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 specificities to the murine Lyt-2/3 macromolecule labeled, in indirect immunofluorescent assays, a distinct lymphocyte population in the toad, Bufo 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 be associated with a single 67 kDa macromolecule in SDS-PAGE. Upon reduction, this macromolecule resolved into 38 kDa, 34 kDa and 28 kDa subunits corresponding to the alpha, alpha' and beta subunits of the murine Lyt-2/3 complex. Comparisons based on the S delta Q index of differences in amino acid compositions of HPLC-purified alpha- and alpha'-subunits of the amphibian Lyt-2/3 molecule indicated a significant structural relatedness to their murine counterpart 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.