Platelet-activating-factor-induced augmentation of production of eosinophil-lineage cells in hematopoietic precursor cells obtained from human umbilical cord blood

Platelet-activating factor and normal or leukaemic haematopoiesis

Platelet-activating factor (PAF), a phospholipid mediator with a wide range of actions on mature leukocytes, acts directly during early human haematopoiesis by affecting the growth of haematopoietic progenitors and indirectly, by modulating cytokine synthesis by bone marrow stromal cells. At this time, its role during leukaemic diseases remains speculative. The lack of membrane PAF receptor (PAF-R) on leukaemic blasts suggest that this receptor represents a marker of mature cells and its membrane induction a consequence of cell maturation. While the couple PAF/PAF-R has been largely studied using B cell lines, few results are available using B cells of patients with haematopoietic malignancies casting some doubts concerning the potential role (if any) of this molecule during leukaemic diseases.

Effects of PAF on histamine H1 receptor mRNA expression in rat trigeminal ganglia

The application of platelet-activating factor (PAF) to the nasal mucosa of humans has been shown to increase histamine-induced hyper-reactivity. To test the hypothesis that PAF acts by increasing the reactivity of sensory nerve endings in the nasal mucosa to histamine, we examined PAF-stimulated rat trigeminal nerve ganglion cells. We found that relatively low concentrations of PAF (10(-12)-10(-9) M) induced increased histamine H1 receptor mRNA expression. This increase appeared as early as 1 h after PAF stimulation, peaked at 4 h, and disappeared after 24 h. The PAF receptor antagonist WEB2086 inhibited the increased expression of histamine H1 receptor mRNA induced by PAF, suggesting that the effects of PAF are mediated by specific receptors. This PAF effect was abolished by actinomycin D, suggesting that PAF induces de novo transcription of histamine H1 and/or PAF receptor mRNA. PAF may be important in the hyper-responsiveness of nasal mucosa exposed to histamine.

Inhibition by the anti-mitotic drug doxorubicin of platelet-activating-factor-induced late eosinophil accumulation in rats

Platelet-activating factor (PAF) has been shown, in the rat model of pleural inflammation, to induce the generation of an intermediate proteic factor able to cause eosinophil proliferation in vitro. This study was undertaken to investigate the effect of the anti-mitotic compound doxorubicin on PAF-induced eosinophilia in rats, in order to evaluate the contribution of local cell proliferation to this phenomenon. The late eosinophil infiltration caused by another chemoattractant leukotriene B4 was used for comparison. We observed that local treatment with doxorubicin (20 and 40 microg/cavity), given 6 h after PAF (1 microg/cavity), suppressed the eosinophil accumulation within 24 h, whilst only the higher dose was effective when the drug was given 12 h post-PAF. An effect on chemotaxis was ruled out, since local doxorubicin (40 microg/cavity) failed to modify the eosinophil migration noted 24 h after leukotriene B4 (0.5 microg/cavity) and the neutrophil/eosinophil infiltration noted at 6 h after PAF injection. Transfer of the pleural fluids collected 6 h after PAF from donors to recipient rats caused significant eosinophil accumulation in the recipient rats, an effect which was inhibited by the co-administration of doxorubicin (40 microg/cavity). No inhibitory effect was noted when the drug was given 6 h after the pleural fluids were transferred. We also found no change in the number of blood or bone marrow eosinophils after PAF stimulation. We conclude that doxorubicin selectively impaired the late eosinophil accumulation triggered by PAF in the pleural cavity of rats, clearly indicating that local cell proliferation seems to contribute to the development of this inflammatory response.

PAF and haematopoiesis: III. Presence and metabolism of platelet-activating factor in human bone marrow

Platelet-activating factor (PAF) is a phospholipid compound with major immunoregulatory activities. The present study shows that human bone marrow contains 576 +/- 39 pg PAF/ml (n = 35). Bone marrow-derived PAF exhibits the same biophysical and biological properties that synthetic PAF. PAF concentrations in bone marrow are correlated with the granulocyte (r = 0.4, P = 0.02) but not with the lymphocyte (r = 0.24, P = 0.17) and the monocyte (r = 0.12, P = 0.48) counts. In bone marrow PAF is inactivated by a plasma PAF acetylhydrolase activity (48.0 +/- 2.3 nmol/min per ml, n = 34). Experiments with [3H]PAF indicate that human bone marrow cells actively metabolize this potent molecule by the deacetylation-transacylation pathway. Results of this investigation indicate the permanent presence of significant amounts of PAF in bone marrow suggesting its putative involvement in the processes of bone marrow cell proliferation and maturation.