Addaptive Immunology

Question 1

Adaptive immune system function

Answer 1

Creates immune response to specific antigen

Question 2

What is an antigen

Answer 2

Foreign protein or other molecule that is the target of an immune response

Question 3

Adaptive immunity cells

Answer 3

• antigen presenting cells (APCs) present antigen complexed with MHC (major histocompatability) class II proteins on cell surface
  Occurs in lymph nodes, leads to cytokine signaling and lymphocytes activation
• T lymphocytes
  Helper T cells (CD4+) or cytotoxic T cells (CD8+)
• B lymphocytes
  Memory B cells, plasma B cells

Question 4

B lymphocytes function

Answer 4

Memory B cells- secondary immune response to same antigen
Plasma B cells- make antibodies, bind to specific antigen

Question 5

Two types of adaptive immunity

Answer 5

Humoral immunity- fights invaders outside cells (bloodstream)
- bacteria and toxins
- involves plasma B and antibodies
Cellular immunity- attacks antigens found inside cells
- virus, fungi, parasites
Involves cytotoxic T cells and natural killer cells

Question 6

What happens when B cells activate

Answer 6

Undergo clonal expansion (proliferation) producing plasma cells and memory cells (long lived)

Question 7

What can activate B cells

Answer 7

T independent antigens activate B cells directly
T dependent antigens require activation of helper T cells that produce cytokines to activate B cell indirectly
T-independent = direct activation
T- dependent - indirect activation

Question 8

What determines t-dependent or independent

Answer 8

Type of antigen
Amount present

Question 9

Where do antigen-antibody complexes go

Answer 9

Cleared by complement cascade or
Liver or spleen

Question 10

What is co stimulation of B cell

Answer 10

1. Antigen bind to B cell receptor
2. T cell receptor interacts with antigen presenting MHC class II protein
   - two signals for B cell to become activate and mature into plasma cell

Question 11

Why is co stimulation of B cell important

Answer 11

Two signals to all B cell activation and mature
Ensure that the B cell activation is required, not an oops with correct antigen binding or an oops with TCR binding to MHC II
Prevent immune overdrive

Question 12

Plasma B cell creation stages

Answer 12

1. Stem cells differentiate into mature B cells, each bearing surface immunoglobulin against specific antigen- checks that receptor shape doesn’t target body cells, and that it targets antibody effectively- after success CLONE EXPANSION of specific antibody
2. B cell encounters specific antigen and proliferates (into plasma and memory)
   3a. B cells proliferate into long lived memory cells (these memory cells can be used at a later date, stimulated by antigen, become plasma cell)
   3b. Plasma cells secrete antibodies into circulation

Question 13

Acquired immunity: antigen-specific responses

Answer 13

All responses result in antibody binding to antigen
1. Agglutination: clumping of bacteria so all in localized region, easy antibody pick up
2. Opsonization: coat antigen with multiple antibodies enhances phagocytosis, easier for macrophage to engulf
3. Neutralization: blocks adhesion of bacteria/virus to mucosa and blocks attachment of toxin. Antibodies bind to virus, bacteria, toxin
4. Antibody-dependent cell-mediated cytotoxicity: used for parasites (large bad cells) can’t engulf. Antibodies coat the parasite allowing macrophages, eosinophils, natural killer cells to destroy using lytic enzymes, perforin
5. Activation of complement: protein binds to antibody on bacteria, put holes in bacteria cell wall, cause inflammation and cell lysis

Question 14

Where are T cells produced and matured

Answer 14

Produced in red bone marrow
Mature and undergo ‘thymic selection” in the thymus

Question 15

Function of T cell receptor

Answer 15

Antigen binds- every T cell has one specific antigen

Question 16

How are T cells activated

Answer 16

Antigen presenting cell (APC) that has antigen complex with MHC II- could be B cell in t-dependent, dendritic cell, infected body cell

Question 17

How are different T cells made and what MHC do they interact with

Answer 17

CD4+ and CD8+ are receptors

CD4+ T cells become helper T cells. Interact with MHC II present on APCs or MHC I on infected cells
CD8+ T cells become cytotoxic T cells. Interact with MHC I found on all nucleated cells of body (not RBC)

Question 18

What other things can helper T cells become

Answer 18

Memory T cells

Question 19

TH cell activation

Answer 19

1. An APC encounters and ingests a micro-organism. Antigen is enzymatically processed into short peptides which combine with MHC class II molecules and are displayed on surface of APC
2. TCR on surface of CD4+ helper cell binds to MHC antigen complex. TH cell or APC is stimulated to secrete co-stimulatory molecule. (Co-stimulatory molecule required to activate T cells that have not previously encountered antigen). Two signals activate TH cell produce cytokines
3. Cytokines cause TH cell to activate

Question 20

TC activation

Answer 20

1. Virus-infected cell or cancer cell (MHC class I body cells) produce abnormal endogenous antigens
2. Abnormal antigen is presented on cell surface in association with MHC class I molecules. Binding of TH1 cell to MHC class I antigen presenting promotes secretion of cytokines
3. Cytokines activate a precursor CTL which produces a clone of CTLs (cytotoxic T cell activation)
4. CTL induces destruction of the virus-infected cell by apoptosis

Question 21

T cell precursor differentiation

Answer 21

1. ? Somehow -> natural killer cells -> kill antibody coated cells or bacteria, MHC class I APC
2. Migrate to thymus -> cytotoxic T cells -> kill MHC class I APC
3. Migrate to thymus -> helper T cell -> bind to MHC class II APC or MHC class I antigen infected cell -> secrete cytokines that activate other immune cells

Question 22

Pathway of complement activation

Answer 22

Antibody binds to antigen and activates C1
C1 splits and activates C2 and C4
C2a+ C4b come together -> C3
C3 split into C3a + C3b (diff jobs)
C3a- function inflammation
C3b- function in cytolysis and opsonization (coating pathogen)

Question 23

Outcomes of complement activation

Answer 23

Cytolysis (apoptosis)
C3b activate C5
C5 split C5a + C5b
C5b activates C6
C6, C7, C8, C9 get together, form ring, enter pore -> apoptosis
Opsonization
C3b act like antibodies and coat. Makes life easier for macrophage/ phagocyte to locate and engulf
Inflammation
C3a binds to receptor of mast cells -> Histamine release
And
C3b -> c5 -> C5a + C5b -> C5a bind to receptors of mast cells -> histamine release

Question 24

What happens without immunity

Answer 24

Graph # of micro-organisms vs duration of infection (t)
- lacking innate - no physical/chemical barriers, huge increase in micro-organisms
- lacking adaptive - still have barriers working, but overtime invaders increase and no antibodies or T cells to remove them
- normal human graph a parabola- down as recovery

Question 25

Interferons creation and use pathway

Answer 25

1. Viral RNA from an infected virus enters the cell
2. Virus induces the host cell to produce interferon mRNA (IFN-mRNA) which is translated into alpha and beta interferons
3. Interferons make contact with uninflected neighbouring host cells -> bind to plasma membrane or nuclear receptors. Interferons induce the cells to synthesize antiviral proteins (AVPs)
4. AVPs degrade viral mRNA and inhibit protein synthesis (outcome- interfere with viral replication)

• interferons made in infected cell
• interferons make uninfected cell synthesize antiviral proteins
• by the time cell becomes infected, AVP will degrade viral mRNA