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.

Inhibition of intramacrophage growth of Penicillium marneffei by 4-aminoquinolines.

The antimicrobial activities of chloroquine (CQ) and several 4-aminoquinoline drugs were tested against Penicillium marneffei, an opportunistic fungus that invades and grows inside macrophages and causes disseminated infection in AIDS patients. Human THP1 and mouse J774 macrophages were infected in vitro with P. marneffei conidia and treated with different doses of drugs for 24 to 48 h followed by cell lysis and the counting of P. marneffei CFU. CQ and amodiaquine exerted a dose-dependent inhibition of fungal growth, whereas quinine and artemisinin were fungistatic and not fungicidal. The antifungal activity of CQ was not due to an impairment of fungal iron acquisition in that it was not reversed by the addition of iron nitrilotriacetate, FeCl3, or iron ammonium citrate. Perl's staining indicated that CQ did not alter the ability of J774 cells to acquire iron from the medium. Most likely, CQ's antifungal activity is due to an increase in the intravacuolar pH and a disruption of pH-dependent metabolic processes. Indeed, we demonstrate that (i) bafilomycin A1 and ammonium chloride, two agents known to alkalinize intracellular vesicles by different mechanisms, were inhibitory as well and (ii) a newly synthesized 4-amino-7-chloroquinoline molecule (compound 9), lacking the terminal amino side chain of CQ that assists in drug accumulation, did not inhibit P. marneffei growth. These results suggest that CQ has a potential for use in prophylaxis of P. marneffei infections in human immunodeficiency virus-infected patients in countries where P. marneffei is endemic.

Effects of iron on extracellular and intracellular growth of Penicillium marneffei.

Killing of intracellular Penicillium marneffei conidia is demonstrated in gamma interferon-lipopolysaccharide-activated human THP1 and mouse J774 cells. Iron overload significantly reduces the antifungal activity of macrophages. Likewise, exogenous iron enhances and iron chelators inhibit the extracellular growth of P. marneffei. These results suggest that iron availability critically affects immunity to and the pathogenicity of P. marneffei.