Recognition of Self vs' NonSelf

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Recognition of Self vs. Non-Self
ADAPTIVE
INNATE

• T cells, B cells
• Rearrangement of VDJ segments
• 400 million years old
• delayed response clonal expansion
• Memory

• Macrophages, Dendritic Cells, Neutrophils, Mast
  Cells, NK cells.
• Germline encoded receptors
• Evolutionarily ancient
• Immediate response
• No memory

Innate immune cells use germline-encoded pattern
recognition receptors to identify conserved
molecular patterns characteristic of
microbes. E.g. Toll-like Receptors Ligands
bacterial cell wall components
(lipopolysaccharide, lipoteichoic acid,
lipopeptides) flagellin (component of
bacterial flagella) dsRNA (characteristic of
some viruses) others
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(No Transcript)
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gd T cells
gd T cell production

• characteristic V segment usage in different
  tissues
• ligands? (differ from ab T cells - not
  peptide-MHC)
• host stress antigens
• prenyl pyrophosphates (human Vg2Vd2)
• T10/22 non-classical MHC (mouse)
• - mount rapid response

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• NK T cells
• small population of lymphocytes in most organs
• patrol liver sinusoids
• share characteristics of T cells and NK cells
• - have semi-invariant ab TCR
• Va14/Ja18 with TCRb with Vb2, Vb7 or Vb8 (in
  mouse)
• recognize glycolipid structures on
  (non-polymorphic) CD1d
• e.g. glycosphingolipid a-Gal-Cer from
  Sphingomonas bacteria
• glycolipid (diacylglycerol) from Borellia
• produce cytokines IL-2 -gt Tc activation
• IL-4 -gt Th2 differentiation
• IFNg -gt NK cell activation
• express CD40L -gt DC activation
• - immediately ready to perform effector functions
  (e.g. cytokine production)

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• NK Cells
• discovered in 1970s
• large, granular lymphocytes
• non-T, non-B (Ig-, CD3-) null cells
• develop in bone marrow
• can recognize and kill a wide variety of cells
• virus-infected cells
• tumour cells
• transplanted cells (especially bone marrow)
• antibody-coated cells
• stressed cells

Related to CTL similar killing mechanism
(perforin, granzyme) Also make cytokines (IFN-a
and TNFa) early in immune response important
for TH1 adaptive immunity
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Early, innate response
Activated by IFNs
- lytic response ready to go, like effector
CTLs - similar behaviour in primary and secondary
responses (no memory)
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How do NK cells recognize targets? One way is
Antibody-Dependent Cellular Cytotoxicity (ADCC)
Fc receptors also mediate phagocytosis of
antibody-coated particles by macrophages and
neutrophils
FcR
ITAM
macrophage
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Other mechanisms? (antibody-independent killing
also occurs)

• 1980s
• It was known
• - Many good NK cell targets (tumours,
  virus-infected cells) have low levels of MHC
  Class I (poorly recognized by T cells)
• Treatment of cells with IFNab -gt increased MHC I,
  decreased NK killing
• Hybrid resistance NK cells followed opposite
  rules to T cells

