Cells and molecules of the immune system

Question 1

what are hematopoietic stem cells

Answer 1

are the stem cells that give rise to other blood cells. The process occurs in bone marrow

Question 2

erythroid lineage

Answer 2

gives rise to erythrocytes (red blood cells) and megakaryocytes

Question 3

megakaryocytes

Answer 3

is a large bone marrow cell responsible for the production of blood thrombocytes (platelets), which are necessary for normal blood clotting

Question 4

myeloid lineage

Answer 4

this gives rise to cells of innate immunity. This includes: monocytes, macrophages, neutrophils, basophils, eosinophils, erythrocytes, and megakaryocytes to platelets.
Both the myeloid and lymphoid lineages give rise to dendritic cells

Question 5

lymphoid lineage

Answer 5

this gives rise to cells of adaptive immunity and NK cells. This includes: T lymphocytes, B lymphocytes and natural killer (NK) cells. Both myeloid and lymphoid lineages give rise to dendritic cells

Question 6

granulocyte

Answer 6

are white blood cells that have small granules or particles. These granules contain numerous proteins that are responsible for helping the immune system fight off viruses and bacteria. Neutrophils, eosinophils, and basophils are three types of granulocytes

Question 7

natural killer (NK) cells

Answer 7

are part of innate system as they do not require prior activation. They are cytotoxic; have small granules in their cytoplasm which conatin proteins such as perforin and proteases (both are granzymes). perforin forms pores in the target cell which granzymes and other molecules can enter and induce apoptosis.
They are activated by interferons or macrophage cytokines.
They are important in viral infections and cancer cells.

Question 8

mast cell

Answer 8

plays a sentinel role in the protection of epithelial surfaces. They are filled with basophil granules. They release histamines and other substances during inflammatory and allergic reactions.

Question 9

macrophage

Answer 9

are long-lived cells derived from monocytes. They have a sentinel role in tissues - provide immune surveillance. They are involved in the detection, phagocytosis and destruction of microorganisms. They are also antigen presenting cells (APCs) towards T cells. They initiate inflammation by releasing cytokines. They have Toll-like receptors that recognise bacterial products. They also recruit neutrophils from the bloodstream by sending signals.

Question 10

dendritic cell

Answer 10

As immature cells they operate as phagocytes but rather than destroying the micro-organisms they ingest, their function is the display the ingested particles on their surface for recognition by T lymphocytes. Naive dendritic cells are waiting in tissues fpr damage or infection (sentinel); they engulf pathogens and display their antigen and migrate into secondary lymphoid tissue to activate adaptive response - they are APCs. They can be activated by microbial components or inflammatory cytokines from macrophages. The are located in the mucosal epithelium of the gut, the keratinised epidermis (Langerhans cells) and the dermal layer of the epidermis (dermal dendritic cells)

Question 11

myeloid progenitor cells

Answer 11

are precursors of red blood cells, platelets, granulocytes, monocyte-macrophages, dendritic cells and mast cells and osteoclasts

Question 12

polymorphonuclear leukocytes (PMNs)

Answer 12

these are neutrophils, eosinophils and basophils

Question 13

T lymphocytes

Answer 13

kill virus infected and cancerous cells or activate other cells of the immune system. Naive T cells recognise antigen displayed by MHC on APCs which then allows them to diffrentiate into effector cells.

Question 14

CD8 cytotoxic T cells

Answer 14

are cytotoxic T cells. CD8 is a co receptor for MHC class I molecules. mainly for virus infected or cancerous cells. When it recognises antigen it becomes activated and secretes cytokines and cytotoxic granules (resulting in apoptosis).

Question 15

CD4 helper T cells

Answer 15

are helper T cells. CD4 is a co receptor for MHC class II molecules. They recognise antigen displayed by APCs which stimulates production of cytokines that help activate cytotoxic T cells and macrophages to destroy infected cells. They also activate B cells. when they bind to the antigen displayed by the B cell, they cause the B cell to proliferate and diffrentiate into an antibody secreting plasma cell.

Question 16

B lymphocytes

Answer 16

secrete antibodies. They internalise antigens bound to their suface by APCs and deliver them to endosomal compartments in the cell where they are digested into fragments. the antigen fragments can then binds to MHC class II molecules and recognised by helper T cells, which then activate the B cell to proliferate and diffrentiate into an anti-body secreting plasma cell

Question 17

neutrophil

Answer 17

They are granulocytes that undergo phagocytosis and destroy microorganims via microbicidal productes stored in vesicles (phagosome) As diffrentiated neutrophils they cirulate the bloodstream until they are recruited by macrophages. They recognise the site of infection by following IL-8 (cytokine) trail. They can also be recruited with the aid of cathelicidins and cytokines.

Question 18

eosinophil

Answer 18

a granulocyte that plays a role in the protection of epithelial cells and promotes allergic reactions. They are recruited from the bloodstream into tissues at sites of inflammation. Upon activation they release inflammatory mediators. They are Important for immune defence against parasites.

