Thrush- MHC

Question 1

what type of MHCs exist in humans?

Answer 1

HLA (human leukocyte antigens) on chromosome #6 in humans

Question 2

what class to HLA-A, HLA-B and HLA-C belong too? and where are they expressed?

Answer 2

class I MHC (expressed on most nucleated cells)

Question 3

what protein do the class I genes associate with to become a class I MHC?

Answer 3

invariant (doesnt change) beta2-microglobulin

Question 4

what are the 3 classical genes that make up MHC II? and what are they produced by?

Answer 4

HLA-DP, HLA-DQ, and HLA-DR - 2 chains: alpha and beta

Question 5

is the cleft of class I open and the cleft of class II blocked?

Answer 5

no. 
class I-> blocked "anchor residues" #2 and 9
class II-> open

Question 6

in class I protein which domain(s) form the peptide binding cleft? and which domain(s) interact with CD8?

Answer 6

peptide binding->alpha1 and alpha2

CD8-> alpha 3

Question 7

in class II what area contacts the CD4 cell? and what acts as the Ag binding cleft?

Answer 7

CD4-> alpha2/beta2

Ag binding-> alpha1/beta1

Question 8

are MHC able to bind a variety of antigenic peptides?

Answer 8

yes (they are promiscuous)

Question 9

what enzymes work with proteasome to break down proteins at hydrophobic residues?

Answer 9

LMP2 and LMP7 - important for class I anchors

Question 10

what delivers class I peptide from cytosol to ER?

Answer 10

TAP-peptide

Question 11

is it true that inside a healthy cell, endogenous proteins are broken down and taken up by MHC class II and taken to the surface of the cell?

Answer 11

no. MHC class I express them on the surface. (if the cell is healthy than a T cell will not be activated unless it is an autoimmune disease)

Question 12

what do cytokines, viruses and cancer cells all have in common?

Answer 12

they can decrease MHC expression. (cytokines can also increase MHC expression)

Question 13

what is activated when a T helper cell becomes a Th1?

Answer 13

T cell cytokines help activate cell mediated response by activating inflammation and cytotoxicity (intracellular pathogens)

Question 14

what is activated when a T helper cell becomes a Th2?

Answer 14

cytokines produced will help B cell activation - humoral repsonse for extracellular pathogens

Question 15

why can we produce 6 different class I and 12 different class II proteins?

Answer 15

expression of MHC genes is co-dominant (2 for each 3 classical class I genes and 4 for each class II from alpha and beta)

Question 16

why is tissue transplantation so difficult?

Answer 16

MHC genes are polymorphic - variations in gene sequence and recombination

Question 17

what type of peptides do class II present?

Answer 17

exogenous peptides (brought into cell by endocytosis)

Question 18

MHC class II are on professional presenting cells, what are these cells?

Answer 18

dendritic cells, macrophages, and B cells (T cells can be induced to express class II but it is rare)

Question 19

what is bare lymphocyte syndrome?

Answer 19

defects in expression of class II transactivator (CIITA) - cant express class II MHC proteins and T cells cannot be activated

Question 20

what can IFN-gamma do to class II activity?

Answer 20

increase class II expression on macrophages and decrease class II expression on B cells

Question 21

what is the binding groove of class II protein filled with to prevent other peptides from associating with it?

Answer 21

protein called invariant chain (not B2-micoglobulin)

Question 22

what is left in binding groove after invariant chain is cleaved as the class II protein travels in cell from ER to surface?

Answer 22

CLIP

Question 23

when is CLIP removed from binding groove?

Answer 23

once protein + CLIP makes it to the phagolysosome - now antigenic peptide can associate with MHC class II

Question 24

what removes CLIP from binding groove?

Answer 24

HLA-DM

Question 25

what are most T cell TCRs made of?

Answer 25

alpha/beta chains or gamma/delta chains

Question 26

what do gamma/delta T cells recognize for antigen presentation?

Answer 26

CD1 instead of MHC molecules (on chromosome 1)

Question 27

what cells express CD1?

Answer 27

professional and non-professional APCs, B cells, thymocytes and epithelial cells

Question 28

what do the CD1 molecules present?

Answer 28

non-protein antigens (lipids, glycolipids) - ex. M. tuberculosis and M.leprae