Lecture 4 & 5: Innate and Adaptive Immunity

Question 1

Describe the uniques characteristics of the innate immune system

Answer 1

The innate immune system is an imediate, but nonspecific response to pathogens mounted by phagocytic cells and natural killer cells

Epithelial barriers protect as a barrier and certain cells can secrete antimicrobial peptides called defensins

The small and large intestine also have defensins, lysozymes, mucus secreting goblet cells, and paneth cellls

There is no memory of the innate immune system - if the same pathogen infects the host months in the future, the innate response and time of response will be the same

Question 2

Cells of the innate immune system

Answer 2

1. Phagocytic Cells
2. NK Cells
3. Mediator Releasers

Question 3

Phagocytic Cells

Answer 3

Cells containing azurophilic and specific granules with anti-pathogen molecule and enzymes to lower cytoplasmic pH and generate oxidizing agents that are leathal to pathogens and surrounding tissues

Includes neutrophils, monocytes, dendritic cells, and eosinophils

Question 4

Neutrophils

Answer 4

FIRST RESPONDER

60% of all circulating white blood cells

Short lived - die once they release granules to kill the invading molecule (6-24hrs)

Rapid exit from circulation to tissue sites of injury or infection

Inductive process draws the neutrophils out of circulation into the tissue where the neutrophils phagocytize the invadding microbe and DIE

NEUTROPHILS DIE

NEUTROPHILS DIE - after release of granules

Question 5

Monocytes

Answer 5

Monocytes become long lived macrophages in many tissues and organs

5% of all circulating leukocytes

Among the first cells to encounter a pathogen, comming in after the neutrophils

Digest a pathogen and display the peptide fragment on the cell surface in the context of a MHC receptor

Has an indented nucleus

Question 6

Dendritic Cells

Answer 6

Most dendritic cells are probabbly derived from monocytes

Reside within or just below the epithilial

Major gaurds against invading pathogens

After phagocytosis of pathogen the dendritic cell migrates to the regional lymph node where itpresents a peptide fragment in the context of a MHC receptor to activate a T cell - IMPORTANT INDUCERS OF T CELL IMMUNITY

Most efficent antigen presenting cell in the body (100x more efficent)

Question 7

Eosinophils

Answer 7

Granues stain red with most blood stains

Granules are antiparasitic

Prominent meddiators of allergic reactions - levels in peripherial blood can increase with an allergic response

2-4% of circulating leukocytes

Phagocytosis of an antigen-antibody complex

Question 8

NK Cells

Answer 8

Large mononuclear cells with azurophillic granules

1-2% of all circulating leukocytes

Sample the surface of virally infected cells or tumor cells for evidence of abnomality (lack of MHC receptor) and if an abnomality is dected, the NK cell kills the infected cell

NK cells secretes molecules which activates members of the adaptive immune system (INFy)

Question 9

Mediator Releasers

Answer 9

Include basophils and mast cells

Function in immediate hypersensitivity release of histamine, heparin, and peroxidase from granules - Allergic reactions

Basophils are found circulating in peripheral blood and represent .5% of white blood cells

Mast cells are only found in tissue

Have receptors for IgE on the surface

Question 10

PAMPs

Answer 10

Pathogen associated Mononuclear Paterns

Phagocytic cells must recognize PAMPs

Very chemoatractive to neutrophils

PAMPS include:

1. Terminal mannose residues
2. Double stranded RNA in viruses
3. Short sequence unmethylated CPG motif in bacteria
4. LPS - lipids in lipopolysacharide of microbes

Question 11

TLR

Answer 11

Toll Like Receptor

When a TLR is bound to a PAMP on a pathogen, it activates a signaling pathway so that phagocytic cells can release infamitory mediators to further activate the immune system

TLR activation leads to translocation of NFkB to the nucleus, where NFkB activates the transcription of genes that produce cytokines that activate the immune response

Humans have at least 10 TLRs which lead to the translocation of NFkB into the nucleus

Question 12

Activation of TLR4

Answer 12

1. LPS (a PAMP) binds to TLR4
2. Activated TLR4 releases the activated form of MyD88
3. MyD88 activates NFkB translocation to the nucleus
4. NFkB transcibes INF (interferon) inducible genes
5. Accute inflamation occurs and adaptive immunity is stimulated

TLR4 activation can also promote the transcription of proinflamatory genes through IRF5 and Jun/Fos creating an antiviral like state

