Synergistic and antagonistic interactions between haemozoin and bacterial endotoxin on human and mouse macrophages

Haemozoin (malaria pigment) is a birefringent crystalline material made of Fe (III) Protoporphyrin IX dimers that derives from the degradation of haemoglobin by intraerythrocytic Plasmodia. At schizont rupture, it accumulates indigested inside phagocytic cells altering their immunological properties. Both pro-inflammatory and immunosuppressive activities have been associated with pigment-fed monocyte-macrophages or dendritic cells. These conflicting results were attributed to the source of macrophages or the different preparations of pigment. However, the interactions of malaria pigment with other phagocytes stimuli, such as bacterial endotoxin (LPS) or interferon-gamma have not been fully analysed, yet. The purpose of this study was to compare the immunological properties of native haemozoin (HZ), freshly extracted from Plasmodium falciparum cultures, versus beta-haematin (BH), the synthetic crystals identical to native haemozoin, and to evaluate the relationship between haemozoin and endotoxin on the immune response of different macrophages populations. The results indicate that the iron-porphyrin moiety of both native and synthetic pigment can exert either a synergistic or antagonistic effect with LPS that is related to the length and sequence of treatment, the source of macrophages and is associated with the generation of oxidative stress. These data rise the question of whether and how in vivo concomitant gram(-) bacteremia may affect the pathogenesis and/or the immune response of malaria infections and vice versa.