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Hybrid resistance
P1
X
MHCb
MHCa
skin transplant accepted (T cells tolerant to
MHCa, seen as self)
F1
ACCEPTED
MHCa/b
X
bone marrow transplant rejected by NK cells (due
to lack of MHCb)
MHCb
MHCa
REJECTED
MHCa/b
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Klas Kärre Missing Self Hypothesis NK
cells recognize the absence of self molecules,
including MHC Class I. Sources of inspiration
short sentences, Swedish submarines, and sea
squirts. Short Sentence (What do NK cells not
kill? Cells having high levels of a complete
set of autologous MHC I molecules.) Swedish
fisherman how do you recognize a foreign
submarine?
non-self
self
Sea Squirt (tunicate Botryllus) uses missing
self recognition of polymorphic self markers to
control self-fertilization
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Evidence supporting hypothesis 1) Kärre
selected tumours for loss of MHC I -gt became
sensitive to NK cell lysis. 2) Cells from
b2m-deficient mouse (no MHC I expression ) were
rejected when transplanted into syngeneic mouse,
because of NK cell killing. 3) RMA tumour cells
derived from B6 mouse (H-2b) D8 an H-2Dd
transgenic B6 mouse (expresses H-2Db and
H-2Dd) RMA cells are resistant to NK killing if
injected into a B6 mouse sensitive to NK
killing if injected into a D8 mouse
Db
Db
tumor grows (NK cell dont kill)
B6
RMA
Db,Dd
benign (NK cells kill)
D8
(Implies NK cells in D8 are educated during
development to recognize H-2Dd as self seen as
missing in RMA -gt killing)
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NK vs T cell recognition of MHC opposite effects
nude mice no T cells, but increased NK cells
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Missing self recognition implies existence of
inhibitory receptors. NK cells express both
stimulatory and inhibitory receptors. Stimulatory
receptors - some recognize ligands that are
on most self cells mediate binding of NK to
target - some recognize ligands that are
upregulated on cells during infection or
tumorigenesis Inhibitory receptors - some
recognize MHC-I - some recognize non-MHC ligands
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NK Cell activation is determined by a balance
between positive and negative signaling
Normal Cell Protected
upregulation of stimulatory ligands
loss of inhibitory ligands
KILL!
KILL!
stimulatory ligand
MHC I
stimulatory receptor
inhibitory receptor
-
-
NK Cell
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Identification of an inhibitory
receptor Anti-Ly49A mAb developed
found different subsets
Kill
H-2Dd
incubation with anti-Ly49A or anti-H-2Dd allows
killing by Ly49A cells (disinhibited)
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NK Receptors genomic organization
Lectin-like
Ig-like
Mouse chr. 7
a c d f
d e a c
Mouse chr. 6
CD69
CD94
NKp46
Ly49
NKG2
NKRP1
PIR
Human chr. 19
D F E C A
LAIR
CD69
Human chr. 12
NKRP1A
Ly49L
NKp46
KIR
NKG2
CD94
ILT/LIR
ILT/LIR
Natural killer gene complex (NKC)
Leukocyte receptor complex (LRC)
Rapidly evolving loci (e.g. inhibitory
MHC-binding receptors horses mainly Ly49
cattle mainly KIR)
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Receptors Ligands human
mouse KIR/Ly49 Inhibitory MHC Ia HLA-A,
B, C H2-D,K,L KIR/Ly49 Activating
MHCIa? decoy receptors ? CD94/NKG2A Inhibitory
MHC Ib HLA-E
Qa1b CD94/NKG2C Activating
(peptides from leader seqs. of MHC-Ia !
) NKG2D Activating Oncofetal Ags
ULBP, MICA Rae-1 NKRP1B Inhibitory
Ocil/Clr CD16 Activating
IgG others.
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KIR and Ly49 inhibitory receptors (structurall
y unrelated convergent evolution)
KIR (humans) Ig domains
Ly49 (mouse) C-type Lectin-like

• Similarities
• small gene families (10-15) that have
  diversified by gene conversion
• substantial polymorphism in population
• expressed on subsets of NK cells stochastic
  control shaped by host MHC haplotype
• inhibitory members contain ITIMs
• recognize polymorphic determinants on MHC
  Class I

ITIM
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Inhibitory receptors are subset-restricted
-gt the NK cell population can detect loss of
individual inhibitory ligands
e.g.
KILL!
loss of Kd
Dd
Dd
Kd,Dd
Kd
-
-
-
NK-1
NK-1
NK-2
NK-2
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Activating
CD16
NKG2D
NKG2C/CD94
NKR-P1C
-
-
-

-



-


-
-
FcRg
FcRg
DAP12
DAP12
ITAM
ITAMs recruit Syk/ZAP70 -gt activation
Inhibitory
NKG2A/CD94
NKR-P1B
KIR
Ly49
ITIM
ITIMs recruit phosphatases (SHP1,SHP2, SHIP-1) -gt
antagonize ITAM-mediated activation
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There are also activating KIR and Ly49 family
members. Function? One possibility (suggested
by Lanier) - chasing pathogen decoy
receptors Ly49I inhibitory receptor, target of
MCMV m157 protein Ly49H activating,
resistance factor against MCMV Possible
evolutionary sequence of events
pathogen evolves decoy MHC mimic
self MHC
inhibitory Receptor
self MHC
decoy MHC
e.g. MCMV m157
activating
ITIM
decoy MHC
lose affinity for self MHC gain affinity for
pathogen-derived product gene conversion to gain
ITAM, become activating
ITAM