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Agonist/endogenous peptide–MHC heterodimers drive T cell activation and sensitivity


αβ T lymphocytes are able to detect even a single peptide–major histocompatibility complex (MHC) on the surface of an antigen-presenting cell1,2. This is despite clear evidence, at least with CD4+ T cells, that monomeric ligands are not stimulatory3,4. In an effort to understand how this remarkable sensitivity is achieved, we constructed soluble peptide–MHC heterodimers in which one peptide is an agonist and the other is one of the large number of endogenous peptide–MHCs displayed by presenting cells. We found that some specific combinations of these heterodimers can stimulate specific T cells in a CD4-dependent manner. This activation is severely impaired if the CD4-binding site on the agonist ligand is ablated, but the same mutation on an endogenous ligand has no effect. These data correlate well with analyses of lipid bilayers and cells presenting these ligands, and indicate that the basic unit of helper T cell activation is a heterodimer of agonist peptide– and endogenous peptide–MHC complexes, stabilized by CD4.

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Figure 1: Self-peptide–MHCs accumulate at the T cell–APC interface.
Figure 2: Soluble heterodimers of agonist and endogenous pMHCs can stimulate T cells.
Figure 3: Soluble heterodimers can trigger IL-2 production and stimulation by endogenous and agonist pMHC on cell surfaces and lipid bilayers.
Figure 4: T cell sensitivity to mutations affecting CD4 binding and a modified pseudodimer model of activation.


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We thank J. D. Stone and L. Stern for providing the crosslinker reagent to initiate these studies as well as for helpful discussions. We thank B. Lillemeier for Baculovirus DNA encoding His-tagged ICAM-1 and B7-1. We thank C. Schæfer-Nielsen, M. Kuhns, A. Krogsgaard and members of the Davis and Chien laboratory for helpful discussions. We thank K. C. Garcia and M. Winslow for critical reading of the manuscript and helpful discussions and analysis. We thank N. Prado and B. Smith for technical assistance. M.K. was a postdoctoral fellow of the Alfred Benzon Foundation and the Danish Medical Research Council. Q.L. and M.H. are supported by Helen Hay Whitney Foundation Fellowships. This work is supported by grants from the NIH and from the Howard Hughes Medical Institute.

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Correspondence to Mark M. Davis.

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Supplementary information

Supplementary Notes

This file contains legends to accompany Supplementary Figures S1-S7 and Supplementary Movies S1-S5. This file also contains Supplementary Methods and additional References. (DOC 35 kb)

Supplementary Figure S1

Accumulation analysis of endogenous/null MCC-derived peptides. (PDF 1712 kb)

Supplementary Figure S2

Binding and stability analysis of endogenous/null and MCC-derived peptides. (PDF 283 kb)

Supplementary Figure S3

Functional characterization of generated pMHC dimers. SDS-PAGE analysis and T-cell activation (Ca2+) analysis. (PDF 1781 kb)

Supplementary Figure S4

T-cell activation potency (Ca2+ and PI3K) and binding affinity of pMHC dimers. (PDF 358 kb)

Supplementary Figure S5

Effect of endogenous peptides when presented by membrane-associated MHC on the surface of CHO cells or in supported lipid bilayers. (PDF 360 kb)

Supplementary Figure S6

Effect on endogenous-agonist pMHC dimer induced T-cell activation by ablating CD4 binding with a CD4 blocking antibody or CD4 binding mutations. (PDF 216 kb)

Supplementary Figure S7

Effect on null-agonist pMHC dimer induced T-cell activation by ablating CD4 binding with CD4 binding mutations. (PDF 224 kb)

Supplementary Videos S1

Ca2+ response and PH(Akt)-YFP localization in 5C.C7 T cells in response to pMHC dimers. (MOV 416 kb)

Supplementary Videos S2 (MOV 545 kb)

Supplementary Videos S3 (MOV 597 kb)

Supplementary Videos S4 (MOV 458 kb)

Supplementary Videos S5 (MOV 308 kb)

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Krogsgaard, M., Li, Qj., Sumen, C. et al. Agonist/endogenous peptide–MHC heterodimers drive T cell activation and sensitivity. Nature 434, 238–243 (2005).

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