Allograft immunity in vitro. VI. Autonomy of T lymphocytes in target cell destruction

Expression of the acid alpha-naphthyl acetate esterase marker by activated and secondary T lymphocytes in man

Acid alpha-naphthyl acetate esterase (ANAE) activity is characteristic of resting human T lymphocytes. The expression of the ANAE marker by activated human T and B lymphocytes (blasts) and by corresponding 'secondary' lymphocytes has been investigated. Human blood lymphocytes were stimulated by selective T-cell (phytohemagglutinin (PHA) and concanavalin A (Con A)) or B-cell (Staphylococcus aureus strain Cowan 1) mitogens or in the mixed lymphocyte culture (MLC), and the percentage of blasts expressing the marker was quantiated. Whereas 95% of Con-A-activated blasts expressed the marker, approximately 25%-30% of MLC-activated blasts and only 10%-25% of PHA-activated blasts were ANAE-positive. After reversion to secondary lymphocytes, the PHA- and MLC-activated cells regained the ANAE activity, and more than 90% of the blast-derived secondary T lymphocytes were ANAE-positive. Only 2%-8% of blast cells activated by Staphylococcus aureus strain Cowan 1 were ANAE-positive. We therefore conclude that ANAE is not a reliable marker for T cells when activated cells (blasts) are considered.

Cellular immune response in vitro: I. A requirement for time-dependent T-lymphocyte cell division of cytotoxic cells in the allogeneic response

Immunocompetent lymphoid cells cultured in vitro with allogeneic stimulator cells have been shown to produce T-lymphocyte populations which are specifically cytotoxic in vitro to the stimulatory cells whether normal or malignant. Although the culture requirements as well as the allogeneic requirements are known, the events leading to the production of T-lymphocyte cytotoxic cells is poorly understood. This study examines the role of cell division in the production of allogeneic cytotoxic T-cells in vitro. The elimination of cell division during the first 24 hr of allogeneic culture does not affect the cell-mediated cytotoxic immune response in vitro. Cell division is required, however, from 24 hr through 96 hr in culture and not necessary after 96 hr.

The lethal hit stage of mouse T and non-T cell-mediated cytolysis: differences in cation requirements and characterization of an analytical "cation pulse" method

We investigated in detail the cation requirements of two different systems of mouse cell-mediated cytolysis in vitro, at their recognition, post-recognition hit and target cell disintegration stages. In T cell-mediated cytolysis, respectively Mg++ or Ca++, Ca++, and no cations, were required. In non-T cell-mediated hemolysis, respectively no cations, Mg++, and no cations, were required. Two main conclusions can be drawn. First, the cation requirements are different from one system to the other especially at the post-recognition hit stage, which strongly suggests the existence of differences between both systems as to the actual mechanism of lysis. Second, the cation requirements are different within each system from one step to another. This formed the basis of a step-by-step analysis of the lytic process, leading to the characterization of a cation pulse method for the experimental isolation and further study of the post-recognition hit stage of cell-mediated cytolysis.

Generation of cytotoxic T lymphocytes in vitro. II. Effect of repeated exposure to alloantigens on the cytotoxic activity of long-term mixed leukocyte cultures

Mouse cytotoxic T lymphocytes (CTL) were generated in unidirectional mixed leukocyte cultures (MLC) using normal C57BL/6 spleen cells as responding cells and irradiated DBA/2 spleen cells as stimulating cells. Cytotoxicity was assayed on (51)Cr-labeled P-815 (DBA/2) target cells, and the relative frequency of CTL in individual cell populations was estimated from dose-response curves. Upon inclusion of 2-mercaptoethanol in the culture medium, it was found that significant CTL activity could be detected for as long as 3 wk in primary MLC. Reexposure of MLC cells to the original stimulating alloantigens after 14-41 days in culture resulted in significant cell proliferation and rapid regeneration of high levels of immunologically specific cytotoxicity. CTL activity in these secondary cultures increased dramatically within the first 24 h and reached higher peak levels than those found at the peak of the primary response. Furthermore, proliferation and reappearance of CTL activity could be demonstrated following each of as many as four sequential alloantigenic stimulations of the same initial cell population at 20-day intervals. Interestingly, cells recovered from MLC at the peak of the primary response on day 4 were insensitive to further allogeneic stimulation. Taken together, these results are consistent with the hypothesis that CTL differentiate in MLC to become long-lived memory cells which gradually lose their cytotoxic activity. Upon reexposure to specific alloantigen, such memory CTL rapidly regain their functional activity and proliferate to generate an expanded CTL population.

Generation of cytotoxic T lymphocytes in vitro. I. Response of normal and immune mouse spleen cells in mixed leukocyte cultures

Mouse cytotoxic T lymphocytes (CTL) were generated in mixed leukocyte cultures (MLC) using spleen cells as responding cells and irradiated allogeneic spleen cells as stimulating cells. Cytotoxicity was assessed by a quantitative (51)Cr assay system and the relative frequency of CTL in individual cell populations was estimated from dose-response curves. Inclusion of 2-mercaptoethanol in the MLC medium resulted in a 20-40-fold increase in the relative number of CTL generated at the peak of the response. Under these culture conditions, cell-mediated cytotoxic activity was detectable in MLC populations as early as 48 h after the onset of the cultures. When spleen cells from mice immunized with allogeneic tumor cells 2-4 mo previously were cultured with irradiated spleen cells of the same alloantigenic specificity (MLC-Imm), it was found that the cell-mediated cytotoxic response was detectable earlier and reached higher levels than that observed in a primary MLC. At the peak of the response, MLC-Imm populations were observed to lyse up to 50% of the target cells within 3 h at a lymphocyte: target cell ratio of 0.3:1. Immunological and physical characterization of the effector cells generated in MLC-Imm indicated that they were medium to large-sized T lymphocytes. Altogether, these studies suggested the existence of an anamnestic cell-mediated cytotoxic response in MLC-Imm.