A role for the region encompassing the c" strand of a TCR V alpha domain in T cell activation events

T cell recognition of distinct peptide:I-Au conformers in murine experimental autoimmune encephalomyelitis

We have used T cells bearing TCRs that are closely related in sequence as probes to detect conformational variants of peptide-MHC complexes in murine experimental autoimmune encephalomyelitis in H-2(u) mice. The N-terminal epitope of myelin basic protein (MBP) is immunodominant in this model. Our studies have primarily focused on T cell recognition of a position 4 analog of this peptide (MBP1-9[4Y]) complexed with I-A(u). Using site-directed mutagenesis, we have mapped the functionally important complementarity determining region residues of the 1934.4 TCR Valpha domain. One of the resulting mutants (Tyr(95) to alanine in CDR3alpha, Y95A) has interesting properties: relative to the parent wild-type TCR, this mutant poorly recognizes Ag complexes generated by pulsing professional APCs (PL-8 cells) with MBP1-9[4Y] while retaining recognition of MBP1-9[4Y]-pulsed unconventional APCs or insect cell-expressed complexes of I-A(u) containing tethered MBP1-9[4Y]. Insect cell expression of recombinant I-A(u) with covalently tethered class II-associated invariant chain peptide or other peptides which bind relatively weakly, followed by proteolytic cleavage of the peptide linker and replacement by MBP1-9[4Y] in vitro, results in complexes that resemble peptide-pulsed PL-8 cells. Therefore, the distinct conformers can be produced in recombinant form. T cells that can distinguish these two conformers can also be generated by the immunization of H-2(u) mice, indicating that differential recognition of the conformers is observed for responding T cells in vivo. These studies have relevance to understanding the molecular details of T cell recognition in murine experimental autoimmune encephalomyelitis. They are also of particular importance for the effective use of multimeric peptide-MHC complexes to characterize the properties of Ag-specific T cells.

Activation of a T cell hybridoma by an alloligand results in differential effects on IL-2 secretion and activation-induced cell death

The molecular nature of the interaction of T cell receptors (TCR) with alloligands is not well understood. Although a role for groove-bound peptide(s) has been clearly demonstrated for major histocompatibility complex (MHC) class I alloreactivity, this has not been established for MHC class II-induced alloresponses. In the present study, we have analyzed the interaction of a nominal peptide-self MHC complex and of an alloligand with their cognate TCR (1934.4 TCR for autoantigen recognition and qCII85.33 TCR for allorecognition). Our results demonstrate that 1934.4 TCR recognition of the N-terminal epitope of myelin basic protein (Ac1-11, Ac=acetylated at position 1) complexed with the MHC class II molecule I-A(u) involves contacts with both chains of the MHC molecule. In contrast, qCII85.33 TCR recognition of an allopeptide:I-A(u) complex appears to predominantly involve the beta chain of the MHC molecule. Thus, the two TCR appear to have different footprints on the I-A(u) molecules. Unexpectedly, this differential involvement of the two chains of the I-A(u) molecule affects activation induced cell death, with allostimulation resulting in poor induction of FasL expression and relatively low levels of apoptosis. Significantly, stimulation of cognate T cells with alloantigen or autoantigen results in similar levels of IL-2 secretion. The reduced apoptosis of T cells in response to allostimulation may be one of the mechanisms that favors the expansion of a relatively large repertoire of alloreactive T cells.

Crystal structure of a T cell receptor Valpha11 (AV11S5) domain: new canonical forms for the first and second complementarity determining regions

We describe the X-ray crystallographic structure of a murine T cell receptor (TCR) Valpha domain ("Valpha85.33"; AV11S5-AJ17) to 1.85 A resolution. The Valpha85.33 domain is derived from a TCR that recognizes a type II collagen peptide associated with the murine major histocompatibility complex (MHC) class II molecule, I-A(q). Valpha85.33 packs as a Valpha-Valpha homodimer with a highly symmetric monomer-monomer interface. The first and second complementarity determining regions (CDR1 and CDR2) of this Valpha are shorter than the CDRs corresponding to the majority of other Valpha gene families, and three-dimensional structures of CDRs of these lengths have not been described previously. The CDR1 and CDR2 therefore represent new canonical forms that could serve as templates for AV11 family members. CDR3 of the Valpha85.33 domain is highly flexible and this is consistent with plasticity of this region of the TCR. The fourth hypervariable loop (HV4alpha) of AV11 and AV10 family members is one residue longer than that of other HV4alpha regions and shows a high degree of flexibility. The increase in length results in a distinct disposition of the conserved residue Lys68, which has been shown in other studies to play a role in antigen recognition. The X-ray structure of Valpha85.33 extends the database of canonical forms for CDR1 and CDR2, and has implications for antigen recognition by TCRs that contain related Valpha domains.

Kinetics and thermodynamics of T cell receptor- autoantigen interactions in murine experimental autoimmune encephalomyelitis

In the current study, cellular and molecular approaches have been used to analyze the biophysical nature of T cell receptor (TCR)-peptide MHC (pMHC) interactions for two autoreactive TCRs. These two TCRs recognize the N-terminal epitope of myelin basic protein (MBP1-11) bound to the MHC class II protein, I-A(u), and are associated with murine experimental autoimmune encephalomyelitis. Mice transgenic for the TCRs have been generated and characterized in other laboratories. These analyses indicate that the mice either develop encephalomyelitis spontaneously (172.10 TCR) or only if immunized with autoantigen in adjuvant (1934.4 TCR). Here, we show that the 172.10 TCR binds MBP1-11:I-A(u) with a 4-5-fold higher affinity than the 1934.4 TCR. Consistent with the higher affinity, 172.10 T hybridoma cells are significantly more responsive to autoantigen than 1934.4 cells. The interaction of the 172.10 TCR with cognate ligand is more entropically unfavorable than that of the 1934.4 TCR, indicating that the 172.10 TCR undergoes greater conformational rearrangements upon ligand binding. The studies therefore suggest a correlation between the strength and plasticity of a TCR-pMHC interaction and the frequency of spontaneous disease in the corresponding TCR transgenic mice. The comparative analysis of these two TCRs has implications for understanding autoreactive T cell recognition and activation.