Lymphoid Tissues and Leukocytes

Question 1

List the types of leukocytes in the vertebrate immune system.

Answer 1

1. Lymphocytes
2. Eosinophils
3. Neutrophils
4. Monocytes
5. Basophils

Question 2

What is the function of neutrophils?

Answer 2

1. Most abundant type of WBC and first responder to microbial infection
2. Unable to renew their lysosomes and die after having phagocytosed a few pathogens (forms the majority of pus)

Question 3

What is the function of eosinophils?

Answer 3

1. Prominent at the sites of allergic reactions and parasitic infections (rare in blood but common at mucous membranes)
2. Do not phagocytose pathogens but instead release chemical products which perforate cell membranes
3. Function as the primary response to large multicellular parasites

Question 4

What is the function of basophils?

Answer 4

1. Chiefly responsible for initiating inflammatory responses by releasing the chemicals histamine and heparin
2. Functionally similar to mast cells, however they circulate in the bloodstream whereas mast cells are localized
3. Because they promote inflammation, they are common contributors to allergic responses

Question 5

What is the function of monocytes?

Answer 5

1. Largest type of leukocyte and share phagocytosis duties with neutrophils
2. Slower to respond than neutrophils but are longer lasting, as they can renew their lysosomes for continued digestion
3. Differentiates into two types of cells in response to pathogenic infection - macrophages and dendritic cells
4. Macrophages will remain in the tissue and phagocytose whereas dendritic cells present antigen fragments to lymphocytes

Question 6

What is the function of lymphocytes? Where are they found?

Answer 6

Function:
1. Responsible for the production of Ab which target specific Ag present on pathogens
2. Lymphocytes are also involved in the destruction of virus-infected body cells (via cytotoxic T cells and NK cells)
3. Lymphocytes include B cells (which become Ab-secreting plasma cells) and T cells (which mediate B cell activity)

Located:
More common in the lymphatic system than blood and are slowest to respond (requiring Ag presentation)

Question 7

What are the primary lymphoid organs?

Answer 7

1. Thymus
2. Red bone marrow

Question 8

What are the secondary lymphoid organs?

Answer 8

1. Neck (cervical) lymph nodes
2. Armpit (axillary) lymph nodes
3. Spleen
4. Peyer’s patches
5. Groin (inguinal) lymph node

Question 9

Where are blood and immune cells produced?

Answer 9

Red bone marrow during a process called hematopoiesis

Question 10

What is the function of the thymus?

Answer 10

Secretes hormones that are essential for normal immune function and develops T-lymphocytes

Question 11

What is the function of the spleen?

Answer 11

1. Filters foreign substances and Ab-complexed pathogens from the blood
2. Houses B and T cells, macrophages, dendritic cells and NK cells
3. Ab are synthesized and secreted by activated plasma cells in the spleen

Question 12

What are the functions of the lymph nodes?

Answer 12

1. Filter out antigens in the lymph before being returned to circulation
2. Houses large populations of T and B cells, dendritic cells and macrophages

Question 13

How do cells of the immune system travel between lymphatic and blood circulatory systems?

Answer 13

Extravasation (passing through to surrounding tissue)

Question 14

What stimulates stem cells to differentiate into immune cells?

Answer 14

Cytokines

Question 15

Where do the lymphocytes mature?

Answer 15

Primary lymphoid tissues

Question 16

After maturation, where do T and B lymphocytes circulate to?

Answer 16

Secondary lymphoid tissues

Question 17

What is MALT?

Answer 17

Mucosa-associated lymphoid tissue (MALT) forms the mucosal immunity which functions independently of the systemic immune system, and has its own innate and adaptive components.

Question 18

What is MALT made out of?

Answer 18

Collection of lymphatic tissue that combines with epithelial tissue lining the mucosa throughout the body.

Question 19

What is the function of MALT?

Answer 19

Functions as the immune barrier and response in areas of the body with direct contact to the external environment

Question 20

Why is MALT important?

Answer 20

Mucosal surfaces, such as the nasal passages, are the first tissues onto which inhaled or ingested pathogens are deposited.

Question 21

What does the mucosal tissue include?

Answer 21

1. Mouth
2. Pharynx
3. Esophagus
4. GI
5. Respiratory
6. Urogenital

Question 22

What happens when foreign particles enter MALT?

Answer 22

1. Taken up by absorptive epithelial cells called M cells and delivered to APCs located directly below the mucosal tissue
2. Processed Ag displayed on APCs are detected by T cells in the MALT and at various mucosal induction sites
3. Activated T cells then migrate through the lymphatic system and into the circulatory system to mucosal sites of infection

Question 23

Where are M cells located?

Answer 23

Peyer’s patch, a lymphoid nodule (with diffused boundaries, no encapsulation)

Question 24

What are the APCs of the mucosal immune system?

Answer 24

Primarily - Dendritic cells

B cells and macrophages - minor roles

Question 25

Processed Ag displayed on APCs are detected by T cells in the MALT and at various mucosal induction sites, such as?

Answer 25

• Tonsils
• Adenoids
• Appendix
• Mesenteric lymph nodes of the intestine