6.5.2 Cells and tissues of the immune system

Question 1

What are the different types of WBCs?

Answer 1

Granulocytes:
Eosinophil.
Basophil.
Neutrophil

Mononuclear cells:
Lymphocytes.
Monocyte

Question 2

Which 2 cells are involved in the phagocytosis (ingestion) of bacteria?

Answer 2

Neutrophils (granulocytes)

Macrophage (evolves from circulating monocytes) [mononuclear cells]

Question 3

Which 2 cells are involved in the destruction of parasites?

Answer 3

Eosinophils (found in the circulation).

Basophils (tissue mast cells, found under epithelial surfaces).

Question 4

What cell is involved in the immunity the viruses?

Answer 4

Lymphocytes (mononuclear cell)

Question 5

Lymphocytes are supported by what?

Answer 5

Lymphoid tissues

Question 6

What are the 2 types of lymphoid tissues/organs?

Answer 6

Primary Lymphoid Organs:
Bone marrow, Thymus

Secondary Lymphoid Organs:
Lymph nodes, Spleen, Mucosal associated lymphoid tissues -MALT (e.g. Peyer’s patches)

Question 7

What is the difference between primary and secondary lymphoid organs?

Answer 7

Primary organs are there for lymphocyte development

Secondary organs are involved in the response to infection

Question 8

Where are B cells of the lymphocytes developed?

Answer 8

They remain in the bone marrow

Question 9

Where are T cells of the lymphocytes developed?

Answer 9

They must leave the bone marrow and go to the thymus to be ‘educated’

Question 10

What is the thymus?

Answer 10

The site of T cell development.

Question 11

Explain the histology of the thymus:

Answer 11

Has lobes.

Has a darker outer cortex.

Has a lighter inner medulla.

T cells enter via the peripheral capsule and make their way to the medulla until they meet a blood vessel where they can escape

Question 12

What 2 ‘decisions’ do T cells have to make in the thymus?

Answer 12

1- Each T cell must generate a unique antigen receptor (TCR)

2- Each T cell must decide whether to become a CD4+ or CD8+ cell

Question 13

What is Thymic lymphoma (cats)?

Answer 13

Neoplasia of thymic lymphocytes.

Associated with FeLV infection.

Clinical signs: anorexia, weight loss, dyspnoea

Question 14

What is Bursa of Fabricius?

Answer 14

Found in birds.

Referred to as “Cloacal tonsil”.

Is the bird’s primary lymphoid organ for maturation and differentiation of B cells.

Question 15

What are lymph nodes?

Answer 15

Scattered strategically all around the body.

Function to protect certain areas of the body

Question 16

Explain the lymph node structure:

Answer 16

Kidney shaped, filters lymph

Lymph enters via afferent lymphatic vessels and leaves via efferent lymphatic vessels

Inner medulla with medullary chords

Arterial vessel (supply)
Venous vessel (drain)

Question 17

What are the separate T and B cell areas of a lymph node?

Answer 17

B cells migrate to the follicles.

T cells live and work in the surrounding tissue (the paracortex)

Question 18

What is the function of lymph nodes?

Answer 18

Filters tissue fluid (lymph) and traps foreign organisms/ antigens

environment for recognition of antigen

lymphocyte activation and differentiation

Question 19

List the 5 superficial lymph nodes that are palpated in a clinical exam.

Answer 19

Mary Poppins Anus Sells Pictures

Mandibular
Prescapular
Axiallary
Sub-inguinal
Popliteal

Question 20

What is the structure of the spleen?

Answer 20

Red pulp for haematological functions.

White pulp for immunological functions (acts as a filter for blood)

Question 21

What are the functions of the spleen?

Answer 21

Haematopoietic organ in foetal life

Removal of particulate material from bloodstream:
- foreign organisms
- old RBCs.

Immune responses to blood-borne pathogens.

Store of RBCs and platelets

Question 22

How is tissue fluid (lymph) produced and returned to the circulation?

Answer 22

Excess fluid produced and drained via lymphatic system to return to circulation.

Lymph nodes located near lymph

Question 23

What ducts drain what?

Answer 23

Thoracic duct drains body

Tracheal duct drains head

They join to empty into one large venous vessel cranial to the heart to return to plasma

Question 24

How do antigens enter lymph nodes? (2)

Answer 24

Free antigen swept in afferent lymph and is trapped

Antigen presenting cells eat antigen and then migrate via afferent lymph to LN paracortex

Question 25

What is the role of the dendritic cells?

Answer 25

• Differentiate from monocytes
• Immature DCs at epithelial surfaces eat antigens
• Migrate via afferent lymphatics to LN to process antigens before presenting to T cells
• Stay in LN paracortex to present to naive T cells

Question 26

What are high endothelial venules (HEVs)

Answer 26

• Instructs lymphocytes when its time to get off
• HEVS + lymphocyte = cell adhesion molecules so that the lymphocytes can attach and squeeze their way through the HEV area into the lymphoid tissues

Question 27

Following activation in the lymph node, what happens to the cells?

Answer 27

• Multiplication (thousands of clones)
• Differentiation (into a mature phenotype)
• B cells -> plasma cells (migrate from follicles to medullary cords to start producing antibodies)
• Activated T cells leave LN to search for infection

Question 28

What is the system, by which lymphocytes travel around various secondary organs?

Answer 28

Immune surveillance: