IDENTIFICATION OF CROSS-REACTIVE T-CELL RESTRICTION EPITOPES LOCATED ON THE DR7-BETA-1 AND DR-BETA-4 MOLECULES

L cell fibroblasts transfected with HLA class II cDNA clones isolated from a cDNA library produced from a DR7 homozygous cell line were used as antigen-presenting cells (APC) for three HLA DR-restricted, diphtheria toxoid-specific T-cell clones in order to assess the antigen-presenting ability of the transfectants and to define the class II restriction of each clone. Class II-expressing transfectants are capable of presenting antigen to antigen-specific T-cell clones, although the transfectants are less efficient at antigen presentation than conventional APC. Paraformaldehyde fixation of transfectants prior to antigen pulsing abrogated antigen presentation, demonstrating that the transfectants require antigen processing. Antigen presentation by transfectants is completely inhibited by CD4-specific monoclonal antibodies (mAb) and one of four DR-specific mAb, whereas antigen presentation by conventional APC is only partially inhibited. Both the DRα:DR7β1 and DRα:DRβ4 (DRw53) molecules of the DR7 allotype serve as restriction elements for the diphtheria toxoid-specific T-cel clones. One clone is restricted by the DR7β1 molecule, another clone by the DRβ4(DRw53) molecule, and a third clone by a cross-reactive T cell epitope on DR7β1 and DRβ4(DRw53) molecules. The two DRβ4(DRw53)-restricted clones react, however, differently with a panel of HLA-DR DRw53-positive human peripheral blood lympocytes used as APC. Therefore the data presented here clearly document that the DRβ4 (DRw53) chain may serve as restriction elements for DT-specific T-cell clones. They also provide the first evidence for functional cross-reactivity of the products of two different DRβ loci and in addition emphasize the high complexity of the supertypic HLA-DRw53 specificity. © 1990.