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Enhanced human monocyte cytotoxicity by platelet-activating factor
F H Valone1, R Philip, R J Debs
1Department of Medicine, VA Medical Center, San Francisco, CA 94143.
Abstract:
The capacity of platelet-activating factor (PAF) to enhance human monocyte cytotoxicity for WEHI 164 cells was examined. Spontaneous monocyte cytotoxicity was 24 +/- 2% (mean +/- SEM, n = 9). Preincubation of monocytes with 1 pM-1 nM PAF for 18 hr significantly enhanced cytotoxicity in a dose-related manner, whereas less enhancement was observed at PAF concentrations above 1 nM. Maximal PAF-induced cytotoxicity was 68 +/- 6%, which was similar to that induced by optimal concentrations of tumour necrosis factor (TNF) and interferon-gamma. The specific PAF antagonist kadsurenone inhibited PAF-induced cytotoxicity but not TNF-induced cytotoxicity. The inactive PAF analogues lysoPAF and enantioPAF did not increase monocyte cytotoxicity. Two observations suggest that TNF mediates PAF-induced cytotoxicity: specific anti-TNF antibodies inhibited PAF-induced cytotoxicity toward WEHI 164 cells, and PAF did not enhance cytotoxicity to TNF-resistant cells. PAF represents a distinct class of phospholipid monocyte activators that increase monocyte cytotoxicity by TNF-dependent mechanisms.
Insights
Platelet-activating factor (PAF) significantly boosts human monocyte cancer cell killing ability, acting through tumor necrosis factor (TNF) to enhance immune responses.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Monocytes play a crucial role in the immune system, mediating cellular cytotoxicity.
- Platelet-activating factor (PAF) is a lipid mediator with diverse biological activities.
- The precise mechanisms by which PAF influences monocyte-mediated cytotoxicity require further elucidation.
Purpose of the Study:
- To investigate the effect of Platelet-Activating Factor (PAF) on the cytotoxic activity of human monocytes against WEHI 164 tumor cells.
- To determine the role of Tumor Necrosis Factor (TNF) in PAF-mediated enhancement of monocyte cytotoxicity.
- To characterize PAF as a potential modulator of innate immune responses.
Main Methods:
- Human monocytes were preincubated with varying concentrations of PAF.
- Monocyte cytotoxicity was assessed against WEHI 164 cells.
- The effects of PAF antagonists (kadsurenone) and inactive analogues (lysoPAF, enantioPAF) were evaluated.
- The involvement of TNF was investigated using anti-TNF antibodies and TNF-resistant cells.
Main Results:
- PAF significantly enhanced monocyte cytotoxicity in a dose-dependent manner, with maximal effects observed between 1 pM and 1 nM.
- PAF-induced cytotoxicity reached levels comparable to those induced by TNF and interferon-gamma.
- PAF-induced cytotoxicity was specifically inhibited by kadsurenone and anti-TNF antibodies, but not by inactive PAF analogues.
- PAF did not enhance cytotoxicity against TNF-resistant cells, indicating TNF-dependency.
Conclusions:
- Platelet-activating factor (PAF) is a potent enhancer of human monocyte cytotoxicity against WEHI 164 cells.
- PAF-mediated enhancement of monocyte cytotoxicity is dependent on the induction of Tumor Necrosis Factor (TNF).
- PAF represents a distinct class of phospholipid activators that augment cellular immunity through TNF-dependent pathways.