissue capsule
>outer cortex, inner medulla

Question 6

Outer cortex of thymus:

Answer 6

-outer part of the lobule
-densely packed with lymphocytes and epithelial cells

Question 7

Inner medulla of thymus:

Answer 7

-fewer lymphocytes and fewer epithelial cells
-Hassall’s corpuscle

Question 8

Hassall’s corpuscle:

Answer 8

-structure in medulla
-contains blood vessel, but walls are very thick preventing antigen to enter the thymus

Question 9

Thymus function:

Answer 9

-no lymphatics leaving the thymus
*source of thymus-derived lymphocytes (T cells)
>positive and negative selection

Question 10

What would happen if you removed the thymus?

Answer 10

-the animal would die because of lack of adaptive immunity

Question 11

Young adult moose thymus:

Answer 11

-has 10^8 thymocytes
-5x10^7 new cells are generated each day
>only about 10^6 leave the thymus each day as mature T cells
>*2-4%

Question 12

Bursa fabricius:

Answer 12

-found only in birds
-round sac above the cloaca
-large in young birds, decreases in size

Question 13

Bursa fabricius structure:

Answer 13

-similar to other lymphoid tissue
-lymphocytes embedded in epithelial tissue

Question 14

Epithelial tissue of bursa fabricius:

Answer 14

-lines a hollow sac connected via a duct to the cloaca

Question 15

Follicles of bursa fabricius:

Answer 15

-inside the sac fold of epithelium that extend into lumen
-each contain lymphocytes
-divided into cortex and medulla

Question 16

Function of bursa fabricius:

Answer 16

-source for B cells in birds
-also traps foreign antigen (not typical for primary lymphoid organs)

Question 17

Peyer’s patches:

Answer 17

-located in wall of the intestine
1. Ileal patches
2. Jejunal

Question 18

When do the Peyer’s patches develop?

Answer 18

-in most domestic species, develop before birth
-primates, rabbits and rodents, develop after birth in response to microbiota

Question 19

Ileal patches:

Answer 19

-site of lymphocyte development (primary lymphoid organ)
-one continuous patch
-largest shortly before birth
-B cell development

Question 20

Jejunal patches:

Answer 20

-inductive site
-distinct patches
-antigen uptake and induction of immunity

Question 21

Inductive site (jejunal patches):

Answer 21

-filtration of lymph
-antigen presentation
-activation of naïve lymphocytes
-clonal expansion

Question 22

Secondary lymphoid organs:

Answer 22

-lymph nodes
-spleen
-tonsils
-Jejunal Peyer’s patches
-other lymphoid tissues

Question 23

Function of secondary lymph organs:

Answer 23

-filter the lymph
-site of antigen-presentation
-activation of lymphocytes
-differentiation and maturation of Ag-specific cells

Question 24

Lymph nodes:

Answer 24

-filters for free antigens and sites for antigen presentation
-structure similar in most species (except pigs)
-birds don’t have them
-lymph flows through afferent and efferent lymph

Question 25

Leukocytes enter lymph nodes via:

Answer 25

-HEVs
-lymph

Question 26

Arrangement of lymph nodes:

Answer 26

-paracortex: T cells
-cortex (in follicles): B cells
>follicular dendritic cells (residential)

Question 27

Residential cells in lymph nodes:

Answer 27

-network of dendritic cells and follicular T helper cells

Question 28

Germinal centers of lymph node:

Answer 28

-areas where B cells start to mature
>B cells
>T helper cells
>APC
>follicular dendritic cells
*where somatic hypermutation occurs

Question 29

Endothelial cells in a lymph node:

Answer 29

-in the medulla
-also some vessels in the T cell zone and the follicular dendritic cell network in the B cell follicle

Question 30

Structure of tonsils and Peyer’s patches:

Answer 30

-similar
-found at mucosal sites
-covered by one layer of epithelial cells
>lots of immune cells beneath it

Question 31

Immune cells in tonsils and Peyer’s patches:

Answer 31

-dome regions
-follicles
-T cells

Question 32

Dome region, tonsils:

Answer 32

-macrophages
-dendritic cells

Question 33

Follicles, tonsils:

Answer 33

-B cells
-follicular dendritic cells
-Th cells on the edge

Question 34

T cells, tonsils:

Answer 34

-interfollicular region

Question 35

Function of tonsils and Peyer’s patches:

Answer 35

-antigen is trapped or taken up by M-cells
-APCs present it to T cells (3 signals) in the interfollicular region
-follicular dendritic cells ‘hold it’ for B cells

Question 36

Follicular dendritic cells ‘hold antigen’ for the B cells:

Answer 36

-form a network of dendritic cells
-when antigen is filter, they grab it and hold it out for B cells to recognize and bind to it I if BCR is specific for it
*not presented via MHC

Question 37

Spleen functions:

Answer 37

-‘filter’ for the blood
-storage of RBCs and platelets

Question 38

Areas in spleen:

Answer 38

-red pulp
-white pulp
*separated by a marginal zone

Question 39

Marginal zone in spleen:

Answer 39

-rich of APCs

Question 40

Red pulp:

Answer 40

-filtering and storage of RBCs

Question 41

White pulp:

Answer 41

-WBCs (T and B cell rich)
*incoming arterioles are surrounded by lymphoid tissues (mainly T cells)
>B cells are in follicles scattered around the lymphoid tissues

Question 42

How do blood cells enter the spleen?

Answer 42

-enter via arterioles
-flow through marginal zones to ensure that blood antigens are trapped

Question 43

Tertiary lymphoid ‘organs’:

Answer 43

-mucosa and skin associated lymphoid tissue