Specificity of HLA restricting elements for human nickel reactive T cell clones

In order to study the fine specificity of HLA class II restriction, we have established nickel specific T cell clones from a nickel allergic patient. Cells were cloned by limiting dilution after primary stimulation and selection of nickel specific blasts. Several clones were established which were all shown to carry the CD4 marker. All clones were shown to be completely blocked by monoclonal antibodies directed against DR antigens, but unaffected by antibodies against DQ or DP, thus demonstrating their DR specificity. For the study of HLA class II restriction, a panel of cell donors was carefully HLA typed by including the use of DRB and DQB cDNA probes. Specificity analysis, using allogeneic antigen presenting cells, revealed that the clones were either restricted to DR3- or DR4-like molecules, which is consistent with the fact that the donor was DR3, DR4 positive. However, the studies also revealed that the fine specificity of the DR3 and DR4 restriction could not be completely assessed by serological and genomic typing of panel cells. This indicates that cellularly defined HLA restriction elements recognized by T cells cannot be defined properly with available class II typing methods, and the results of these experiments documented the additional polymorphism of class II restriction elements. The clonal specificity analysis has shed further light on the biologically relevant level of DR polymorphism.