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Signalling through CD28 T-cell activation pathway involves an inositol phospholipid-specific phospholipase C activity
J Nunes1, S Klasen, M D Franco
1Unité de Cancérologie et Thérapeutique Expérimentales U 119 INSERM, Marseille, France.
The Biochemical Journal
|August 1, 1993
Summary
Stimulating CD28 molecules on Jurkat T-cells with antibodies increases intracellular calcium and activates phospholipase C (PLC). This CD28 activation also triggers interleukin-2 (IL2) production, crucial for T-cell function.
Area of Science:
- Immunology
- Cell Biology
- Molecular Signaling
Background:
- The CD28 molecule is a critical co-stimulatory receptor on T-cells.
- Understanding CD28 signaling pathways is essential for T-cell activation and immune responses.
Purpose of the Study:
- To investigate the signaling events downstream of CD28 stimulation in Jurkat T-cells.
- To determine the role of phospholipase C (PLC) and intracellular calcium ([Ca2+]i) in CD28-mediated T-cell activation.
- To examine the impact of CD28 triggering on interleukin-2 (IL2) production.
Main Methods:
- Stimulation of Jurkat T-cells using a monoclonal antibody (mAb) against CD28.
- Measurement of intracellular calcium ([Ca2+]i) levels.
- Assay of polyphosphoinositide (InsPL)-specific phospholipase C (PLC) activity, including PtdInsP2 breakdown and InsP3 generation.
- Assessment of interleukin-2 (IL2) production.
- Testing the effects of various anti-CD28 mAbs and antibody cross-linking.
Main Results:
- CD28 mAb stimulation induced sustained increases in [Ca2+]i, originating from internal stores and subsequent Ca2+ influx.
- CD28 triggering activated InsPL-specific PLC, evidenced by PtdInsP2 breakdown, InsP3 and 1,2-diacylglycerol generation, and PtdIns resynthesis.
- IL2 production stimulated via CD28 was inhibited by a protein kinase C inhibitor.
- While most anti-CD28 mAbs induced PLC activity and IL2 secretion, one (CD28.5) did not unless cross-linked, which then increased [Ca2+]i.
- CD28-molecule clustering alone was sufficient to induce PLC activity.
Conclusions:
- CD28 engagement on Jurkat T-cells initiates a signaling cascade involving PLC activation and calcium mobilization.
- CD28-mediated PLC activation and subsequent calcium increase are key events leading to IL2 production.
- T-cell activation via CD28 is dependent on both receptor engagement and subsequent molecular clustering, which collectively drive downstream signaling pathways.