Functional and biochemical characterization of immunologically derived equine platelet-activating factor

Area of Science:

• Immunology
• Biochemistry
• Platelet Physiology

Background:

• Platelet-activating factor (PAF) is a potent lipid mediator involved in various physiological and pathological processes.
• The characterization of PAF in different species, particularly in equids, is crucial for understanding its role in immune responses and hemostasis.
• Previous studies have indicated the presence of PAF-like activity in equine biological samples.

Purpose of the Study:

• To investigate the release and functional characteristics of platelet-activating factor (PAF) from equine leukocytes.
• To determine the biochemical identity of the immunologically derived equine PAF.
• To assess the responsiveness of equine and rabbit platelets to equine PAF and its effect on platelet aggregation and serotonin release.

Main Methods:

• Equine leukocytes were challenged with specific antigens to induce PAF release in vitro.
• The released equine PAF's effect on serotonin release from equine platelets was measured in a dose-dependent manner.
• Platelet aggregation assays were performed using washed equine platelets stimulated with equine PAF, with and without cyclo-oxygenase inhibitors.
• Biochemical analyses, including stability tests and chromatographic comparisons, were conducted to identify the equine PAF and compare it to 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine (AGEPC).

Main Results:

• Antigen challenge of equine leukocytes resulted in the non-lytic release of platelet-activating factor (PAF).
• Equine PAF stimulated serotonin release from equine platelets in a dose-responsive manner, independent of indomethacin.
• Equine PAF induced platelet aggregation in washed equine platelets, unaffected by aspirin or indomethacin, and desensitized platelets to further PAF stimulation.
• Biochemical properties of equine PAF were identical to AGEPC, including stability, methanolysis, and chromatographic mobility.

Conclusions:

• The immunologically derived equine platelet-activating factor (PAF) is released rapidly from leukocytes upon antigen challenge.
• Equine PAF induces serotonin release and aggregation in equine platelets through a mechanism independent of cyclo-oxygenase pathways.
• The functional and biochemical data strongly support the identity of equine PAF with 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine (AGEPC).