Enhanced activation-induced cell death as a mechanism of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced immunotoxicity in peripheral T cells.

T cells upon activation undergo apoptosis, a process termed activation-induced cell death (AICD). In the current study, we investigated whether 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) increases AICD and whether this constitutes one of the mechanisms by which TCDD induces immunotoxicity. To this end, C57BL/6+/+, C57BL/6 gld/gld (Fas ligand-defective) and C57BL/6 lpr/lpr (Fas-deficient) mice were injected with TCDD (50 microg/kg body weight, ip) or the vehicle (corn oil) and with anti-CD3 mAbs into the footpads. 3 days later, inguinal and popliteal lymph node cells were harvested, pooled and enumerated. Cells were cultured in vitro with anti-CD3 mAbs and cell proliferation was measured. Also, such cells were studied for their ability to undergo apoptosis upon in vitro culture with either tissue culture medium alone or with anti-CD3 mAbs. The data demonstrated that lymph nodes from TCDD-treated wild-type (+/+) mice showed a decrease in cellularity and the T cells exhibited decreased responsiveness to anti-CD3 mAbs when compared to the vehicle-treated control group. Furthermore, such cells from TCDD-treated mice exhibited increased levels of apoptosis upon in vitro culture when compared to the cells from vehicle-treated mice. In contrast, activated lymph nodes from TCDD-treated C57BL/6 gld/gld and C57BL/6 lpr/lpr mice showed normal cellularity and T cell responsiveness to anti-CD3 stimulation when compared to the vehicle controls. In addition, the activated lymph node T cells from the TCDD-treated C57BL/6 gld/gld and C57BL/6 lpr/lpr mice failed to exhibit increased apoptosis when compared to the controls. The current study demonstrates that the immunotoxic effects of TCDD in activated peripheral T cells may result from increased AICD mediated through Fas-Fas ligand interactions.

Evidence for the participation of interleukin-2 (IL-2) and IL-4 in the regulation of autonomous growth and tumorigenesis of transformed cells of lymphoid origin.

In the current study, we investigated the role of interleukin-2 (IL-2) and IL-4 as autocrine growth factors responsible for autonomous growth of four murine tumor cell lines: LSA, a radiation leukemia virus-induced T-cell lymphoma; EL-4, a chemically triggered T-cell lymphoma; PE-3T, a T-cell line that underwent spontaneous transformation ex vivo; and P815, a mastocytoma. All tumor cell lines screened constitutively expressed IL-2 receptor (IL-2R) and IL-4R genes. However, only LSA and PE-3T cells expressed IL-2 and IL-4 genes constitutively, whereas EL-4 and P815 tumor cells expressed only IL-4 but not IL-2. Monoclonal antibodies (MoAbs) against IL-2, IL-4, or a combination of these, as well as MoAbs against IL-2R significantly inhibited the proliferation of LSA but not that of other tumor cell lines ex vivo. To exclude the possibility that, in other tumor cell lines, the autocrine growth factor may interact with its receptor within the cell, the ability of antisense phosphorothioate oligonucleotides to inhibit the growth of the tumor cells was tested. The antisense phosphorothioate oligonucleotides specific for IL-2, IL-4, IL-2R beta, or IL-2R gamma chains, added in culture, could markedly inhibit the growth of LSA but not that of the other tumor cell lines screened. Inasmuch as IL-2R beta and IL-2R gamma subunits also serve as a component of the receptors for IL-4, IL-7, IL-9, and IL-15, the above data suggested that such cytokine redundancy was not responsible for autonomous growth of the other tumor cell lines. Addition of exogenous IL-2 or IL-4 to the tumor cell cultures caused significant enhancement in the proliferation of PE-3T cells, whereas other cell lines were either not significantly affected or slightly inhibited from growing. Interestingly, the LSA tumor growth in nude mice was significantly inhibited after treatment of these mice with a combination of MoAbs against IL-2 and IL-4. Together, our studies show for the first time that IL-2 and IL-4 may serve as autocrine growth factors in the autonomous proliferation of tumor cells, particularly those that are retrovirally induced. Second, some tumor cell lines, despite expressing certain cytokines and their receptors constitutively, may not depend exclusively on such factors for autocrine growth.

Double-negative T cells from MRL-lpr/lpr mice mediate cytolytic activity when triggered through adhesion molecules and constitutively express perforin gene.

The lpr gene induces in mice, accumulation of large numbers of CD4-CD8- (double negative [DN]) T lymphocytes which bear adhesion molecules not characteristic of normal resting T cells. These cells fail to acquire interleukin 2 (IL-2) receptors, produce IL-2, and proliferate when activated with mitogens or monoclonal antibodies (mAbs) against the T cell receptor (TCR). Because of these poor functions in vitro, the nature and significance of DN T cells in the autoimmune disease process is not clear. In the current study, we describe a surprising finding that mAbs against CD3-TCR-alpha/beta complex can strongly trigger the lytic activity of the DN T cells to induce redirected lysis of Fc receptor-positive targets. Similar redirected lysis was also inducible using mAbs against CD44 and gp90MEL-14, molecules involved in the binding of lymphocytes to endothelial cells. The spontaneous cytotoxic potential of the DN T cells was further corroborated by demonstrating that the lpr DN T cells constitutively transcribed perforin gene but failed to express granzyme A. The current study suggests that DN T cells are capable of mediating lysis of autologous cells bearing the specific ligands for adhesion molecules involved in the signaling of cytotoxicity. These findings provide a novel insight into the functional significance of DN T cells in lpr mice and their potential role in the pathogenesis of autoimmune disease.