Point mutations define positions in HLA-DR3 molecules that affect antigen presentation.
Allelic differences in major histocompatibility complex (MHC)-encoded class II molecules affect both the binding of immunogenic peptides to class II molecules and the recognition of MHC molecule-peptide complexes by T cells. As yet, there has been no extensive mapping of these functions to the fine structure of human class II molecules. To determine sites on the HLA-DR3 molecule involved in antigen presentation to T cells, we used monoclonal antibodies specific for HLA-DR3 to immunoselect mutants of a B-lymphoblastoid line. We located the sites of single amino acid substitutions in the HLA-DR3 molecule and correlated these structural changes with patterns of recognition by HLA-DR3-restricted, antigen-specific T cells, allospecific T cells, and allospecific anti-DR3 monoclonal antibodies. We analyzed seven mutations. One mutation, at position 74 in domain 1 of the DR beta chain, affected recognition by all T cells tested, whereas others, at positions 9, 45, 73, 151, and 204 of the DR beta chain and position 115 of the DR alpha chain, altered recognition by some T cells, but not others. Each of the substitutions resulted in a unique pattern of T-cell stimulation. In addition, each T-cell clone recognized a different subset of the mutants. These results indicate that different residues of the DR3 molecule are involved in presentation of antigen to different DR3-restricted T cells. These studies further show that substitutions which most likely affect peptide binding alter recognition of DR3 molecules by an alloreactive T-cell clone and some allospecific antibodies.
Mellins
E
E
Department of Pediatrics, University of Washington, Seattle 98195.
Arp
B
B
Singh
D
D
Carreno
B
B
Smith
L
L
Johnson
A H
AH
Pious
D
D
D000483:Alleles; D000938:Antigen-Presenting Cells / Q000276:immunology*; D001483:Base Sequence; D002460:Cell Line; D002999:Clone Cells; D015870:Gene Expression; D005802:Genes, MHC Class II; D015803:HLA-DR3 Antigen / Q000235:genetics*; D006801:Humans; D008961:Models, Structural; D008969:Molecular Sequence Data; D009154:Mutation; D015345:Oligonucleotide Probes; D011487:Protein Conformation; D013601:T-Lymphocytes / Q000276:immunology
D015803:HLA-DR3 Antigen; D015345:Oligonucleotide Probes