I. ?? T Cells II. Invariant TCR T Cells

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I. ?? T Cells II. Invariant TCR T Cells
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?? T Cells in Autoimmune and Infectious Disease

• ?? T cells can account for 30 of the T cell
  infiltrate in MS lesions (Wucherpfennig, K. W.,
  et. al. PNAS 894588).
• ?? T cells expand from 5 to 17 of PBMCs in
  patients during acute stages of P. Falciparum
  (Ho, M. et. al. Infect Immun. 62 855862).
• Similar ?? T cell expansion has been observed in
  M. Tuberculosis infection and Chrons disease.

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?? KO Mice Reveal a Unique role for Gamma Delta T
Cells

• Infections agents can be lethal

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Gram-positive Nocardia asteroides Causes Lethal
Infection in ?? T Cell KO Mice

Tam et. al., Infection Immunity, 2001 696165.
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Lung Sections of Mice Infected with Aerosolized
Gram-positive N. asteroides
?-/- KO
B6
? Neutrophils in ?-/- mice
N. asteroides (dark blue stain)
Tam et. al., Infection Immunity, 2001 696165.
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?? KO mice reveal a unique role for Gamma Delta T
cells

• Certain infections can be lethal.
• Most infections reveal inflammatory defects in ??
  KO mice.
• Pathological outcome is different than that of ??
  KO micewhich usually die upon infectious
  challenge.
• Skin wound healing is impaired.

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?? T Cells Distribute Differently Then ?? T Cells

• Anatomically located lining the epithelial
  tissues
• Small numbers (1-2 of cells) found in the
  lymphoid tissues, spleen and lymph nodes
• ?? might play a role early in the immune response

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What do Gamma Delta TCRs recognize?
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CDR3 Length Distribution of Immune Receptor Chains
B cell receptor
?? T cell receptor
MHC
?? T cell receptor
?
Ed Rock, et. al.
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What do Gamma Delta TCRs recognize?

• MHC class II, IEk.

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LBK5 ?? T cell clone recognizes backbone
residues of class II IEk and recognition is
independent of the presented peptide.
Important residues for LBK5 stimulation
LBK5 was generated from immunization with
non-MHC matched splenocytes.
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Significance of IEk Recognition?

• Unlike MHC restricted ?? T cell clones, peptide
  does not confer reactivity of LBK5 to IEk.
• Gamma delta T cells recognize antigens in a
  fundamentally different way than ?? T cells.
• Gamma delta development seems to be normal in
  b2m-/- and MHC II negative mice, which suggest
  that the many of the ?? TCR ligands are not
  conventional MHC molecules.

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What do Gamma Delta TCRs Recognize?

• MHC class II, IEk
• HSV-gI envelope protein

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HSV-1
gI envelope protein is left on the cell surface
Viral DNA
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TgI4 ?? T Cell Clone is Stimulated by Plate
Bound HSV-gI Protein
Cell lysis blocked by ?-TCR and ?-gI mAbs.
TgI4 was recovered from mice inoculated (I.V.)
with HSV-1.
Sciammas, R. et. al. J. Exp. Med 1851969
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Significance of HSV-gI Interaction?

• Like B cell Ig receptors, ?? TCRs can recognize
  protein directly without need for processing and
  presentation upon MHC molecules.

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HSV-1
gI envelope protein is left on the cell surface
Viral cDNA
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What do Gamma Delta TCRs Recognize?

• MHC class II, IEk
• gI HSV envelope protein
• Non-classical MHC T22/T10

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T22 Tetramer Binds High Frequencies of ?? T Cells
Non-immunized mice
T22 tetramer

• T22 cant present antigens because of its
  truncated MHC ? barrel.
• T22 is upregulated on APCs upon CFA immunization
  or LPS stimulation.
• Affinity measurements can be made between G8 ??
  TCR and T22.

?? TCR
Crowley, M. et. al. Science 2000, 287314
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Significance of T22 Recognition?

• Self or natural ligand
• This ligand is not recognized by ?? TCRs,
  suggesting that the ?? TCR recognize
  non-overlapping cues through the ?? TCR.

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Significance of T22 Recognition?
T cell Status of immune system Frequency1 T10/T22
- specific gd T cells 1/250 MHC/peptide
specific ab T cells (not primed)
1/1,000,000 MHC/peptide specific ab T
cells (Immunized effector phase) 1/2-1/100

High frequencies fast immune responses to
ligand
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What do Gamma Delta TCRs recognize?

• MHC class II, IEk
• gI HSV envelope protein
• Non-classical MHC T22/T10
• Small phosphate antigens

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Small Alkyl-Phosphate Antigens are Secreted by
Bacteria and Also Expressed in Mammalian Tissues.

