Preparation and Properties of Lymphocyte Plasma Membrane

Abstract

The cell surface (plasma) membrane plays a crucial role in many diverse aspects of the cell’s behavior. Thus, the membrane acts not only as a barrier regulating the influx and efflux of ions, nutrients, and metabolites, but also provides the location for a multiplicity of molecules (“receptors”) which monitor the external environment for “messengers” such as hormones, antigens, and the surface components of other cells. The surfaces of different cell types vary with respect to the nature of their receptors and their antigenic specificities. A well-documented example of these distinctions is provided by the lymphocyte. Lymphocytes comprise essentially two populations [thymus-derived (T) and bone-marrow-derived (B) cells; Roitt et al., 1969] which can be distinguished functionally, antigenically, and in terms of their receptor activities. Thus, the surface of T lymphocytes plays major roles in cellular immunity, in immunosuppression by antilymphocytic serum, and in providing “help” in a humoral immune response, whereas the B-lymphocyte surface is primarily responsible for mediating humoral immunity (Greaves et al., 1973). Also, T cells (mouse) possess an antigenic specificity (θ)which is not shared by B cells (Raff, 1971), whereas receptors for Fc (Basten et al.,1972a,b) and the activated C3 component of complement (Nussenzweig and Pincus, 1972) are unique for B cells. Apart from these differences, the surfaces of T and B cells share histocompatibility antigens, mediate antigen recognition although not necessarily via an identical receptor, and possess receptors for plant lectins (Greaves and Janossy, 1972), polypeptide hormones [insulin (Hadden et al., 1972; Gavin et al., 1973) and growth hormone (Lesniak et al., 1973)], and small pharmacologically active molecules such as histamine (Melmon et al., 1972; Shearer et al., 1972).