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Bacterial lipopolysaccharide enhances polymorphonuclear leukocyte function independent of changes in intracellular
J B Klein1, V Payne, T M Schepers
1Department of Medicine, University of Louisville School of Medicine, Kentucky 40292.
Abstract:
Bacterial lipopolysaccharide (LPS) enhanced expression of C3bi receptors (CR3), phagocytosis of opsonized bacteria, and subsequent hydrogen peroxide (H2O2) production by human polymorphonuclear leukocytes (PMNs). The role of changes in intracellular calcium concentration ([Ca2+]i) in LPS-induced priming was examined by determining the effect of modulators of intracellular calcium on enhanced PMN function, determining the ability of calcium ionophores to reproduce the effects of LPS, and measuring PMN [Ca2+]i following addition of LPS. Inhibition of intracellular calcium-dependent processes with TMB-8 or quin-2 blocked all three measures of LPS-induced priming. LPS did not stimulate an increase in [Ca2+]i, and calcium ionophores failed to reproduce the effect of LPS. Maintenance of [Ca2+]i is necessary for LPS priming, but an increase in [Ca2+]i is not a component of the signal transduction pathway leading to PMN priming by LPS.
Insights
Bacterial lipopolysaccharide (LPS) primes human white blood cells (PMNs) to better fight bacteria. However, LPS does not increase intracellular calcium, indicating this is not part of the signaling pathway.
Area of Science:
- Immunology
- Cellular Biology
Background:
- Bacterial lipopolysaccharide (LPS) is known to prime human polymorphonuclear leukocytes (PMNs).
- This priming enhances PMN functions such as receptor expression, phagocytosis, and reactive oxygen species production.
- The role of intracellular calcium in LPS-induced PMN priming remains unclear.
Purpose of the Study:
- To investigate the role of intracellular calcium concentration ([Ca2+]i) in LPS-induced priming of human PMNs.
- To determine if changes in [Ca2+]i mediate the enhanced functions of PMNs stimulated by LPS.
Main Methods:
- Human PMNs were treated with LPS and the effects on CR3 expression, phagocytosis, and H2O2 production were measured.
- The impact of intracellular calcium modulators (TMB-8, quin-2) on LPS-induced PMN priming was assessed.
- Calcium ionophores were used to mimic LPS effects, and intracellular calcium levels were measured in LPS-stimulated PMNs.
Main Results:
- LPS treatment significantly enhanced CR3 expression, phagocytosis of opsonized bacteria, and H2O2 production in PMNs.
- Inhibition of intracellular calcium-dependent processes using TMB-8 or quin-2 blocked all measures of LPS-induced PMN priming.
- LPS did not induce an increase in intracellular calcium concentration ([Ca2+]i) in PMNs.
- Calcium ionophores failed to reproduce the priming effects of LPS on PMN functions.
Conclusions:
- Maintenance of intracellular calcium is essential for LPS-induced PMN priming.
- However, an increase in intracellular calcium is not a required component of the signal transduction pathway mediating LPS-induced PMN priming.
- These findings suggest a complex mechanism for LPS-induced PMN activation that involves calcium but does not rely on its elevation.