Macrophages are host cells for the pathogenic parasite Leishmania major. Neutrophils die and are ingested by macrophages in the tissues. We investigated the role of macrophage interactions with inflammatory neutrophils in control of L. major infection. Coculture of dead exudate neutrophils exacerbated parasite growth in infected macrophages from susceptible BALB, but killed intracellular L. major in resistant B6 mice. Coinjection of dead neutrophils amplified L. major replication in vivo in BALB, but prevented parasite growth in B6 mice. Neutrophil depletion reduced parasite load in infected BALB, but exacerbated infection in B6 mice. Exacerbated growth of L. major required PGE2 and TGF-β production by macrophages, while parasite killing depended on neutrophil elastase and TNF-α production. These results indicate that macrophage interactions with dead neutrophils play a previously unrecognized role in host responses to L. major infection.

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The presence of antibodies against the major stress protein, Hsp70, in patients with autoimmune diseases led us to hypothesize that Hsp70 may occur extracellularly, and could exert chaperoning and regulatory effects on various cells. We examined the action of pure Hsp/Hsc70 on the main physiological functions of human promonocytic U-937 cells. The protein was isolated from calf muscle and was shown to be a mixture of inducible Hsp70 (60%) and constitutive Hsc70 (40%) isoforms. It was observed that the addition of the protein up-regulated two major monocyte/macrophage differentiation markers, CD11c and CD23, by 20-35%, while it had no effect on CD14. The experiments performed to investigate the influence of Hsp/Hsc70 on the reaction of U-937 cells to differentiation stimuli demonstrated that the addition of the protein prior to PMA was able to inhibit binding of proper transcription factors to double-symmetry and cAMP-response elements of the c-fos early response gene promoter. Administration of exogenous Hsp/Hsc70 prior to treatment with the tumor necrosis factor-alpha significantly lowered the number of apoptotic and necrotic cells. In no case did the control protein, ovalbumin, taken in the same concentration give a comparable effect on U-937 cells. Since the Hsp/Hsc70 effects occurred within the first hour of co-incubation, and therefore they might be explained by its interaction with the cell surface, we assayed binding of the biotinylated protein to U-937 cells by immunoenzyme assay, flow cytometry and indirect immunofluorescence. Using these three techniques we were able to detect Hsp/Hsc70 bound to cells after a 20 min incubation. According to flow cytometry data, at this time 32% of cells were positively stained with streptavidin-FITC. Immunofluorescence studies demonstrated Hsp/Hsc70 bound to the cell surface after a 20 min incubation followed by induction of patch and cap-like structures. One hour later, the majority of the protein had been internalized by U-937 cells.

To investigate the possible effects of glycoinositolphospholipid (GIPL) from Trypanosoma cruzi on human antigen presenting cells, we tested their effects on lipopolysaccharide (LPS)-stimulated human macrophages and dendritic cells (DC). Human macrophages or DC were incubated with GIPL (50 g/ml) and LPS (500 pg/ml) and tumor necrosis factor alpha (TNF-␣), interleukin 8 (IL-8), IL-10, and IL-12p40 levels in supernatants were analyzed by enzyme-linked immunosorbent assay. TNF-␣, IL-10, and IL-12 secretion were significantly decreased by GIPL both in macrophages and DC. In contrast, GIPL did not alter IL-8 production. We also analyzed the expression of CD80, CD86, HLA-DR, CD40, and CD57 on the macrophage surface after stimulation with LPS in the presence or absence of T. cruzi GIPL. GIPL led to a down-regulation in the expression of all tested molecules. We additionally examined the influence of T. cruzi GIPL on the response of human DC to LPS. LPS-induced HLA-DR, CD83, and CD86 up-regulation was significantly inhibited by GIPL. A slight down-regulation in CD80 and CD40 expression on DC surfaces in the presence of GIPL was also noticed. Similarly, GIPL led to down-modulation of CD83, CD80, CD86, and HLA-DR surface expression and TNF-␣ and IL-10 production when DC were stimulated by CD40L. The ceramide portion of GIPL was responsible for most of the activity exhibited by the whole molecule. Considering the important role of the immune response in determining the fate of the host-parasite relationship, the immunoregulatory activities of T. cruzi GIPL are potentially important for parasite evasion and then pathogenesis of infection with protozoan parasites.

Chagas disease is caused by Trypanosoma cruzi and affects 18 million people in Central and South America. Here we analyzed the exposure of phosphatidylserine by the different forms of the parasite life cycle. Only the infective trypomastigotes, but not the epimastigotes or intracellular amastigotes, expose this phospholipid. This triggers a transforming growth factor beta signaling pathway, based on phosphorylated Smad 2 nuclear translocation, leading to iNOS disappearance in infected macrophages. This macrophage deactivation favors the survival of this intracellular parasite. Thus, phosphatidylserine exposure may be used by T. cruzi to evade innate immunity and be a common feature of obligate intracellular parasites that have to deal with activated macrophages.