cells & tissues of the immune system

Question 1

primary lymphoid tissues

Answer 1

where immune cells originate and develop:

• bone marrow
• thymus (site of T cell maturation)

Question 2

secondary lymphoid tissues

Answer 2

where the immune response is activated:

• lymph nodes
• tonsils
• spleen
• mucosa-associated lymphoid tissue

Question 3

myeloid WBCs

Answer 3

• neutrophils
• eosinophils
• basophils and mast cells
• antigen-presenting cells (macrophages and dendritic cells)

* RBCs and platelets also come from myeloid precursors

Question 4

lymphoid WBCs

Answer 4

• B cells
• T cells
• NK cells

Question 5

Neutrophils

Answer 5

• primary cell of the innate immune system
• ingest and kill pathogens, produce myeloperoxidase, do not present antigen
• maturation: blast -> myelocyte -> band -> neutrophil
• release of granulocyte colony stimulating factor during infection leads to increased myeloid precursors in the peripheral blood as bone marror mobilizes neutrophils

Question 6

Answer 6

neutrophil

Question 7

Answer 7

eosinophil

bilobed nuclei, bright pink granules

Question 8

eosinophils

Answer 8

• innate immunity
• stimulated by IL-5
• increased in parasitic diseases and hypersensitivity
• attach to surface of nematode larvae by binding IgG and IgE produced by B cells (antibody dependent cell mediated cytotoxicity)
• not antigen presenting
• maturation: precursor -> myelocyte -> eosinophil

Question 9

Answer 9

basophil

(lots of dark granules)

Question 10

Answer 10

mast cell

Question 11

basophils and mast cells

Answer 11

• basophils in peripheral blood; mast cells in tissues
• key function = inflammation
• involved in anaphylaxis: receptors for Fc portion of IgE

release histamine and other cytokines

• innate immunity: TLRs on surface recognize PAMPs

Question 12

Answer 12

monocyte

Question 13

Answer 13

macrophage

Question 14

monocytes and macrophages

Answer 14

• monocytes circulate in blood; macrophages are activated in tissues
• innate immunity: phagocytosis of pathogens and debris; cytokine production
• produce IL-1, TNF, IL-12
• adaptive immunity: professional antigen presenting cells

Question 15

tissue resident macrophages

Answer 15

• alveolar mΦ (lung)
• kuppfer cells (liver)
• microglia (brain)
• red pulp mΦ (spleen)
• tingible body mΦ (germinal center)

Question 16

antigen presenting cells

Answer 16

• mΦ, dendritic cells, B cells
• link innate and adaptive immunity
• express pattern recognition receptors (TLRs) that bind PAMPs
• MHC class II on cell surface for antigen presentation:
  1. engulf pathogens
  2. digest proteins
  3. express peptides in MHC II

Question 17

dendritic cells

Answer 17

• antigen presenting cells
• finger like projections help present antigen
• induce T cell and primary antibody response: migrate to lymph nodes to present antigen to CD4+ T cells
• located under skin (langerhans cells) and in mucosa
• lineage: complicated…can be myeloid and lymphoid

Question 18

B cells

Answer 18

• adaptive immunity: involved in antibody-based humoral immunity
• CD19+ and CD20+
• differentiate into plasma cells that secrete antibodies
• maturation occurs in bone marrow: pro-B cell => pre-B cell => immature B cell

Question 19

Answer 19

lymphocyte

Question 20

Answer 20

plasma cell

pale area = golgi….very active protein synthesis for antibody production

Question 21

plasma cells

Answer 21

• come from B cells
• CD38 and CD138
• produce and secrete antibodies

Question 22

T cells

Answer 22

• majority of lymphocytes in circulation
• adaptive immunity
• cell mediated immunity: recognize protein antigens (presented by MHC) and kill virus infected cells, tumor cells, foreign cells
• originate in bone marrow and maturation occurs in thymus: CD3+ => CD4+ helper and CD8+ cytotoxic

Question 23

NK cells

Answer 23

• innate immunity
• directly kills infected cells and tumor cells:
  1. recognition of a cell’s lack of MHC class I
  2. binding
  3. secretion of cytotoxic granules
• CD56+ and CD16+
• do not express specific receptors

Question 24

lymphatic stroma (lymph nodes, nodules, and spleen)

Answer 24

• type III collagen reticular fibers produced by reticular cells
• loose connective tissue

Question 25

thymus stroma

Answer 25

- branching, interconnected **epithelioreticular cells** (6 types) - come from embryonic branchial pouch 3 - stroma, but also involved in T cell education: secrete interleukins, colony stimulating factor, and interferon to promote expression/deletion of CD antigens on T cell surfaces - types 2 + 5: present self and foreign antigens to T cells at an early stage =\> must recognize antigens to go from cortex to medulla and continue maturation - type IV forms **thymic (Hassall's) corpuscles**: large, pink staining, concentric curls of keratinized epithelioreticular cells that secrete interleukins

Question 26

lymph nodules

Answer 26

- **dense clumps of B cells** in a meshwork of reticular fibers - found in diffuse tissue of lymphatic organs or in loose connective tissue of GI, respiratory, and urinary tracts - not considered organs b/c no capsule - during immune response: **geminal center** stains lighter due to larger cells with more cytoplasm and euchromatin (due to replication)

Question 27

lymph nodes

Answer 27

- small organs along lymphatic vessels that "filter" lymph to increase change of antigens encountering mΦ's and lymphocytes - structure: - connective tissue capsule - outer cortex with nodules (B cells) - deep cortex with diffuse T cells - inner medulla with T cells - trabeculae = connective tissue going from capsule to emdulla

Question 28

pathway of lymph through lymph node

Answer 28

1. afferent lymphatics 2. subcapsular sinus (simple squamous epithelium) 3. trabecular sinus 4. medullary sinus 5. efferent lymphatics exiting at hilium

Question 29

pathway of lymphocytes from blood through the lymph node

Answer 29

entry/exit through high endothelial venules \*simple cuboidal epithelium

Question 30

spleen function

Answer 30

- platelet resevoir - destroys defective/aged RBCs (red pulp) - recycles iron - immune reactions to blood borne antigens by B and T cells (white pulp)

Question 31

spleen structure

Answer 31

- dense connective tissue **capsule** - **red pulp** - **splenic sinuses** = venous channels with long endothelial cells with gaps bewteen them, parallel to axis of sinus, perpendicular to strips of basal lamina, allow blood cells to pass through walls of sinus - **splenic cords** = meshwork of reticular cells and fibers among dense aggregations of RBCs and mΦs - **white pulp** - **periarterial lymphatic sheaths** = dense aggregates of T lymphocytes + B lymphocyte nodules surrounding central arteries - spelnic artery enters at hilium =\> trabecular arteries =\> central arteries - connective tissue **trabeculae** into interior

Question 32

open system of splenic blood flow

Answer 32

- central arteries =\> sheathed capillaries surrounded by macrophages =\> splenic cords where blood percolates through reticular meshwork and macrophages do their thing =\> splenic sinuses =\> trabecular veins =\> splenic vein \*other mammals have a closed system where arterioles =\> splenic sinuses

Question 33

thymus function

Answer 33

- T cell maturation

Question 34

thymus structure

Answer 34

- decays/turns into fat over time after immune system develops - connective tissue capsule - interconnected lobules - cortex has densly packed T cells (stains darker; basophilic) - medulla has less densly packed cells and geminal centers - trabeculae carry blood; no sinuses for lymph