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Induction and detection of apoptosis in human periphery blood T-cells
1Division of Tumor Immunology, Dana-Farber Cancer Institute, Boston, MA, USA.
Abstract:
Freshly isolated, human peripheral blood T (PBT) cells are resistant to induction of apoptosis. In this study, however, we have shown that although small numbers of monocytes (Mo) are required for PBT cells to proliferate optimally in response to mitogenic challenge, a relatively higher percentage of Mo results in a significant decrease in PHA-, but not ConA-induced T-cell proliferation. Interestingly, the decrease in T-cell proliferation correlated to an increase in apoptotic cell death. Moreover, ConA-induced PBT-cells underwent apoptosis in the presence of PHA-pretreated Mo, suggesting a key role of monocyte activation in this system. This apoptosis-promoting effect of activated Mo appeared to depend on contact or close proximity between Mo and PBT-cells, rather than via soluble mediators. Despite an increase in apoptosis by the presence of high numbers of Mo, PHA-stimulated PBT-cells released IL-2 at elevated levels proportional to the increasing numbers of Mo in cultures. They also expressed activation marker CD69 and the IL-2R-gamma chain on the cell surface at comparable or higher levels in the presence of high versus low numbers of Mo. These data suggest that PBT-cells can embark on a normal early phase of activation prior to undergoing apoptosis, thereby providing a model system to study how T-cells are committed to either proliferation or activation-induced apoptosis.
Insights
High monocyte (Mo) percentages decrease T-cell proliferation and increase apoptosis, despite elevated IL-2 release and activation markers. This suggests T-cells can activate before undergoing apoptosis, offering a model for studying T-cell fate.
Area of Science:
- Immunology
- Cell Biology
Background:
- Human peripheral blood T (PBT) cells are typically resistant to apoptosis.
- Monocytes (Mo) play a role in T-cell responses, but their precise impact on T-cell apoptosis is complex.
Purpose of the Study:
- To investigate the effect of varying monocyte percentages on T-cell proliferation and apoptosis.
- To explore the role of monocyte activation in T-cell apoptosis induction.
Main Methods:
- Isolated human peripheral blood T cells and monocytes were cultured together.
- T-cell proliferation was measured using PHA and ConA mitogenic challenges.
- Apoptosis, IL-2 release, and cell surface marker expression (CD69, IL-2R-gamma) were analyzed.
Main Results:
- Optimal T-cell proliferation required low monocyte numbers; higher percentages decreased PHA-induced proliferation.
- Increased monocyte percentages correlated with higher T-cell apoptosis, particularly with PHA-stimulated monocytes.
- Activated monocytes promoted apoptosis via cell contact, not soluble factors.
- Despite apoptosis, PHA-stimulated T-cells showed increased IL-2 release and activation markers with higher monocyte counts.
Conclusions:
- Monocyte activation status critically influences T-cell apoptosis.
- T-cells can initiate activation before undergoing apoptosis, providing a model to study commitment to proliferation versus apoptosis.
- Understanding this balance is crucial for immune regulation and T-cell-mediated diseases.