Dual function of recombinant human CD58: inhibition of T cell adhesion and activation via the CD2 pathway

To produce large quantities of recombinant CD58 (rCD58) glycoproteins for biochemical and functional studies, a cDNA clone containing the phosphatidylinositol-linked form of human CD58 was expressed in insect cells using the baculovirus system. Gel filtration showed rCD58 to form soluble oligomeric aggregates which were functionally, antigenically, and biochemically similar to their natural counterpart. Sequence analysis of the amino- and carboxy-terminal ends of released rCD58 protein revealed that the 28 amino acid signal peptide was accurately removed. In contrast, the hydrophobic C-terminal peptide was not removed. rCD58 binds to its natural ligand CD2 with a dissociation constant Kd = 5 x 10(-8) M, which is equivalent to the affinity of physiological T cell adhesion mediated by the membrane bound CD2-CD58 receptor-ligand pair. Rosette formation of human T lymphocytes with sheep and human erythrocytes was completely abrogated. In addition, the mixed lymphocyte reaction was significantly inhibited by rCD58. Moreover, cytotoxicity of human NK clones (CD2+CD3-) was inhibited by rCD58 similar to inhibition by CD58 mAbs. In contrast, rCD58 synergized with mitogenic CD2R mAbs in T cell triggering. These data demonstrate that rCD58 might serve as a biological immunomodulator which influences T cell adhesion and activation.