Jonathan R. Lamb

Structural model of HLA-DR1 restricted T cell antigen recognition

Two human helper T cell determinants in influenza have been identified, one in the hemagglutinin and the other in the matrix protein (M1). Both were shown to be DR1 restricted by using transfected L cells to present antigen. Comparison of the sequences of the two peptides revealed a similar pattern that could account for their DR1 specificity if the peptides adopt a helical conformation. The model was supported by the demonstration that hybrid peptides, composed of the amino acids that interact with DR1 from one determinant and the residues that interact with the T cell receptor from the other, were recognized by each clone. The generality of the motif was confirmed by the finding that DR1 individuals respond to a ragweed peptide containing the defined pattern.

The 65kDa antigen of mycobacteria-a common bacterial protein?

The 65 kilodalton antigen of Mycobacterium tuberculosis and M. leprae is a well-characterized, strongly immunogenic protein eliciting antibody and T-cell responses in infected patients. Recent studies have disclosed regions of cross-reactivity between the 65kDa antigen and proteins in many other bacterial species. These include the product of the ams gene in E. coli which is involved in the processing of RNA. Here Douglas Young and his colleagues discuss these observations, the significance of the 65kDa antigen and its possible role in the pathogenesis of mycobacterial and other diseases.

The use of nitrocellulose immunoblots for the analysis of antigen recognition by T lymphocytes

Antigen insolubilised on nitrocellulose is able to activate T lymphocytes following presentation by appropriate accessory cells. Furthermore, complex mixtures of antigens can be fractionated by polyacrylamide gel electrophoresis under denaturing conditions (SDS-PAGE), transferred to nitrocellulose membranes and then added to T cell proliferation assays. This allows a direct screening for recognition of individual polypeptides by monoclonal and polyclonal T cell populations, without a requirement for extensive biochemical purification and in the absence of initial serological preselection of antigen. The potential use of this technique for screening of recombinant DNA libraries for expression of antigens recognised by T cells is also illustrated. The technical aspects of T cell recognition of solid-phase antigen and its application to the identification of immunodominant epitopes with the potential to modulate T cell-mediated immunity is reviewed.

The mycobacterial Groel stress protein: a common target of T-cell recognition in infection and autoimmunity

The 65 kD protein of mycobacteria is an immunodominant antigen for both T and B lymphocytes. Sequence analysis has revealed that this protein belongs to the highly conserved family of stress proteins, related to the GroEL gene product of E. coli, that are present in all cells from bacteria to man. We demonstrate here that human T cells from healthy individuals and disease sites are able to recognize determinants within the 65 kD protein that are either specific for M. tuberculosis or are conserved between GroEL of mycobacterial, E. coli or human origin. The induction of T cells that recognize with cross-reactive sequences of GroEL may provide an explanation for the autoimmune phenomena often associated with infection by microbial pathogens. However, both the magnitude and the biological significance of this component of the T-cell repertoire reactive with self stress proteins will be influenced by local environmental factors as well as the MHC haplotype of the individual.

Clonal Analysis of the Cellular Immune Response to the House Dust Mite Dermatophagoides farinae

A panel of human CD4+ T cell clones specific for the house dust mite was isolated from an atopic individual with perennial rhinitis. Soluble antigen specificity was defined using proliferation assays and subsequently the antigenic determinants recognized by some of these clones were mapped using nitrocellulose immunoblots of fractionated Dermatophagoides spp. Both cross-reactive and species-specific T cell clones were identified and in some instances their specificity could be mapped to the serologically defined Der f I, Der p I and Der f II allergens. In comparison, the serum antibody response showed additional specificity for Der f III. The antigen recognition by six of these clones was found to be restricted by HLA-DR gene products.

p145-MR6: A Novel T Cell Surface Molecule with a Role in Tolerance to Self

The role of the thymus in the generation of the T cell repertoire is well established (Gelfand et al., 1980; Cantor and Weissman, 1976), but remains poorly understood. In order to study the molecular influences within the microenvironment of the thymus we raised monoclonal antibodies to the stromal components of the thymic microenvironment as described previously (DeMaagd et al., 1985; Ritter et al., 1985). This study focuses on one such antibody, MR6, which reacts strongly with the cortical epithelium and medullary macrophage/dendritic cells (MO/DC), and less strongly with thymocytes and T cells (Larche et al., 1987). Functional studies on this molecule (pl45-MR6) lead us to believe that it may play a central role in the clonal “deletion ” of autoreactive T cells within the thymus.

