A New Cell Surface Glycoprotein Selectively Expressed on Ly 1-2 + Cytotoxic T Lymphocytes

The immune system is endowed with great flexibility. It has at its disposal a large number of alternative pathways of reaction against foreign, immunogenic substances. A sizeable part of this impressive flexibility is due to the fact that a number of subsets of specialized cell types coexist and interact within this system. Among these cell types, lymphocytes have been shown to play a dominating role in both the specific induction of the immune response and in its further developments. Within the two major groups of lymphocytes (T and B cells) there exist additional subgroups with unique functional properties. Our knowledge of T-lymphocyte subgroups stems largely from experiments using a combination of serological and functional markers to define these cells (1-4). In principle, virgin lymphocytes, although preprogrammed as to their eventual subgroup (1), normally fail to express the functional properties displayed by activated cells arising from these subgroups (5, 6). The expression of these functions associated with the activated state can be interpreted to reflect qualitative as well as quantitative differences in the surface membrane composition of the cells. Thus, the cell surface membrane characteristics of lymphocytes are decisive factors in determining the potential activity of these cells, and although progress in this field is rapid, we still have a largely imperfect understanding of how these membrane components effect and regulate immune reactivity. In this article we have focused our attention on T lymphocytes and their membrane glycoprotein composition after induction by immunogen or polyclonal T-cell activators. With the aid of fractionation procedures now available to enrich for murine T cells with a defined surface structure or function, in combination with procedures for selective labeling of cell surface glycoproteins, comparisons between virgin and immune T cells at different stages of differentiation have been made. As will be demonstrated, this approach has been a highly fruitful one, allowing the successful characterization of a new T-lymphocyte unique surface glycoprotein associated with a defined subgroup of cells and expressed in conjunction with the cytolytic stages of T-cell reactivity. The implications of these findings will be discussed.