• Small phosphate antigens stimulate human and
  monkey V?2 V?2 T cells (Shen, Science,
  2952255-8).
• V?2 V?2 T cells expand (15-60) in response to a
  variety of infectious agents.
• Reactivity is mediated through the ?? TCR and the
  CDR3 is important for reactivity (Bukowski, J. I.
  161286)
• Cell contact is required (Morita, Immunity
  3495).
• No processing is required (fixed cells small
  phosphate antigen stimulation) (Morita,
  Immunity 3495).

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Significance of Small Phosphate ?? TCR
Recognition?

• Ligands can either be self or foreign.
• Small phosphates are produced by the nucleotide
  salvage pathway, during cellular stress (i.e.
  heat shock, starvation, etc.) (Constant, P.
  Science 264267).
• Suggesting that ?? T cells monitor cellular
  stress.

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Other Reports of ?? TCR Ligands

• MICA a non classical MHC that is upregulated on
  tumor cells and upon heat shock (Wu, J. et. al.
  J. I. 1691236).
• CD1c- No addition of antigen is required (Spada F
  et. al. JEM March 2000).
• Hsp60 has been reported to be stimulatory.
• Qa-1b can stimulate ?? T cells.

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?? T Cell Summary

• ?? T cells can recognize self (MHC and MHC-like)
  and foreign ligands (HSV-gI, small phosphate
  antigens).
• Many of the ligands are up regulated on the
  surface of cells upon infection or stress.
• Taken together ?? T cells might see cell
  surface perturbations in homeostasis through
  their TCR and regulate the immune response.

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LPS
Cell
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II. Invariant TCR T cells.

• Invariant TCR T cells clonally/oligoclonally
  express TCRs with a limited P/N/Junctional CDR3
  diversity.
• High frequencies are found in specific tissues.
• NK T cells, DETC ?? T cells, MAIT cells.

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Invariant NK T cells (iNK T cells)

• Defined as being reactive to CD1d.
• Express the invariant V? and limited V? TCRs.
• iNK T cells represent the majority of T cells
  found in the liver.
• 1-3 found in the spleen.
• Express markers found on NK cells.

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V? TCR sequences of CD1d restricted iNK T cells
Lantz, O. and Bendelac, A., J. Exp. Med.
1801097, 1994.
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What do the iNK T cells recognize?

• CD1d plus.
• An unidentified endogenous self-glycolipid
  antigen.

• ?-GlcCer synthase KO APCs fail to stimulate
  galcer/CD1d1 restricted NK T cells (Stanic et al.
  PNAS, 2003).
• Selected by CD1, CD8, CD4, positive cells in the
  thymus (Nat Immunol. 2971).

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?-Galactosylceramide and iNK T cells

• CD1 family of B2m dependent class Ib proteins
  that can present a variety of lipid antigens to
  CD1 restricted T cells.
• 80 of NK T cells (NK1.1) in both mouse and
  human express an invariant TCR (mV?14-J?281,
  hV?24-J?Q) that recognize CD1d loaded with
  ?-GalCer.
• Mammalians do not synthesize ?-GalCer which is
  derived from sea sponges.

?-Galcer is likely a structural mimic of a self
or natural ligand.
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iNK T cells are specific for CD1d1 ?-Galcer
Loaded with a-Galcer
Not preloaded
CD1d tetramer
TCR ?
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iNK T cell function

• Rapidly (within 1-2 hours) secrete IFN-? and/or
  IL-4 upon stimulation in vivo (Yoshimoto T J.
  Exp. Med. 1791285).
• J?281-/- mice lack iNK T cells and have delayed
  immune responses to a variety of infectious
  agents.

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Dendritic Epidermal ?? T cells (DETCs) promote
wound healing
?-/-
B6
Jameson et. al. Science 296747
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What is the DETC TCR ligand?

• We dont know.
• Heat shocked keratinocytes stimulate DETC cells
  in a TCR dependent fashion (Haravan, W. Science
  2521430).
• This ligand is not sensitive to trypsin treatment
  (unpublished results), therefore is most likely
  not a protein.

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Table summarizing invariant T cell phenotypes
Cell Conserved in Mouse and Man? iTCR (mouse) Development is dependent upon Ligand Location Auto-reactive Negatively selected?
NK T Yes Va14-Ja281 CD4,CD8, CD1 Thymocytes ? (similar to a-Galcer) Liver, Spleen Yes ?(No in most models)
MAIT Yes Va19-Ja33 B cells, MR1, Microbial Flora ? Gut Lamina Propria Yes ?
DETC No Vg5 Vd1 Conformationally dependent fetal TCR expression ? (not a protein) Skin Yes ? (Yes, in some models)
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First line of Defense

• Invariant and gamma delta T cells respond quickly
  to antigenic stimulus.
• Should these T cells be classified as being apart
  of the innate immune system or not?