Histology - Immune

Front 1

Explain the division of the lymphoid organs in central and peripheral

Back 1

Central: Origin and main differentiation of the cells.
Peripheral: Proliferation, additional differentiation and immune response executed.

Front 2

1.What are the central lymphoid organs?

Back 2

Include the thymus, and the bone marrow and the gut-associated lymphoid tissue (GALT) [if we accept these as the only equivalents of the bursa of Fabricius].

Front 3

1.What are the peripheral lymphoid organs?

Back 3

spleen, the lymphoid nodes, the solitary nodule, the tonsils, the appendix, the Peyer patches.

Front 4

1.What are the encapsulated lymphoid organs?

Back 4

thymus, lymph nodes and spleen

Front 5

1.What are the uncapsulated lymphoid organs?

Back 5

diffuse and tonsils

Front 6

1.What is the proportional contribution of the different lymphoid organs to the total lymphoid mass?

Back 6

Spleen, lymph nodes and thymus make ~ 12 % of lymphoid mass; MALT (mucous associated lymphoid tissue) = BALT (bronchus associated lymphoid tissue) plus GALT (gut associated lymphoid tissue) make ~ 83 % of lymphoid mass

Front 7

1.What is the immune response?

Back 7

Has a cellular and humoral (antibodies components) and it is defined as the response the immune systems sets up when it faces an antigen.

Front 8

1.What is an antibody and what is the importance of its variable portion?

Back 8

Glycoproteins that interact with antigens. They have a variable portion with infinite possibilities for antigen fixation.

Front 9

1.Describe the overall pathways of differentiation of the B cells.

Back 9

Their main differentiation takes place in the bone marrow and the GALT. When they are activated, they become plasma cells or B memory cells.

Front 10

1.What is a immunoblast?

Back 10

Transient stage for a stimulated B lymphocyte. It is quite a big cell, with prominent nucleolus and basophilic cytoplasm.

Front 11

1.What is the differentiation pathway for the T cells?

Back 11

Main differentiation in the thymus

Front 12

1.What are the four types of T cells and what are their function?

Back 12

Helper cells: Help with the differentiation of B cells into plasma cells.
Suppressor: Suppress the production of antibodies.
Cytotoxic: Similar to natural killer cells.
Gamma/delta: migrate and remain within epithelia (skin, oral mucosa, intestine, vagina) and encounter antigens before they enter the body.
T memory cells: React quickly to an antigen previously faced.

Front 13

1.What are the natural killer cells, what are their functions and how do they perform them?

Back 13

Subpopulation of N cells. The cell does not participate in typical immune response. They recognize tumor and virus infected cells and destroy them with perforin (cytolysin) and granzymes (fragmentins) which target the damaged cell membrane. To avoid self-destruction, it secretes protectin.

Front 14

1.What are the antigen presenting cells?

Back 14

Phagocyte and process antigens, retain the products in the membrane for a long time, and when needed they present the processed antigen to the T helper lymphocyte. They are part of the mononuclear phagocyte system (MPS), once called reticuloendothelial system (RES): Regular macrophages, the special ones at certain locations (microglia at the central nervous system, dust cells in the lungs, etc), the Langerhans cells and their mature form, the dendritic cells, and some of the epithelioreticular cells of the thymus.

Front 15

1.Define the general features of the thymus.

Back 15

Encapsulated lymphoepithelial organ divided in lobules, with a clear separation between its cortex and its medulla (corticomedullar pattern).

Its major development is after birth, reaching a maximum size around the 10th year of life. The involution starts after puberty but never disappears.

Front 16

1.What cells are found in the cortex of the thymus?

Back 16

Epithelioreticular cells (type I, II and III), small lymphocytes.

Front 17

1.What cells are found in the medulla of the thymus?

Back 17

Epithelioreticular cells (type IV, V and VI), Hassall’s corpuscles (key feature of the organ), and large and medium lymphocytes.

