Human Blood T Cells: Response to Phytohemagglutinin

Evidence has accumulated to indicate that two different populations of lymphocytes are responsible for immunologic responsiveness. The functional characteristics of these cells appear to differ; thymic-derived or T lymphocytes3 are associated with cellular immune responses whereas B lymphocytes (probably bone marrow-derived or bursa-dependent) have been implicated in humoral aspects of the immune response (1). The isolation and characterization of T and B lymphocytes are essential for a full assessment of their functions. Recently surface markers on lymphocytes have provided a tool for identifying their origin. With direct immunofluorescent technique, lymphocytes with surface immunoglobulins have been shown in animals to be bone marrow- or bursa-derived, whereas lymphocytes of thymic origins are not stained by this technique (2–4). On the basis of this distinction it has been suggested that human peripheral blood lymphocytes bearing immunoglobulins are also B cells (5). A proportion of normal human peripheral blood lymphocytes have the ability to bind spontaneously in vitro with normal sheep red blood cells (SRBC) to form rosettes (6–9). Recent studies indicate that, in humans, these rosette-forming cells (RFC) are T cells (10–15). Since preliminary studies have shown that human adult blood lymphocytes and fetal thymocytes have a greater ability to bind to SRBC in the presence of serum than in buffered saline (unpublished observations), rosette formation in the present study was always performed in serum. Based on a technique of isolation of RFC (11), this study presents a method for obtaining a highly purified T cell population from peripheral blood. It also reports a technique for rosette formation in presence of serum. Finally, we have shown that this T cell population, which has a very low thymidine incorporation in the absence of mitogen, responds to phytohemagglutinin (PHA) to a greater extent than the unseparated population.