Question 19

basophil

Answer 19

a granulocyte that plays a role in the protection of epithelial surfaces. It is recruited from the blood stream. It releases histamines that mediate allergic and inflammatory responses like coughing and sneezing, which are able to expel large pathogens. When stimulated they release their granule contents including histamine. Active basophils also produce cytokines. It can aslo be activated by complement

Question 20

monocyte

Answer 20

is a phagocyte. It is the largest type of leukocute and can diffrentiate into macrophages and myeloid lineage dendritic cells.

Question 21

chemokines

Answer 21

a chemotactic cytokine. They act as chemoattractants, leading to the migration of immune cells to an infection site. They also regulate lymphoid organ development and T cell diffrentiation and tumour cell metastasis. chemokine receptors belong to the GPCRs ( G-protein coupled receptors)

Question 22

cytokines

Answer 22

signalling molecules that induce the inflammatory response by increasing the permeability of blood vessels (allowing cells to squeeze though into tissue) and recruiting additional cells and molecules to the site of infection.
Cytokines activate the adaptive immune response. Macrophages secrete theis cytokines: IL-1beta, TNF-alpha, IL-6, CXCL8 and IL-12

Question 23

M cell

Answer 23

specialised epithelial cells that deliver antigen from the lumen (gut) to underlying tissue where dendritic cells cluster activating the immune repsonse

Question 24

Langerhans cell

Answer 24

dendritic cells in the epidermis; residing in the basal and suprabasal layers of the epidermis and in the epithelia of the respiratory, digestive and urogenital tracts.

Question 25

plasma cell

Answer 25

a fully diffrentiated B lymphocyte which produces a single type of antibody.

Question 26

lymphoid tissues

Answer 26

leukocytes, bone marrow, thymus, spleen and lymph nodes

Question 27

antigen presenting cells (APCs)

Answer 27

include macrophages B cells and dendritic cells that present antigen via MHC molecules to either cytotoxic or helper T cells

Question 28

IL-1beta (secreted by macrophages)

Answer 28

activates vascular endothelium. activates lymphocytes. Local tissue destruction. increases access of effector cells

Question 29

TNF- alpha (secreted by macrophages)

Answer 29

Activates vascular endothelium and increases vascular permeability, which leads to increased entr of IgG, complement, and cells to tissues and increased fluid drainage to lymph nodes

Question 30

IL-6 (secreted by macrophages)

Answer 30

Lymphocyte activation. Increased antibody production

Question 31

CXCL8 (secreted by macrophages)

Answer 31

chemtactic factor recruits neutrophils, basophils and T cells to site of infection

Question 32

IL-12 activates (secreted by macrophages)

Answer 32

Activates NK cells. Induces the diffrentiation of CD4 T cells into TH1 cells

Question 33

Antibodies or immunoglobulins

Answer 33

they are glycoproteins synthesised by plasma cells (mature B cells). They circulate in the blood. Part of adaptive immunity. flexible Y shape structure with Fc and Fab domains

Question 34

Fab domain

Answer 34

There are 2 fab domains on an antibody - the arms of the Y shape. This is the domain that binds to antigen. Each fab domain has one heavy chain and one light chain. Each domain also has a varible heavy and varible light part of the chain which give the antibody its specificity. These hypervariable regions form loops. They hypervaribale loops are what takes part in binding

Question 35

Fc domain

Answer 35

the fragment that crystallizes. This domain binds to the cell/ cell receptor

Question 36

Complementarity determining regions (CDRs)

Answer 36

are part of the variable chains in immunoglobulins (antibodies) and T cell receptors, generated by B-cells and T-cells respectively, where these molecules bind to their specific antigen. A set of CDRs constitutes a paratope

Question 37

IgG

Answer 37

a monomer, has a longer lifetime in plasma. part of the secondary response. Has a gamma heavy chain.

Question 38

IgM

Answer 38

has 5 Y shape units, therefore, 10 places antigen can bind. Part of the primary response, usually the first antibody to be secreted by activated B cells. Has a u heavy chain

Question 39

IgA

Answer 39

Most prevalent antibody in mucosal secretions, it is transcytosed into the intestinal lumen. can exist as a monomer, dimer and trimer. Protects mucous membranes. Has a alpha heavy chain

Question 40

IgE

Answer 40

Exists as a monomer. Protects agains parasites. Has an epseilon heavy chain.

Question 41

MHC class I molecules

Answer 41

They communicate with CD8 T cells. They display anitgens derived from pathogens that replicate in the cytoplasm, the antigen displayed is recognised by cytotoxic T cells.