There are also TLRs that can be activated within the cell located in endosomes

Question 13

Activation of IL1

Answer 13

1. After NFkB is activated and induces the transcription of the inactive form of IL1 (ProIL1) it is cleaved and eleased into circulation, which can cause accute inflamation
2. The NLRP3 inflamasome is activated through ion concentration, and does not require a TLR. The inflamasome cleaves Pro-IL1 by releasing casoase and activating IL1 to be released into circulation

Secreted IL1 cause Accute Inflamation

Question 14

Phagocytic Cells Engulf and Destroy Pathogens

Answer 14

1. A microbe identified by an antibody or complement binds to the Fc receptor or complement receptor of the macrophage
2. The microbe is endocytosed
3. Cytoplasmic NADPH oxidase on the phagosomal membrane catalyzes the production of O2 and HOCl - resulting in a respiratory burst killing the microbe
4. Neutrophils die, while macrophages process the peptide of the microbe and ppresent it in the context of a MHC class 2 molecule

Question 15

Respiratory Burst

Answer 15

After the engulfment of a foreing particle NADPH oxidase is released from the phagosomal membrane and the production the following compounds is catalize resulting in the destruction of the forgien particle:

O2

HOCl

Hydroxyl Radicals

NO

*Mammals defficent in NADPH oxidase are very suceptible to bacterial infection

Question 16

NETs

Answer 16

Neutraphil Extracellular Traps

After a respiratory burst and the death of the invading pathogen, the nuclear membrane of the neutrophil is dirupted forming punctate granules

The death of a neutrophil forms an extracellular trap that contains DNA and products of the azurophillic granules which continue to help destroy pathogens

Question 17

Production of the inflammatory response due to activated macrophages

Answer 17

Activated macrophages produce chemokines and cytokines that contribute to the production of the inflamitory response

Chemokines are chemoattractants for neutrophils monocytes, and dendritic cells

Cytokines such as IL1 cause fever and TNFa can cause septic shock

Important for the inflamitory response - recruit an army of phagocytic cells

Question 18

Production of the inflammatory response due to activated NK Cells

Answer 18

NK cells are activated by INFa and INFb

Kill virally infected cels and some tumor cells via apoptosis

Also secrete cytollines (INFy) which helps induce adaptive Immunity

Macrophages with phagoocytosed microbes secrete IL12 stimulating NK cells to release INFy which results in the macrophage killing the microbe

NK cells monitor the level of MHC class 1 molecules on host cells - when the levels of MHC class 1 molecules are low, the inhibitory receptor of NK cells is not engaged and the NK cell is activated resulting in the death of the cell

Question 19

Unique Characterisics of the Adaptive Immune System

Answer 19

CAlled in by the innate immune system when it cannot handle the pathogen

Specific antigen recognition by specific receptors on T and B lymphocytes and clonal expansion (3-5 days)

Tolerance to self antigens

Memory of response such that subsequent exposure to the same antigen results in a much more rapid response

Highly specific due to recombination of genes on TCR and BCR

Question 20

T Lymphocytes

Answer 20

Origin: Develop in the thymus and precursors come from the bone marrow

Location: Bone Marrow, Thymus, Spleen, Lymph Nodes, Tonsils, Pyers Patches, connective tissue and blood and lymph vessles

Function: When stimulated by antigen T cells develop into effector T cells (Th1, Th2, Th17, T reg) and can also develop into cytotoxic T lymohocytes

*Must see an antigen in the context of a MHC molecule on the surface of an APC

* Depends on the microbe which T cell develops

Question 21

B Lymphocytes

Answer 21

Origin: Develop in the bone marrow with surface Ig receptors to an antigen they have never seen before

Location: Bone Marrow, Thymus, Spleen, Lymph Nodes, Tonsils, Pyers Patches, connective tissue and blood and lymph vessles

Function: Upon antigen stimulation they develop into antibody secreting plasma cells with cytokine help from T cells

Question 22

Th1

Answer 22

Make INFy, IL2, TNFa

Important in delayed type hypersensitivity and other cell mediated immune responses

Macrophage activation and IgG production (to increas the uptake of bacteria)

Targets Intracellular pathogens

Activated by IL12 from dendritic cells

Question 23

Th2

Answer 23

Make IL4, IL5, IL10, and IL13

Important in humoral immunity- B cell activation

IL4 - activates B cells that produce neutralizing antibodies (IgE causes the release of granules from mast cells)

IL5 - activates eosinophils involved in parasitic infections and allergic response

Question 24

Th17

Answer 24

Makes IL17 which induces tissue fibroblasts and epithelial cells to make IL6, chemotactic cytokines, and growth factors (GCSF, GMCSF) for the stimulation of neutrophils

Target is extracellular bacteria

Implicated in various autoimmune disease

*Th17 cells also release IL22 which stimulates epithelial cells to grow and increase barier function

