3: Adaptive Immunity

Question 1

what does the adaptive immune system do?

Answer 1

responds to pathogens by specifically recognising antigens

Question 2

innate vs. adaptive immune system

Answer 2

both provide self/non-self differentiation

adaptive recognises the type of bacteria and specific antigens
- more exquisite recognition since it recognises antigens
- high specificity and memory

innate only knows that it is present

Question 3

antigens

Answer 3

molecules from pathogens recognised through the immune system

non-pathogens can also be antigens

Question 4

pitfalls of innate and adaptive immune systems

Answer 4

both can have incorrect responses to pathogens and you end up with auto-immunity or other diseases

Question 5

what does the adaptive immune system recognise?

Answer 5

smaller pieces of antigens called epitopes or antigenic determinants

Question 6

relationship between pathogens, antigens and epitopes

Answer 6

pathogens made up of different antigens

each antigen can have many epitopes

Question 7

characteristics of adaptive immunity

Answer 7

distinguish between small differences in antigens
- greater specificity than innate

takes 5-7 days to initiate antigen specific adaptive immune responses when exposed to pathogens
- takes longer than innate

creates immune memory cells that provides a faster immune response when infected again with the same pathogen
- memory unlike innate

Question 8

immunological memory

Answer 8

second exposure to an antigen results in a more potent immune response

differentiate between vaccine antigens and antigens in the virus
- some viruses have envelope proteins that you’ve never seen before infection so vaccines don’t help

Question 9

what should the adaptive immune system do when correct?

Answer 9

should only respond to foreign and harmful, not to foreign and not harmful

Question 10

adaptive immunity responses initiation

Answer 10

primary infection/first exposure
- takes a few days to initiate
- T and B cells have to be activated and expanded, then spread around the body

secondary infection/subsequent exposure
- quicker adaptive immune response because of memory cells that can be activated quicker when they recognise the pathogen

Question 11

cells of the adaptive immune system

Answer 11

all lymphocytes

T cells or B cells
- cytokines come and bind to the surface of cells to activate them
- DCs as important in this process

macs and DCs play important roles in activating adaptive immunity but do not form memory cells

Question 12

B cell mediated immunity

Answer 12

antibodies produced by B cells interact with pathogens and their toxic products in the blood or other spaces
- B cells recognise antigens whereas T cells recognise proteins

B cells activated from the virus just being there

Question 13

T cell mediated immunity

Answer 13

T cells only recognise antigens as small peptide fragments bound to MHC molecules and displayed at the cell surface

controlling the immune system and killing infected cells

Question 14

3 tools of the adaptive immune response

Answer 14

antibodies made by B cells

cytokines made by T helper cells

killing of infected cells by cytotoxic T cells (CTLs)
- only cells that are memory cells and lymphocytes
- harness all other immune cells (neutrophils and macs)

Question 15

main function of B cells

Answer 15

antibody mediated immune response

main function to produce antibodies

Question 16

antigen binding sites / variable regions (Fab)

Answer 16

one part binds specifically to antigens

highly variable

each antibody has 2 identical Fabs which are specific to an antigen

Question 17

constant region (Fc)

Answer 17

binds to other immune cells

4 main antibody isotypes
- IgM, IgG, IgA and IgE
- IgA important because it’s the mucosal antibody

memory antibody during immunisations leads to mostly IgG
- if you get infected and make many antibodies, it will be both IgG and IgA

Question 18

functions of antibodies

Answer 18

neutralisation
- antibodies bind to antigens to block toxin function and neutralise them
- mostly IgG and IgA

opsonisation
- antibodies enhance phagocytosis
- bind to surface of the pathogen to enhance phagocytosis
- mostly IgG and IgM

phagocytosis and lysis
- mostly IgG and IgM
- binds to pathogens or infected cells to kill them

Question 19

neutralisation

Answer 19

blocks active site for adherence

neutralising antibodies usually high affinity so better at binding

mainly IgG and IgA
- spike neutralising IgG from vaccines but IgA also helps neutralise when you get infected

Question 20

opsonisation

Answer 20

Fc of antibody binds to Fc receptors on phagocytic cells to provide enhanced uptake

complement activation
- complement protein binds to Fc receptors
- whole bunch of enzymes to lyse pathogens

Question 21

2 main types of T cells

Answer 21

cytotoxic T cells (CD8 T cells)
- specifically kills virally-infected cells

T helper cells (CD4 T cells)
- produce cytokines

Question 22

T helper cells (Th)

Answer 22

master regulators of adaptive immune responses

key immune cells need cytokines produced by Th to be activated
- Th cytokines mostly different than innate immunity cytokines

cytokines needed for
- B cells to produce antibodies
- cytotoxic T cells to become maximally effective killers
- macs to kill pathogens inside

Question 23

T cell receptors (TCR)

Answer 23

specific to one antigen and one epitope for each pathogen

activates T cells

each T cell has only one unique TCR but will have many copies of that same TCR

similar to antibodies with a variable and constant region

only recognises antigen when the antigen is presented by specialised molecules (MHC)

Question 24

major histocompatibility (MHC)

Answer 24

MHC molecules display fragments of pathogens on the host cell surface on the DC to present to T cells

antigen taken up by phagocytosis by DC, DC presents antigen with MHC molecules, looks for T cell with TCR specific to that

MHC called HLA (human leukocyte antigen) in humans

Question 25

how do DCs initiate adaptive immune response?

Answer 25

DCs pick up pathogens at sites of infection, then bring it to lymph nodes or spleen

a DC can bind to 50-100 T cells to present antigens and activate them

Question 26

how are cytotoxic T cells activated?

Answer 26

when activated, known as CTLs (cytotoxic T lymphocytes)

when TCR of a specific CTL recognises antigen presented on MHC by infected cell, CTL kills infected cell

CTL killing is very specific
- targets infected cells unlike other immune cells