Question 42

MHC class II molecules

Answer 42

They communicate with CD4 T cells. Antigen derived from internalised microorganisms in endosomal compartments by lysosomal porteases, the antigen displayed is recognised by helper T cells

Question 43

Epitope

Answer 43

on antigen and is the specific region bound by the variable region of an antibody

Question 44

Paratope

Answer 44

the antigen binding region of an antibody (Fab)

Question 45

Secretory component of IgA

Answer 45

protects IgA from proteases from bacteria present in mucus and anchors IgA at the desired location.

Question 46

ITAMS

Answer 46

immunoreceptor tyrosine-based activation motif. This is a conserved motif that is part of a mechanism for signal transduction in antigen receptors, Fc receptors and some activating receptors of NK cells

Question 47

Complement

Answer 47

leads to a cascade of reactions that occurs on the surface of pathogens and generates active components with various effector functions. All complement pathways generate a C3 convertase which cleaves complement component C3 into C3b and C3a

Question 48

Classical pathway of complement

Answer 48

recognsies the antibody/antigen complex - recognises bound IgM or IgG. Also triggered by the binding of C1 to pathogen

Question 49

Lectin pathway of complement

Answer 49

recognises carbohydrates such as mannose or N-acetyl glucosamine. Also intiated by solubule carbohydrate-binding proteins - mannose binding lectins (MBL) and ficolins- these bind to carbohydrates on microbial cell walls. Proteases called MASPs (MBL assoicated serine proteases) that trigger cleavage of complement proteins and acivation of the pathway

Question 50

Alternative pathway of complement

Answer 50

Recognises cell surface proteins and polysaccharides e.g. LPS. Initiated by spontaneous hydrolysis and activation of complement component C3, which can then bind directly to microbial surfaces.

Question 51

C3b

Answer 51

complement protein that can act as an opsonin. Can also bind C3 converatses to form C5 convertase

Question 52

C5 converatase

Answer 52

cleaves C5 liberating the highly inflammatory peptide C5a and generating C5b

Question 53

C5b

Answer 53

initiates late events of complement in which proteins interact with C5b to form membrane attack complex (MAC) - this is a pore in the bacterial cell wall that causes lysis of the microbe. other proteins are needed for the stabilisation of the pore

Question 54

C5a and C3a

Answer 54

are solube and cause inflammation. They bind to receptors o mast cells that triggers degranulation and release of histamines and tumour necrosis factor alpha (TNF-alpha) which also causes inflammation

Question 55

collectins

Answer 55

are part of the innate immune system and are soluble pattern recognition receptors (PRRs). They bind to oligosaccharide struture or lipids on the surface of pathogens. Can fucntion as opsonins - cause aggregation of pathogens. They can bind to PAMPs. MBL is also part of the lectin family

Question 56

surfactant proteins

Answer 56

The epithelium of the respiratory tract is lubricated by a layer of phospholipids and proteins known as surfactants - a fluid secreted by the cells of the alveoli that serves to reduce the surface tension of pulmonary fluids. Surfactant proteins A ans D are collectins that function as opsonins

Question 57

ficolins

Answer 57

are lectins. ficolins are secreted, lectin-type pattern recognition receptors, and similarly activate the lectin pathway of complement activation. They bind to N-acetylglycosamine (GlcNAc)

Question 58

Slippied strand mispairing

Answer 58

is a mutation process which occurs during DNA replication. It involves denaturation and displacemnet of DNA strands, resulting in mispairing of the complementary base

Question 59

Phase variation

Answer 59

can generate different varients of the same strain. This happens by genes being switched on or off or rearranged. It is reversible and allows bacteria to vary their expression fo antigens

Question 60

Antigenic diversity

Answer 60

Bacteria that can change their antigenic makeup- they chnage their suface architectiure by changing key proteins or polysaccharides

Question 61

antigenic shift (virus)

Answer 61

Antigenic changes that result from reassortment of the segmented RNA genome of the human influenza virus and animal influenza virus in an animal host, in which the hemagglutinin gene from the animal virus replaces the hemagglutinin gene in the human virus. This cause major changes in expressed hemagglutinin so there is very little or no cross reaction with antibodies

Question 62

antigenic drift (virus)

Answer 62

point mutations caused in the genes encoding the two major viral suface glycoproteins - hemagglutinin and neuraminidase. The mutations alter epitopes in hemagglutinin so that neutralising antibody no longer binds. Mutations can be relatively minor meaning there is still some cross reaction with antibodies, so most of the population still has some immunity

Question 63

interferon

Answer 63

are a group of signaling proteins made and released by host cells in response to the presence of several viruses. In a typical scenario, a virus-infected cell will release interferons causing nearby cells to heighten their anti-viral defenses

Question 64

TH1 and TH2 cells

Answer 64

are subsets of T helper cells. they produce their own cytokines. TH1 cytokines produce proinflammatory response for killing intracellular parasites - ainterferon is one of the main TH1 cytokines. Th2 cytokines have an antiinflammatory resposne and include many interleukins. In excess the Th2 responses will counteract the Th1 mediated microbicidal action