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Phosphoinositide hydrolysis in mitogen-stimulated human peripheral-blood T lymphocytes
1Department of Immunology, St. George's Hospital Medical School, London, U.K.
Insights
Phytohaemagglutinin and CD3 antibodies stimulate T lymphocytes, but the inositol phosphate response is slow. This suggests calcium influx contributes to the inositol trisphosphate increase in T cells.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- T lymphocytes play a crucial role in immune responses.
- Phosphoinositide hydrolysis is a key signaling pathway in cell activation.
- Inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) is a critical second messenger in calcium signaling.
Purpose of the Study:
- To investigate the characteristics of the phosphoinositide hydrolysis response in human peripheral-blood T lymphocytes stimulated by mitogens.
- To elucidate the role of calcium influx in Ins(1,4,5)P3 accumulation in T cells.
Main Methods:
- Stimulation of human peripheral-blood T lymphocytes with phytohaemagglutinin and anti-CD3 antibodies.
- Measurement of phosphoinositide hydrolysis and inositol phosphate accumulation.
- Monitoring of intracellular calcium levels using Quin-2.
- Assessment of Ins(1,4,5)P3 accumulation in response to calcium ionophore A23187.
Main Results:
- Mitogenic stimulation induced a slow and small accumulation of inositol phosphates in T lymphocytes.
- The Ins(1,4,5)P3 response was dependent on extracellular calcium.
- A slow and sustained increase in intracellular calcium was observed.
- Calcium ionophore A23187 stimulated Ins(1,4,5)P3 accumulation.
Conclusions:
- The phosphoinositide hydrolysis response in mitogen-stimulated T lymphocytes is distinct from rapid responses in other cell types.
- Receptor-mediated calcium influx appears to contribute significantly to Ins(1,4,5)P3 generation in T lymphocytes.
Abstract:
Both phytohaemagglutinin and antibodies to the CD3 molecule induced proliferation and phosphoinositide hydrolysis in human peripheral-blood T lymphocytes, but the magnitude of the inositol phosphate response was small and the rate of accumulation slow [significant increases in Ins(1,4,5)P3 were observed only after 10 min]. Hence this response differs from the well-characterized Ins(1,4,5)P3 responses of many other systems. This slow response, its abrogation in Ca2+-depleted medium, the slow and maintained increase in Ca2+ as measured by Quin-2, and the ability of the Ca2+ ionophore A23187 to stimulate Ins(1,4,5)P3 accumulation all suggest that the increase in Ins(1,4,5)P3 occurs, at least in part, as a result of receptor-mediated Ca2+ influx in mitogen-stimulated T lymphocytes.