B3.060 Dysregulation of Immune Signaling in Human Disease

Question 1

triad of clinical manifestations for classic Wiskott-Aldrich Syndrome (WAS)

Answer 1

recurrent bacterial and viral infections
extensive eczema
thrombocytopenia/ microplatelets (1/2 volume)

Question 2

what are WAS patients at risk for later in life

Answer 2

autoimmunity and malignancy

Question 3

what is the function of WASp

Answer 3

links cell signaling to the actin based cytoskeleton

actin polymerization

Question 4

what are the segments of WASp

Answer 4

EVH1
BR
GBD
PPPPP
VCA

Question 5

EVH1 region

Answer 5

binds WIP to keep protein inactive

Question 6

BR region

Answer 6

basic region, binds to PIP2 and moves protein to immune synapse

Question 7

GBD region

Answer 7

GTPase binding domain (cdc42)

Question 8

PPPPP region

Answer 8

proline rich SH3 domain where adaptors bind, required for immune synapse formation

Question 9

VCA region

Answer 9

verprolin-like, central and acidic regions bind Arp2/3 complex when active, leading to nucleation of actin filaments

Question 10

what conformational change takes place in the WASp

Answer 10

when GTP-bound cdc42 binds, protein springs open into active conformation
phosphorylation stabilizes

Question 11

features of classic WAS

Answer 11

50%
absent or truncated WASp
premature terminations/ deletions

Question 12

features of X-linked thrombocytopenia

Answer 12

mild disease, 50%
mutated, non functional protein, missense mutations
lower quantities, normal size
no autoimmunity

Question 13

features of X-linked neutropenia

Answer 13

very very rare
missense mutation in GTPase binding domain
no autoinhibitory action of protein
uncontrolled actin polymerization

Question 14

what would be expected T and B cell counts in a 9 month old with WAS?

Answer 14

normal levels
WASp not involved in initial development of T and B cells
just involved in formation of immune synapse

Question 15

describe the difference between normal WBCs and WAS patient WBCs on electron microscopy

Answer 15

WAS WBCs lack microvilli due to the lack of actin polymerization
cell surface projections require ability to reorganize actin based cytoskeleton

Question 16

why might a T cell respond to mitogen, but not to signaling via the T cell receptor using a recall antigen?

Answer 16

mitogen helps collect TCRs on surface via the stimulation of microtubules (no issues with these)
recall antigen doesn’t work because the TCR can’t be independently brought to the surface to recognize antigen due to a lack of actin polymerization in WAS patients

Question 17

which cell type is thought to be responsible for the development of autoimmunity in WAS patients?

Answer 17

Treg cells

Question 18

discuss the formation of the immune synapse

Answer 18

takes up to 10 min
can be sustained for several hours
requires reorganization of the actin and microtubule based cytoskeletons

Question 19

goal of the immune synapse

Answer 19

to provide long term, high quality signaling required for full T cell activations

Question 20

what is at the very center of the immune synapse/ supramolecular activation cluster (SMAC)

Answer 20

TCR:MHC antigen recognition

Question 21

what surrounds the TCR:MHC central region of the SMAC

Answer 21

CD28:CD80 costimulation

Question 22

what surrounds the CD28:CD80 region of the SMAC

Answer 22

LFA1:ICAM1 adhesion

Question 23

what is in the outermost region of the SMAC

Answer 23

F-actin lamellipodium, CD45, CD44, CD43 (larger molecules)

microclusters of CD28 and TCR

Question 24

what is the rationale for increased susceptibility to viral infections in WAS patients as it pertains to CD8+ T Cells?

Answer 24

immune synapse cannot form properly, this is needed for directed cell killing
T cell cannot move and release vesicles of granules

Question 25

how could WAS mutations affect NK cell function?

Answer 25

lack of reorganization of cytoskeleton to facilitate killing functions

Question 26

how could WAS mutations affect macrophage migration induced by a chemokine?

Answer 26

can’t migrate bc can’t reorganize cytoskeleton (thus no movement)

Question 27

how does WAS affect cytokine secretion?

Answer 27

cannot direct the release of cytokines to specific cells

Question 28

what would the lack of a thymic shadow on a CXR indicate?

Answer 28

lack of T cells, but normal B cell numbers

Question 29

why are Ig levels so low in X-linked SCID patients?

Answer 29

T cells cannot mature

without T cell help, B cells cannot be stimulated to make as many Igs