Biomedical subjects

Sarah L Hutchinson

Publications and source records attributed to Sarah L Hutchinson.

4 recordsLinked to original sources

PubMed2005

Interaction between the CD8 coreceptor and major histocompatibility complex class I stabilizes T cell receptor-antigen complexes at the cell surface.

The off-rate (k(off)) of the T cell receptor (TCR)/peptide-major histocompatibility complex class I (pMHCI) interaction, and hence its half-life, is the principal kinetic feature that determines the biological outcome of TCR ligation. However, it is unclear whether the CD8 coreceptor, which binds pMHCI at a distinct site, influences this parameter. Although biophysical studies with soluble proteins show that TCR and CD8 do not bind cooperatively to pMHCI, accumulating evidence suggests that TCR associates with CD8 on the T cell surface. Here, we titrated and quantified the contribution of CD8 to TCR/pMHCI dissociation in membrane-constrained interactions using a panel of engineered pMHCI mutants that retain faithful TCR interactions but exhibit a spectrum of affinities for CD8 of >1,000-fold. Data modeling generates a "stabilization factor" that preferentially increases the predicted TCR triggering rate for low affinity pMHCI ligands, thereby suggesting an important role for CD8 in the phenomenon of T cell cross-reactivity.

Antigens↗

PubMed2003

Anti-CD8 antibodies can inhibit or enhance peptide-MHC class I (pMHCI) multimer binding: this is paralleled by their effects on CTL activation and occurs in the absence of an interaction between pMHCI and CD8 on the cell surface.

Cytotoxic T lymphocytes recognize short peptides presented in association with MHC class I (MHCI) molecules on the surface of target cells. The Ag specificity of T lymphocytes is conferred by the TCR, but invariable regions of the peptide-MHCI (pMHCI) molecule also interact with the cell surface glycoprotein CD8. The distinct binding sites for CD8 and the TCR allow pMHCI to be bound simultaneously by both molecules. Even before it was established that the TCR recognized pMHCI, it was shown that CTL exhibit clonal heterogeneity in their ability to activate in the presence of anti-CD8 Abs. These Ab-based studies have since been interpreted in the context of the interaction between pMHCI and CD8 and have recently been extended to show that anti-CD8 Ab can affect the cell surface binding of multimerized pMHCI Ags. In this study, we examine the role of CD8 further using point-mutated pMHCI Ag and show that anti-CD8 Abs can either enhance or inhibit the activation of CTL and the stable cell surface binding of multimerized pMHCI, regardless of whether there is a pMHCI/CD8 interaction. We further demonstrate that multimerized pMHCI Ag can recruit CD8 in the absence of a pMHCI/CD8 interaction and that anti-CD8 Abs can generate an intracellular activation signal resulting in CTL effector function. These results question many previous assumptions as to how anti-CD8 Abs must function and indicate that CD8 has multiple roles in CTL activation that are not necessarily dependent on an interaction with pMHCI.

Adjuvants, Immunologic↗

PubMed2003

The CD8 T cell coreceptor exhibits disproportionate biological activity at extremely low binding affinities.

T lymphocytes recognize peptides presented in the context of major histocompatibility complex (MHC) molecules on the surface of antigen presenting cells. Recognition specificity is determined by the alphabeta T cell receptor (TCR). The T lymphocyte surface glycoproteins CD8 and CD4 enhance T cell antigen recognition by binding to MHC class I and class II molecules, respectively. Biophysical measurements have determined that equilibrium binding of the TCR with natural agonist peptide-MHC (pMHC) complexes occurs with KD values of 1-50 microm. The pMHCI/CD8 and pMHCII/CD4 interactions are significantly weaker than this (KD >100 microm), and the relative roles of TCR/pMHC and pMHC/coreceptor affinity in T cell activation remain controversial. Here, we engineer mutations in the MHCI heavy chain and beta2-microglobulin that further reduce or abolish the pMHCI/CD8 interaction to probe the significance of pMHC/coreceptor affinity in T cell activation. We demonstrate that the pMHCI/CD8 coreceptor interaction retains the vast majority of its biological activity at affinities that are reduced by over 15-fold (KD > 2 mm). In contrast to previous reports, we observe that the weak interaction between HLA A68 and CD8, which falls within this spectrum of reduced affinities, retains substantial functional activity. These findings are discussed in the context of current concepts of coreceptor dependence and the mechanism by which TCR coreceptors facilitate T cell activation.

Antigen Presentation↗

PubMed2002

Novel CD8+ T cell antagonists based on beta 2-microglobulin.

The CD8 coreceptor of cytotoxic T lymphocytes binds to a conserved region of major histocompatibility complex class I molecules during recognition of peptide-major histocompatibility complex (MHC) class I antigens on the surface of target cells. This event is central to the activation of cytotoxic T lymphocyte (CTL) effector functions. The contribution of the MHC complex class I light chain, beta(2)-microglobulin, to CD8alphaalpha binding is relatively small and is mediated mainly through the lysine residue at position 58. Despite this, using molecular modeling, we predict that its mutation should have a dramatic effect on CD8alphaalpha binding. The predictions are confirmed using surface plasmon resonance binding studies and human CTL activation assays. Surprisingly, the charge-reversing mutation, Lys(58) --> Glu, enhances beta(2)m-MHC class I heavy chain interactions. This mutation also significantly reduces CD8alphaalpha binding and is a potent antagonist of CTL activation. These results suggest a novel approach to CTL-specific therapeutic immunosuppression.

Amino Acid Sequence↗