lecture 3 exam 2

Question 1

innate immunity

Answer 1

physical & chemical barriers
phagocytes
complement system
NK cells
works for IMMEDIATE but GENERAL recognition of conserved pathogen signals

Question 2

adaptive immunity

Answer 2

works against pathogens that have eluded innate immunity
machrophages and DC BRIDGE innate & adaptive by secreting cytokines and presenting antigens to T cells
LONGER onset but more SPECIFIC recognition
two types: jumoral (antibody mediated) & cellular (Tcell mediated)

Question 3

MHC is essential to trigger adaptive immunity

Answer 3

antigens must be processed into peptides to trigger adaptive immunity
-broken up inside cells and bound to antigen-presenting receptors
antigen presenting receptors are encoded by genes clustered together to form the MHC

all vertebrates have different variation of MHC

Question 4

MHC 1

Answer 4

receptors for endogenous antigen found on most nucleated cells (except RBC)
dont eat me signal on non APC
TCR of CD8+

a1, a2, a3, b2m
a - 43kDa
b2microglobulin is 12kDa - nonMHC encoded, non transmembrane, noncovalently bound to a chain

present intracellular origin derived antigens

Question 5

MHC 2

Answer 5

receptors for exogenous antigen predominantly found on APC (B cells)
professional antigen presenting cells, T cells
TCR of CD4+

2a 2b
a - 34 kDa
b - 29 kDa
no b2microglobulin

can accomodate peptides w more than 13 aa
present extracellular derived origin antigens

Question 6

MHC 3

Answer 6

mixed group of proteins including some complement components, TNF

Question 7

polygenism

Answer 7

multiple genes encoding different types of MHC molecules w a range of peptide binding specificities

Question 8

polymorphism

Answer 8

variations at a single genetic locus in a population level

different versions of each gene among individuals in a pop
pop survival depends on expression of a sufficient number of diff MHC genes to enable at least some individuals to overcome infection by a new pathogen

affects peptide antigen binding
changes in pockets, walls and floor of peptide binding cleft

Question 9

codominance

Answer 9

gene copies expressed from both parents
inheritance of MHC is codominant
heterozygous state increases the diversity of antigens that can be recognized

Question 10

haplotype

Answer 10

complete set of alleles found within an individual animal’s MHC

Question 11

properties that result in heterogeneity of MHC molecules across population

Answer 11

polygenism
polymorphism
codominance
haplotype

Question 12

T cells must encoutner their antigen presented in context of MHC

Answer 12

APC processes antigen that T cells recognize
APC generate fragments of antigens that associate w MHC 1 or 2 that are displayed on the plasma membrane
cells that activate an immune response by presenting antigen to T cells are called professional APC

Question 13

professional APC

Answer 13

DC
macrophages
B cells

activate immune response by presenting antigen to T cells

Question 14

characteristics of MHC molecules

Answer 14

1. MHC can present one peptide at a time
2. an MHC molecule is capable of presenting different peptides at different times
3. anchor residues are critical amino acids and must fit into binding pockets (limited variability)
4. broad specificity = an MHC molecule can bind an array of different peptides (est. <10,000 diff peptides/MHC molecule

can bind peptides of differnet length

Question 15

motif

Answer 15

common sequence in a peptide antigen that binds to an MHC molecule

Question 16

anchor residues

Answer 16

amino acids common to many peptides tether the peptide to structural features of the MHC molecule

need not be idental but must be related - Y & F = aromatic, V, L & I are hydrophobic

Question 17

MHC presentation of antigen induces innate immunity by activating T cells

Answer 17

TCR accessory molecules (CD8 & CD4) determine w which MHC class T cell will interact = class restriction

MHC 1 - 8
MHC 2 - 4

occurs in light zone of lymph nodes

Question 18

MHC are targets for immune evasion by pathogens

Answer 18

T cells are required for an effective adaptive immune response
ag-specific t cells must be activated by peptide MHC complexes
there is a strong selective pressure for pathogens to mutate genes encoding antigens so that they can evade formation of peptide/MHC complexes

in order to prevent this pathogen evasion we have more than one type of MHC molecule in each individual and there are extensive differneces between individuals