Question 25

T Reg

Answer 25

Downregulate Immune responses via cytokines and cell surave contact

Question 26

Cytotoxic T Cells

Answer 26

Make TNFa and cytotoxic effector molecules Perforin and granzymes Perforin makes a tube that allows granzymes to enter the cell and activate the caspase cascade, killing the cell

Question 27

Clonal Selection

Answer 27

B cells and T cells develop Ig or receptors for an antigen even before being exposed to it Antigen stimulation of a complimentary, antigen specific receptorresults in the prolliferation and differentiation of the stimulated cell 10^5 increase in 1 week of that specific cell after being exposed to the antigen **Monoclonal** - a single B and T cell clone activation **_Polyclonal -_** antigenic molecules that have many sites or antigenic determinants (epitopes) that can stimulate B cells and T cells

Question 28

Immunological Memory

Answer 28

Secondary exposure to an antigen is specific and has a shorter lag time, and the response is more robust A primary responce produces IgM, while a secondary response produces IgG (or A/E depending on the circumstances)

Question 29

Phases of the immune response

Answer 29

1. Antigen recognition 2. Clonal Expansion 3. Differentiation of plasma cells and effector T cells 4. Elimination of antigen 5. Memory

Question 30

How do cells lean not to respond to self-antigens?

Answer 30

Autoreactive B cells and T cells are normally deleted in the bone marroww or thymus hHgh affinity to a self antigen results in the deletion of the cell Weak affinity to self antigens allow the cell to mature Only a couple of % of cells make it to the periphery where they can react with an antigen

Question 31

Lymphocyte Circulation and Recirculation

Answer 31

Lymphocytes leave the blood by adhering to and squeezing between the endothelial cells of the High endothelial venule in the para cortex of the lymph node The lymphocytes stay in the lymph node for abount 12 hours unless they encounter antigen When lymphocytes leave the lymph node they exit through the efferent lymphatic whic empties into the thoraci duct and then into circulation Pathway 1. Antigen enters through the afferent lymphatic (generally picked up by dendrtitic cells) 2. Lymphocytes enter the lymh node in the HEV located in the deep cortex 3. B cells are found in the follicles, superficial cortex 4. T cells are found in the para cortex 5. If not activated the cells migrate through the medulla and leave through the efferent lymphatic

Question 32

S1P

Answer 32

If there is no antigen for an immune response T and B cells leave the node in response to a high S1P gradient in the lymph If there is an immune response they downregulate the S1P receptor and stay in the node until they beome effector cells Receptor for S1P is located on the surface of lymphocytes A recenly activated T cell will have low levels of S1P expressed and will stay in the lymph node An effector T cell days after innoculation or unactivated t cell will have high S1P receptors and leave the node \*TO KEEP A MOLECULE IN THE NODE, use a molecule that blocks the S1P receptor and downregulates the S1P receptor

Question 33

Important Chemokines for T lymphocyte location

Answer 33

CCL19 is made by the stromal cells of the paracortex and keeps T cells in the paracortex The paracortex is where mature antigen laden dendritic cells are found to activate the appropriate T cell \*once activated T cells loose receptors for CCL19 and develop receptors for CXCL13 (of B Cells) and move into the follicle to help B cells

Question 34

Important Chemokines for B lymphocyte location

Answer 34

B cell lymphocyte chemoatracant CXCL13 is made in lymphoid follicles and draws B cells there Located in the supperficial cortex

Question 35

Consequences of loosing chemokine receptors on the immune system

Question 36

HEV

Answer 36

High Endothelial Venule Venule that allows for the import of lymphocytes from the blood into the paracortex of the lymph node

Question 37

Migration of lymphocytes from the blood through the HEV into the lymph node

Answer 37

1. L selectin on the surface of the lymphocyte must bind to the GlyCam1 receptor on the endothelial cells of the HEV 2. The chemokine receptor on the lymphocyte must bind to the chemokin CCL21 - on the enothelial cells of the HEV 3. Activation of LFA1 receptor on lymphocytes by binding to ICAM1 on endothelial cells of the HEV allows the lymphocyte to move throgh the epithelial cells and migrate into the node

Question 38

What is the difference between the surface of naive cells and activated effector cells

Answer 38

Naive Cells * L Selectin * Chemoline Receptor for either CCL19 (T cell) or CXCL21 (B Cell) * LAF1/ ICAM * Allows for the migration of the naive cell to come into the node Effector Cell * E or P selectin ligan to bind to the inflamed lining of the blood vessles * LFA1/ ICAM1 * CXCR3 or CCR3