Front 18

1.What are the epithelioreticular cells?

Back 18

Pale eosinophilic, star-shaped cells with prominent nucleus that act as reticular fibres in the thymus.
Cortical (I-III) and medullar (IV-VI) types
Contribute to the blood-thymus barrier (type I)
Antigen-presenting capabilities (type II and III)
Secretion that attract and differentiate lymphocytes into T lymphocytes.
When type VI cells get old, they create the Hassall’s corpuscle.

Front 19

1.What is the Hassall’s corpuscle and where is it found?

Back 19

Hassall’s corpuscles aid in the maturation of the dendritic cells. Medulla of the Thymus

Front 20

1.Characterize the components, location and importance of the blood-thymus barrier.

Back 20

Prevents premature exposure of lymphocytes to antigen (to inhibit tolerance)

Non-fenestrated endothelium with occluding juctions (major component of the barrier)
Thick basal lamina
Pericytes
Macrophages
Type I epithelioreticular cells

There is not blood-thymus barrier in the medulla.

Front 21

1.What is the positive and negative selection of the lymphocytes?

Back 21

Positive selection: Lymphocytes that mildly or moderately react to antigens survive
Negative selection: The ones that strongly react are eliminated

Front 22

1.What are the T dependent zones of the lymphoid organs?

Back 22

Paracortical zones of lymph nodes, portions of the Peyer patches in the ileum and the periarterial sheaths of the white pulp of spleen.

Front 23

1.How can we differentiate a secondary from a primary lymph nodule?

Back 23

Spherical aggregates of cells at lymph nodes cortex, spleen and other organs.
Primary: Accumulation of lymphocytes
Secondary: Corona, mantle (maturation zone) and a germinal centre.

Front 24

1.What are the functions of the lymph nodes?

Back 24

400 – 450 encapsulated, spherical or kidney-shaped organs good for cell proliferation and also as in-line filters along the course of lymphatic vessels. They are divided into capsule, outer and inner cortex, medulla.

Front 25

1.Describe the portions of the lymph nodes.

Back 25

Outer cortex, Inner cortex, medulla

Front 26

1.What are the main features of both outer and inner cortices?

Back 26

Subcapsular sinus: Lined by macrophages and reticular cells.
Lymphoid tissue: Related to the network of reticular cells and fibres.
Lymphoid nodules: in their germinal centres we find follicular dendritic cells that can keep yet not actively present antigen-antibody complexes.
Capsular trabeculae: Connective tissue derived from the capsule.
Intermediate sinuses: Communicate subcapsular sinuses with medullar ones
Inner cortex is a continuation of outer cortex, usually without nodules in the healthy status.

Front 27

1.What is the importance of the high endothelial venules?

Back 27

Recirculation, Lymphocytes can return to lymph nodes. he recirculation allows spreading information about antigens for a better immune response

Front 28

1.What are the functions of the spleen?

Back 28

Aside of allowing the proliferation of lymphocytes, it destroys most of the old and abnormal RBCs and also the platelets. It is also the main site of extramedullary hematopoiesis if needed.

Front 29

1.What are the components of the spleen?

Back 29

Capsule and trabeculae
White pulp:
Maginal zone:
Red pulp:

Front 30

1.What structure characterizes the lymph nodules of the spleen?

Back 30

White Pulp

Front 31

1.What is the red pulp?

Back 31

Splenic cords (Billroth’s cords) and sinusoids.

Front 32

1.What is the unencapsulated lymphoid tissue?

Back 32

Lymphatic nodules isolated or aggregated at the lamina propria of digestive, respiratory and urinary tract organs. Examples are the isolated nodules, the
Peyer patches of the ileum and the appendix.

Front 33

1.What are the tonsils that are usually the target of pathogens?

Back 33

Palatine

Front 34

1.What are the tonsils that cause chronic respiratory obstructive symptoms?

Back 34

Pharyngeal also known as adenoid