STRUCTURAL CHARACTERIZATION OF AN LYT-2 3 HOMOLOG EXPRESSED ON BUFO-REGULARIS LYMPHOCYTES/

Two alloantisera and a monoclonal antibody (mAb 53-6.7) of proven spec ificities to the murine Lyt-2/3 macromolecule labeled, in indirect imm unoflourescent assays, a distinct lymphocyte population in the toad, B ufo regularis. Lyt-2/3 antigenic activities expressed by B. regularis lymphocytes have been solubilized and purified by mAb 53-6.7 affinity chromatography and found to he associated with a single 67 kDa macromo lecule in SDS-PAGE. Upon reduction, this macromolecule resolved into 3 8 kDa, 34 kDa and 28 kDa subunits corresponding to the alpha, alpha' a nd beta subunits of the murine Lyt-2/3 complex. Comparisons based on t he S Delta Q index of differences in amino acid compositions of HPLC-p urified alpha- and alpha'-subunits of the amphibian Lyt-2/3 molecule i ndicated a significant structural relatedness to their murine counterp art as well as to the human CD8 polypeptide. Our observations point to an early phylogenetic emergence of Lyt-2/3 as an important component of the T cell cytolytic apparatus during vertebrate evolution.