Effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin on anti-CD3-induced changes in T-cell subsets and cytokine production.

The influence of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure on the cytokine-dependent toxicity syndrome induced by the injection of 145-2C11 (anti-CD3), a hamster monoclonal antibody to the CD3 epsilon portion of the murine T-cell receptor, was studied. This syndrome has been attributed to the transient release of several cytokines including TNF-alpha, IFN-gamma, IL-2, IL-3, IL-6, and GM-CSF. Exposure of C57Bl/6 mice to TCDD (15 micrograms/kg) 2 days prior to anti-CD3 injection exacerbated anti-CD3-induced toxicity as evidenced by significantly enhanced and prolonged body weight loss and lymphoid tissue atrophy. Unexpectedly, TCDD exposure did not alter plasma levels of TNF or IL-2 at any time after anti-CD3 injection. However, plasma IFN-gamma was significantly reduced at 24 h and plasma IL-6 levels were elevated 48 h after anti-CD3 injection in TCDD-treated mice. In addition, TCDD exposure resulted in elevated levels of plasma GM-CSF at 24 and 48 h. Since the body weight of TCDD-treated mice diverged from vehicle-treated mice at 48 h, it suggests that the increased IL-6 and GM-CSF may have contributed to the prolonged loss of body weight. The ability of spleen cells from vehicle- and TCDD-treated mice to produce cytokines was evaluated in vitro at various times after anti-CD3 injection. TCDD treatment resulted in reduced IL-2 and GM-CSF production at 90 min but increased GM-CSF production at 48 h post-anti-CD3 injection. In contrast, TCDD exposure did not influence cytokine production by spleen cells from mice injected with a control IgG and activated in vitro with anti-CD3. Flow cytometric analysis showed that the percentage of CD4+ cells in the draining lymph nodes from TCDD-treated mice was reduced 48-144 h post-anti-CD3 injection. In contrast, the percentage of CD8+ cells was not affected by TCDD exposure. A high fraction of lymph node cells (LNC) from TCDD-treated animals showed decreased forward angle light scatter and increased 90 degrees light scatter following anti-CD3 injection, which is a pattern characteristic of cells undergoing apoptosis. In contrast, few LNC from vehicle-treated animals showed this light scatter profile. These data suggest that TCDD may be targeting T-helper cells during activation resulting in activation-driven cell death (apoptosis) rather than differentiation.