cells and organs

Question 1

what are the primary lymphoid organs?

Answer 1

the Thymus and Bone Marrow - where immune cells develop

Question 2

what are the secondary lymphoid organs?

Answer 2

Spleen, lymph nodes, MALT, GALT, SALT, etc - where the immune response is initiated

Question 3

how are lymhoid organs interconnected to one another?

Answer 3

by blood vessels and the lymphatic system

Question 4

what is the definition of hematopoiesis?

Answer 4

the formation of blood or blood cells

Question 5

what are the hematopoeisis sites during fetal development?

Answer 5

red blood cell precursors are first found in the yolk sac around 3 weeks after fertilization. After 3-4 weeks of gestation, HSCs arise in distal aorta-gonad-mesonephros. They are they found in the fetal liver around 6 weeks after gestation, which becomes the primary site of hematopoeisis. eventually the blood marrow becomes the main site of hematopoeisis, about 5 months after gestation.

Question 6

what is the job of stromal cells?

Answer 6

to regulate HSCs, i.e., quiescence, trafficking, and differentiation

Question 7

what kind of cells include stromal cells?

Answer 7

macrophages, endothelial cells, perivascular cells, sympathetic nerves, and osteoblasts

Question 8

what is hematopoeisis maintained by?

Answer 8

cytokines, produced by bone marrow stromal cells and non-hematopoietic cells such as T cells and macrophages. It is also maintained by regulation of receptors and removal of cells by programmed cell death.

Question 9

what do self-renewing HSCs differentiate into?

Answer 9

all types of red-blood cells and white blood cells

Question 10

what are white blood cells also called?

Answer 10

leukocytes

Question 11

what two major types of progenitors do HSCs give rise to?

Answer 11

common myeloid progenitors and common lymphoid progenitors

Question 12

what are cytokines and what is their role in the immune response?

Answer 12

they are a broad group of small proteins responsible for cell signalling (interferons, interleukins, colony growth factors)

Question 13

what do cytokines must have to have in order to function as cell signallers?

Answer 13

a cognate receptor

Question 14

what is apoptosis?

Answer 14

programmed cell death, that can be observed through morphological changes, i.e., cell blebbing, fragmentation, alteration of cell permeability, and the release of apoptotic bodies

Question 15

what processes does apoptosis occur during?

Answer 15

1. contraction phase of the immune response
2. embryogenesis
3. to suppress vestigial embryonic structure
4. extended nutrient deprivation
5. eliminating self-reacting lymphocytes

Question 16

what is the main difference between apoptosis and necrosis?

Answer 16

necrosis causes inflammation and apoptosis does not. This is because during necrosis, disintegration of the cell occurs which releases intracellular contents. Whereas in apoptosis, cell blebbing occurs which keeps intracellar fragments in vesicles and is then ingested by phagocytes which degrade the material.

Question 17

where do T cells mature?

Answer 17

in the thymus

Question 18

what is the process of T cell maturation?

Answer 18

bone-marrow derived T cells enter the Thymus, where they travel up the cortex and undergo positive selection where they interact with nurse epithelial cells and mature. approximately 5% of T cells that enter the Thymus actually mature and differentiate. T cells then travel down the medulla where they undergo negative selection while interacting with nurse epithelial cells and DC’s, then exit the thymus. Through this process, they differentiate and gain specificity through acquiring different TCR’s

Question 19

what happens with thymic volume?

Answer 19

as we age, thymic volume decreases soon after birth and the volume of true thymic tissue (thymocytes, epithelium, macrophages, etc) is replaced by adipose tissue

Question 20

what is the spleen and why is it so important in the immune system?

Answer 20

the spleen is the major site of immune responses for “blood-borne” antigens/infection. Is it found behind the liver and over the kidney. The two main areas of the spleen are the red pulp and the white pulp. the red pulp is where hematopoeisis and delivery occurs, and the white pulp is where the lymphoid immune response occurs.

Question 21

what are the two distinct areas of the white pulp in the spleen?

Answer 21

the T-cell area and the B-cell area

Question 22

what is the role of lymphatic capillaries in the tissue?

Answer 22

they pick up interstitial fluid where it’s carried into larger lymphatic vessels into the regional lymph node

Question 23

what are the three distinct environments of draining lymph nodes?

Answer 23

cortex & paracortex, follicles, and the medulla. The cortex and paracortex harbors macrophages, other Ag presenting cells and Th cells. B cells are found in the cortex which is located within follicles. The medulla carries the antibody producing plasma cells.

Question 24

what are MALTs

Answer 24

Mucosal-associated Lymphoid Tissues. they represent about 50% of the lymphoid tissue and are often the first point of contact with an invading pathogen or other antigens. The role of MALT is to regulate mucosal immunity.

Question 25

what do common myeloid progenitors give rise to?

Answer 25

red blood cells, platelets, monocytes, granulocytes, and DCs

Question 26

what are the 4 types of granulocytes?

Answer 26

1. neutrophils - most common immune cell type found in blood, typically the first responders
2. eosinophils - play a role in defense against parasites and viruses
3. basophils - defense against parasites, play an important role during allergic reactions (release of histamine)
4. mast cells - do not arise from same precursors as other granulocytes, play a diverse role in immune responses

Question 27

monocytes are located in the … and macrophages are located in …

Answer 27

blood and tissue

Question 28

what do macrophages do?

Answer 28

ingest and degrade particulate antigens, producing high levels of hydrolytic enzymes

Question 29

what is the significance of MHC molecules (macrophages)?

Answer 29

some peptides may interact with MHC molecules forming complexes that move to the cell surface where they are presented to T helper cells

Question 30

what are DCs?

Answer 30

immune cells that are highly efficient at processing and presenting antigens. they are classified by their location
ex. langerhans found in epidermis and mucous membranes, interstitial DCs found in most organs, etc.

Question 31

what to common lymphoid progenitors give rise to?

Answer 31

lymphocytes - NK cells, T cells, B cells, DCs

Question 32

what lymphocytes are part of the adaptive immune sytsem?

Answer 32

T cells and B cells

Question 33

what are B cells?

Answer 33

lymphocytes that mature in the bone marrow and produce antibodies. following interaction with antigens, they differentiate into antibody-secreting plasma cells and memory cells. they are also APCs

Question 34

what are T cells?

Answer 34

lymphocytes that mature in the Thymus and express a T-cell receptor. there are two major types of T cells; cytotoxic T cells and T-helper cells. following interaction with antigens, they differentiate into effector and memory cells. they can also display regulatory functions (i.e., Treg)

Question 35

what are CD molecules?

Answer 35

cluster of differentiation molecules, often used to identify different cells and subtypes

Question 36

what is the difference between the innate and adaptive immune systems?

Answer 36

Innate:
include; macrophages, DCs, Mast cells, NK cells, complement proteins, granulocytes.
It is always ready for activation, and is non-specific to the antigen/infection. it produces and early and rapid response.

Adaptive:
include: B cells and T cells
this immune response exhibits more specificity, diversity, memory, and self/non-self recognition

Question 37

what do both T cells and B cells depend on?

Answer 37

clonal generation of diversity through genetic rearrangements and selections - allows for the production of millions of clones of T and B cells, each specific for different things

Question 38

what are APCs?

Answer 38

antigen presenting cells, come mostly from myeloid derived cells (DCs, circulating monocytes, macrophages, neutrophils). Also includes some lymphoid cells such as B cells.