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Human alveolar macrophages (AMs) from allergic asthmatics (AAs) showed continuous Li + -sensitive production of IP 1 , indicating that the cells were continuously activated. Furthermore, whereas the accumulation of IP 1 , IP 2 and IP 3 rapidly increased by as much as 125—175% in chemotactic-factor-stimulated AMs from healthy subjects, stimulation of cells from AAs increased these inositol phosphates only slightly. This moderate production could be due to a permanent state of activation leading to a depleted pool of polyphosphoinositides, corroborating the greater capacity of these cells to generate superoxide anion after stimulation by a chemoattractant. The activation state could be due to the action of priming agents, which are known to be released into the inflammatory sites.

The uptake of phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylserine (PS) in Plasmodium knowlesi infected erythrocytes has been studied. Whereas uptake of phospholipids, in the absence of phospholipid transfer proteins, is negligible in control cells, the infected cells can incorporate considerable amounts of added phospholipids. The uptake is enhanced by the presence of lipid transfer proteins. Doubly labeled [3H]oleate, [14C]choline) PC does not undergo any appreciable remodelling following uptake, which strongly suggests that plasma PC is used as such for the biogenesis of the parasite membranes. Transport of extracellularly offered PS and PE towards the intraerythrocytic parasite and utilization of these lipids by the parasite are confirmed by the observation that these lipids are converted into respectively PE and PC. The extent and rate of these conversions depend on the way the phospholipids are introduced into the infected cells.

In Plasmodium falciparum-infected erythrocyte homogenates, the specific activity of ethanolamine kinase (7.6 +/- 1.4 nmol phosphoethanolamine/10(7) infected cells per h) was higher than choline kinase specific activity (1.9 +/- 0.2 nmol phosphocholine/10(7) infected cells per h). The Km of choline kinase for choline was 79 +/- 20 microM, and ethanolamine was a weak competitive inhibitor of the reaction (Ki = 92 mM). Ethanolamine kinase had a Km for ethanolamine of 188 +/- 19 microM, and choline was a competitive inhibitor of ethanolamine kinase with a very high Ki of 268 mM. Hemicholinium 3 inhibited choline kinase activity, but had no effect on ethanolamine kinase activity. In contrast, D-2-amino-1-butanol selectively inhibited ethanolamine kinase activity. Furthermore, when the two enzymes were subjected to heat inactivation, 85% of the choline kinase activity was destroyed after 5 min at 50 degrees C, whereas ethanolamine kinase activity was not altered. Our results indicate that the phosphorylation of choline and ethanolamine was catalyzed by two distinct enzymes. The presence of a de novo phosphatidylethanolamine Kennedy pathway in P. falciparum contributes to the bewildering variety of phospholipid biosynthetic pathways in this parasitic organism.