Effects of Malaria Products on Human Monocyte and Neutrophil Degranulation and Lysozyme Release

Plasmodium parasites are able to detoxify high amounts of heme in human red blood cells through biocrystallization into malarial pigment hemozoin (Hz), which is avidly phagocytosed by human monocytes and neutrophils. As a consequence of phagocytosis, the phenotype of these cells is dramatically altered and their functions are seriously impaired. Hz induces quite immediately an enhanced release of lysozyme, stored in the so-called gelatinase granules, and promotes complete degranulation at later time points. Hz-dependent lysozyme release has been recently investigated in a series of recent studies. Among several proinflammatory molecules, TNF-α, IL-1β, and MIP-1α/CCL3 have been indicated as potential soluble mediators of Hz-dependent lysozyme upregulation. The mechanisms of signal transduction underlying such an enhancement have also been investigated, suggesting a potential role for p38 mitogen-activated protein kinase and nuclear factor-kappaB transcriptional pathways. Finally, a major role in lysozyme release has been suggested for the lipid moiety of Hz. Interestingly, 15-HETE, a major lipoperoxidation product of Hz, was strongly supported to be the main actor in these events.