Studies of MHC Class II Restricted Antigen Recognition by Human T Cell Clones Using Transfectant Antigen-Presenting Cells (APC)

Using transfected L-cell antigen-presenting cells (APC) and synthetic peptides of antigen, the recognition of antigen/MHC by two DR1-restricted T-cell clones, specific for hemagglutinin and matrix protein determinants of influenza A, was examined. Transfectants expressing DR1 functioned as efficient APC for both T-cell clones. The substitution of I-Eα for DRα led to no loss of antigen sensitivity, and the matrix protein-specific clone also gave an antigen-dependent response in the context of I-Eβk:I-Eα. If the amino-terminal domains of DR1 and I-Ek are modeled on the three-dimensional structure of the α1 and α2 domains of HLA-A2, it is striking that almost all the α1 residues that differ between DR and I-E fall outside the putative antigen-binding groove. The β1, domains of DR1 and I-Ek have multiple differences throughout the domain, however, the residues in the bm12 region are significantly conserved. Comparison of the sequences of antigenic peptides that are co-recognized with DR1 and I-Ek reveals four residues with conserved features, spaced 1,4,5, and 8. These four residues can be exchanged between the hemagglutinin and matrix protein peptides without loss of specific recognition. These results suggest that the antigen-binding sites of DR1 and I-Ek are similar, and that the four residues with conserved features that can be exchanged between the two peptides may form one face of an α-helix and contribute to the DR1: antigen interaction.

Recognition of the HLA Class II-Peptide Complex by T cell Receptor: Reversal of MHC Restriction of a T Cell Clone by a Point Mutation in the Peptide Determinant

The recent demonstration that peptide fragments of immunogenic proteins are bound by MHC class II molecules has provided an important explanation for the genetic basis of immune responsiveness (Babbitt et al. 1985; Guillet et al. 1987; Buus et al. 1986). Although not the sole factor, the formation of a peptide-MHC complex appears to be a necessary requirement for both the generation of a cellular immune response and the T cell-dependent humoral response (reviewed by Moller 1987). Even though these experiments have generated a unified model of T cell recognition, not all issues have been resolved. One confusing is if binding to one of an individual’s MHC proteins is critical to the generation of an immune response and subsequent protection from infection, how can a very limited number of binding sites interact with a sufficiently large percentage of peptides from the multitude of proteins from pathogens to protect the individual? The ability of an MHC protein to interact with manifold peptides is quite different from the specificity characteristic of other known membrane receptors. In contrast with receptors of the endocrine system, which have evolved to optimize their specific interaction with ligand, the MHC proteins appear to have developed to bind a diverse range of ligands.

Structure and Expression of Genes Involved in T Lymphocyte Recognition and Activation

Human T lymphocytes can be activated by two apparently distinct pathways. The first pathway is mediated through the T cell receptor (TcR) complex following corecognition of antigen and major histocompatibility complex (MHC) gene products (Reinherz et. al., 1982). The TcR complex comprises an αβ heterodimer (Ti) which is linked non-covalently to a non-polymorphic glycoprotein, the CD3 antigen (see Kronenberg et al., 1986 for a review). The CD3 antigen in turn comprises at least three polypeptide chains, γ, δ and e (Borst et al., 1983; Kanellopoulos et al., 1983). The αβ heterodimer is sufficient to confer clonal variability in the recognition of antigen/MHC to a T cell (Dembic et al., 1986). The CD3 antigen, which is obligatorily expressed with the αβ heterodimer (or with TcR γ chains: see Brenner et al., 1986; Bank et al., 1986) has been implicated in the signal transfer process consequent to specific binding of a T cell to a target cell or antigen presenting cell. Several events have been implicated in the signal transfer process, including phosphorylation of the CD3 γ chain, increased phosphatidyl inositol bis phosphate turnover and downregulation of the TcR complex from the cell surface (Weiss et al., 1984; Cantrell et al., 1985; Davies et al., 1985; Imboden et al., 1985).