Antigen-specific proliferative human T cell clones with specificity for diphtheria toxoid: genetic and molecular restriction by class II antigens. 
Human T lymphocyte clones (TLC) specific for diphtheria toxoid (DT) were isolated from a DR6/7 individual by cloning in soft agar in vivo sensitized T lymphocytes.  We report here the isolation and characterization of 3 of these clones by studying: (a) the kinetic of activation, (b) the surface phenotypes, (c) the fine specificity for one of the 2 DT chains and (d) the genetic restriction of the proliferative response by the haplotype DR7.  Moreover, blocking studies of the proliferative response to DT by various immunochemically characterized anti-HLA-DR monoclonal antibodies indicate that, on the DR7 molecule, more than one Ia determinant may participate in the clonal DT proliferative response.  By using human TLC of a defined specificity and well-characterized anti-DR monoclonal antibodies, such studies may help to define the functional repertoire of Ia molecules in man.