Efficient phagosomal maturation and degradation of Plasmodium-infected erythrocytes by dendritic cells and macrophages

Dendritic cells (DC) and macrophages phagocytose pathogens and degrade them in their phagosomes to allow for proper presentation of foreign antigens to other cells of the immune system. The Plasmodium parasite, causative agent of malaria, infects RBC that are phagocytosed by DC and macrophages during the course of infection. Under specific conditions, the functionality of these cells can be affected by phagocytosis of Plasmodium-infected RBC. We investigated whether phagosomal maturation and degradation of Plasmodium yoelii-infected RBC in phagosomes is affected in DC and macrophages. We show that recruitment of the phagolysosomal marker Lamp-1 and of MHC-II, as well as acidification of phagosomes, was achieved in a timely manner. Using P. yoelii-infected RBC labelled with a fluorescent dye or transgenic green fluorescent protein (GFP)-expressing parasites, we found a gradual, rapid decrease in the phagosome fluorescence signal, indicating that P. yoelii-infected RBC are efficiently degraded in macrophages and DC. We also observed that pre-incubation of DC with infected RBC did not affect phagosomal maturation of newly internalized P. yoelii-infected RBC. In conclusion, after phagocytosis, Plasmodium-infected RBC are degraded by DC and macrophages, suggesting that the process of phagosomal maturation is effectively completed in malaria.

Embryonic and adult stem cell-derived cardiomyocytes: lessons from in vitro models

For years, research has focused on how to treat heart failure by sustaining the overloaded remaining cardiomyocytes. Recently, the concept of cell replacement therapy as a treatment of heart diseases has opened a new area of investigation. In vitro-generated cardiomyocytes could be injected into the heart to rescue the function of a damaged myocardium. Embryonic and/or adult stem cells could provide cardiac cells for this purpose. Knowledge of fundamental cardiac differentiation mechanisms unraveled by studies on animal models has been improved using in vitro models of cardiogenesis such as mouse embryonal carcinoma cells, mouse embryonic stem cells and, recently, human embryonic stem cells. On the other hand, studies suggesting the existence of cardiac stem cells and the potential of adult stem cells from bone marrow or skeletal muscle to differentiate toward unexpected phenotypes raise hope and questions about their potential use for cardiac cell therapy. In this review, we compare the specificities of embryonic vs adult stem cell populations regarding their cardiac differentiation potential, and we give an overview of what in vitro models have taught us about cardiogenesis.