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Characterization of extracellular nucleotide-induced Mac-1 (alphaM beta2 integrin) surface expression on peripheral
G K Akbar1, D C Mills, S P Kunapuli
1Department of Physiology, Temple University Medical School, Philadelphia, Pennsylvania 19140, USA.
Abstract:
Extracellular nucleotides, released during vascular injury, stimulate hematopoietic cells resulting in various physiological responses. We have determined that nucleotides can stimulate the expression of Mac-1 on peripheral blood leukocytes. ATP stimulated the expression of Mac-1 in a time- and dose-dependent manner with maximum expression occurring in 5 min at 10 microM ATP. This increase in surface expression was observed in monocytes and granulocytes was dose-dependent and was comparable in extent to the increase induced by the chemotactic peptide, formyl-Met-Leu-Phe. Other nucleotides including 2-MeSADP, ADP, UTP, and 2MeSATP had similar effect. Nucleotide-mediated stimulation of Mac-1 expression in granulocytes was completely inhibited by Ro-31-8220, a specific inhibitor of protein kinase C, while variable inhibition was observed in monocytes. These results demonstrate the stimulation of peripheral blood leukocytes by nucleotides causing an increased surface expression of Mac-1 which may be mediated by the activation of protein kinase C.
Insights
Extracellular nucleotides stimulate white blood cells to increase Mac-1 expression, a key immune cell marker. This process may involve protein kinase C activation, impacting immune responses.
Area of Science:
- Immunology
- Cell Biology
- Vascular Biology
Background:
- Extracellular nucleotides are released during vascular injury.
- These nucleotides can stimulate hematopoietic cells, leading to physiological responses.
- Mac-1 (CD11b/CD18) is an important adhesion molecule on leukocytes.
Purpose of the Study:
- To investigate the effect of extracellular nucleotides on Mac-1 expression in peripheral blood leukocytes.
- To determine the specific nucleotides involved and the kinetics of Mac-1 expression.
- To explore the signaling pathways, such as protein kinase C, mediating this effect.
Main Methods:
- Incubation of peripheral blood leukocytes with various nucleotides (ATP, ADP, UTP, etc.).
- Flow cytometry analysis to quantify surface Mac-1 expression on monocytes and granulocytes.
- Dose- and time-course experiments to determine optimal stimulation conditions.
- Inhibition studies using Ro-31-8220, a protein kinase C inhibitor.
Main Results:
- Nucleotides, particularly ATP, significantly increased Mac-1 surface expression on leukocytes in a time- and dose-dependent manner.
- Maximum Mac-1 expression was observed at 5 minutes with 10 microM ATP.
- This effect was comparable to stimulation by formyl-Met-Leu-Phe and occurred on both monocytes and granulocytes.
- Nucleotide-induced Mac-1 expression in granulocytes was fully inhibited by Ro-31-8220, suggesting protein kinase C involvement.
Conclusions:
- Extracellular nucleotides stimulate Mac-1 expression on peripheral blood leukocytes.
- This stimulation is mediated, at least in part, by the activation of protein kinase C.
- These findings highlight a novel role for nucleotides in regulating leukocyte function and immune responses.