Session 5 - Adaptive Immunity

Question 1

true or false: antigens activate T cells

Answer 1

false - antigen presenting cells do

Question 2

what are intracellular and extracellular microbes

Answer 2

intracellular = microbes that divide inside cells. they are usually viruses 
extracellular = microbes which divide outside of cells. these are mainly bacteria

Question 3

where are antigen presenting cells located

Answer 3

in the skin (SALT), mucus membranes (GALT, BALT), lymph organs and in the blood

Question 4

how do antigen presenting cells capture the pathogen

Answer 4

by phagocytosis (may require opsonisation) of whole microbes or macropinocytosis of soluble particles

Question 5

how do antigen presenting cells detect the pathogens

Answer 5

with their PRRs which are specific to the PAMPs on the microbes

Question 6

name 4 different APC

Answer 6

dendritic cells - found in lymph nodes, mucus membranes and blood and present to naive T cells
langerhans cells -found in the skin and present to naive T cells
Macrophages - found in various tissues and present to effector T cells
B cells - found in lymphoid tissue and present to effector and naive T cells

Question 7

what are naive T cells

Answer 7

T cells which havent yet been activated by APC

Question 8

what type of immunity is initiated by extracellular microbes

Answer 8

humoral immunity (involving antibodies, complement and phagocytosis)

Question 9

what type of immunity is initiated by intracellular microbes

Answer 9

cell dependant immunity (involving cytotoxic t lymphocytes, antibodies and macrophages)

Question 10

what is required for antigen presentation

Answer 10

major histocompatibility complex

Question 11

what is MHC

Answer 11

cell surface proteins which recognise and bind to antigens and display them on their surface for recognition by T cells

Question 12

where are class I and class II MHC molecules found

Answer 12

• found on all nucleated cells (class I)

- found on dendritic, macrophages and B cells (class II)

Question 13

what genes code for class I MHC molecules

Answer 13

HLA A, HLA B and HLA C

Question 14

What genes code for class II MHC molecules

Answer 14

HLA DR, HLA DQ, HLA DP

Question 15

true of false - classes I and II MHC molecules are co-dominant

Answer 15

true - this increases the number of different MHC molecules

Question 16

what does it mean by saying that the MHC molecules have polymorphic genes

Answer 16

there are different alleles among individuals which increases presentation of different antigens

Question 17

what peptides do MHC class I present

Answer 17

self and non-self peptides from intracellular microbes

Question 18

what peptides do class MHC class II present

Answer 18

non self peptides from extracellular proteins

Question 19

describe the structure of MHC class I molecules

Answer 19

1 heavy/alpha chain and 1 beta chain

groove which allows a peptide to bind to

Question 20

describe the structure of MHC class II molecules

Answer 20

2 chains containing alpha and beta
chains are the same length
groove for the peptide to bind to

Question 21

why is the peptide binding cleft variable

Answer 21

so that lots of different proteins can bind

Question 22

what T cells recognise MHC class I molecules

Answer 22

CD8+ (cytotoxic t - kill infected cells)

Question 23

what T cells recognise MHC class II molecules

Answer 23

CD 4+ (T helper - activates B cells and macrophages)

Question 24

which molecules go through the endogenous pathway and describe this pathway

Answer 24

intracellular - proteasomes degrade the virus into fragments. Peptides are taken to ER where they bind to MHC1 proteins before being transported to cell surface membrane. Once here they can be recognised by T cells

Question 25

which molecules go through the exogenous pathway and describe this pathway

Answer 25

extracellular - the antigen is taken up into a vesicle which fuses with a lysosome to form an endosome when the proteins are broken down. The peptide fragments bind to the MHC II molecules and move to the cell surface membrane

Question 26

true or false - peptides from the same microbes are presented by the same MHC molecule

Answer 26

false

Question 27

what are elite controllers

Answer 27

patients who can control viral replication - they have the slow progressor type of the HLA B gene and so give an effective T cell response. Others have rapid progressor HLAB gene which gives poor recognition by T cells

Question 28

what are the clinical problems of MHC molecules

Answer 28

• major cause of organ transplant due to mismatch of molecules in a allograft
• cause graft versus host reaction
• associated with autoimmune disease

Question 29

what autoimmune diseases are MHCs associated with

Answer 29

• ankylosing spondylitis (HLA B)

- insulin dependant diabetes mellitus (HLA DQ)

Question 30

through which receptors do the MHC molecules activate T cells

Answer 30

T cell receptors

Question 31

what different CD4+ T cells are acitavted and what effects do they have

Answer 31

• TH2 CD4+ = activates eosinophils, B cells and Mast cells

- TH17 CD4+ = activates neutrophils

Question 32

what is the main antibody produced in the primary and secondary response

Answer 32

primary = IgM
secondary = IgG

Question 33

describe the changes in the antibodies IgG and IgM during an immune reaction

Answer 33

during the first response there are high levels of IgM and low levels of IgG
this is reversed in the secondary response

Question 34

what is the function of IgG

Answer 34

• enhances phagocytosis
• activates complement cascade
• gives neonatal immunity
• neutralises toxins and viruses

Question 35

what are the functions of IgE

Answer 35

• allows for mast cell degranulation in allergic responses

Question 36

what is the function of IgM

Answer 36

complement activation

Question 37

what is the function of igA

Answer 37

mucosal immunity