Tom Cotner

Factors governing the binding and recognition of foreign and self-peptides by MHC class II

Considerable progress has been made in understanding the basis of T cell recognition and T cell activation. This knowledge has recently been used to modulate T cell activation in animal models of experimental autoimmune disease by two means--selective MHC blockade and peptide-induced tolerance. The use of peptides to interfere with the binding of autoantigenic peptides to MHC requires knowledge of both the class II allele which presents the immunodominant peptide to autoimmune T cells and the identification of peptide analogs that bind with high affinity to that allele. The alternative strategy of peptide-induced tolerance will require identification of the autoantigen and its immunodominant peptides. While the latter approach holds great promise for immunointervention, its wide application will require full knowledge of the mechanisms by which tolerance to self is maintained and how it can be broken.

The Role of HLA-DM in Class II Antigen Presentation

The major histocompatibility complex (MHC) class I and class II molecules serve as peptide receptors which present antigenic peptide complexes to T cells. The presentation of antigen to T cells requires that the antigens first be processed prior to presentation. Peptide binding occurs intracellularly and MHC class I and class II molecules bind peptides derived from different cellular locations: peptides derived from mainly cytoplasmic sources bind to class I whereas proteins taken up from the extracellular environment are degraded and bind to class II.

Characterization of Multiple HLA-DR3 Haplotypes

The HLA-DR allospecificities, DR1-DRw14, are defined by using selected alloantisera. Analysis at the biochemical and molecular level has demonstrated DRs structural heterogeneity within certain haplotypes such as DR2, DR4, and DRw8 (1–4). Although DR3 is well defined (5), a recent variant has been described at the biochemical and molecular level (6,7). Here we describe three DR3 subtypes that can be distinguished by a combination of two-dimensional gel electrophoresis, monoclonal antibody (MAb) reactivity, quantitative variation in expression, and reactivity with DRw52-specific T-cell clones.

Functional Analysis of HLA-DR3: A Mutational Approach

Class II mutant B lymphoblastoid cell lines (B-LCL) affected in presentation of soluble antigen to HLArestricted antigen-specific T cells can be used to characterize the molecular interactions involved in antigen presentation. We have isolated class II mutants in the DR3 haplotype, a haplotype of particular interest because of its association with several autoimmune diseases (1). Here, we describe the use of antigen loss mutants to localize restriction elements to the DRβ1, DRβ3, and non-DR dimers of the DR3 haplotype, and the use of mutants expressing altered DR3 molecules to identify regions of DR3 molecules involved in antigen presentation and in α/β chain association.