Hemozoin differentially regulates proinflammatory cytokine production in human immunodeficiency virus-seropositive and -seronegative women with placental malaria

Abstract

Pregnant women are at an increased risk for malarial infection. Plasmodium falciparum accumulates in the placenta and is associated with dysregulated immune function and poor birth outcomes. Malarial pigment (hemozoin) also accumulates in the placenta and may modulate local immune function. In this study, the impact of hemozoin on cytokine production by intervillous blood mononuclear cells from malaria-infected placentas was investigated. There was a dose-dependent, suppressive effect of hemozoin on production of gamma interferon (IFN-gamma), with less of an effect on tumor necrosis factor alpha (TNF-alpha) and interleukin-10, in human immunodeficiency virus-seronegative (HIV(-)) women. In contrast, IFN-gamma and TNF-alpha production tended to increase in HIV-seropositive women with increasing hemozoin levels. Production patterns of cytokines, especially IFN-gamma in HIV(-) women, followed different trends as a function of parasite density and hemozoin level. The findings suggest that the influences of hemozoin accumulation and high-density parasitemia on placental cytokine production are not equivalent and may involve different mechanisms, all of which may operate differently in the context of HIV infection. Cytokine production dysregulated by accumulation of hemozoin or high-density parasitemia may induce pathology and impair protective immunity in HIV-infected and -uninfected women.

FIG. 1.

Cytokine production by IVBMC from malaria-infected placentas as a function of HIV infection status and HS. IFN-γ (A to E), TNF-α (F to J), and IL-10 (K to O) were measured in culture supernatants of IVBMC and categorized by HS (see Materials and Methods for definitions). Open circles represent HIV⁻ samples, and closed circles represent HIV⁺ samples. Medians are indicated by open diamonds joined by a dotted line (HIV⁻) and open hexagons joined by a solid line (HIV⁺). (A, F, and K) Spontaneously produced cytokine levels; (B, G, and L) PHA-stimulated cytokine levels; (C, H, and M) anti-CD3 monoclonal antibody (CD3)-stimulated cytokine levels; (D, I, and N) PPD-stimulated cytokine levels; (E, J, and O) MalAg-stimulated cytokine levels. Among HIV⁻ women, levels of spontaneously produced, CD3-stimulated, and MalAg-stimulated IFN-γ for the HS0 group were significantly higher than those for the HS1 group. The levels of spontaneously produced and PHA- and CD3-stimulated IFN-γ for the HS0 group were also significantly higher than those for the HS2 group. For IFN-γ, the response in HIV⁻ women was significantly different from that in HIV⁺ women (for PHA stimulation and those in the HS≥2 group, P = 0.029; for CD3 stimulation and those in the HS0 group, P = 0.014). *, P < 0.05; **, P < 0.02; ***, P < 0.01; ****, P < 0.001.

FIG. 2.

Cytokine production by IVBMC from malaria-infected placentas as a function of HIV infection status and placental PD. IFN-γ (A to E), TNF-α (F to J), and IL-10 (K to O) were measured in culture supernatants of IVBMC and categorized by PDs (see Materials and Methods for definitions). Symbols are as defined in the legend to Fig. 1. (A, F, and K) Spontaneously produced cytokine levels; (B, G, and L) PHA-stimulated cytokine levels; (C, H, and M) anti-CD3 monoclonal antibody (CD3)-stimulated cytokine levels; (D, I, and N) PPD-stimulated cytokine levels; (E, J, and O) MalAg-stimulated cytokine levels. Among HIV⁻ women, levels of spontaneously produced and PHA- and PPD-stimulated TNF-α in the HS1 group were significantly higher than those in the HS0 group. *, P < 0.03; **, P < 0.05; ***, P < 0.01.