Total and functional parasite specific IgE responses in Plasmodium falciparum-infected patients exhibiting different clinical status

Abstract

Background: There is an increase of serum levels of IgE during Plasmodium falciparum infections in individuals living in endemic areas. These IgEs either protect against malaria or increase malaria pathogenesis. To get an insight into the exact role played by IgE in the outcome of P. falciparum infection, total IgE levels and functional anti-parasite IgE response were studied in children and adults, from two different endemic areas Gabon and India, exhibiting either uncomplicated malaria, severe non cerebral malaria or cerebral malaria, in comparison with control individuals.

Methodology and results: Blood samples were collected from controls and P. falciparum-infected patients before treatment on the day of hospitalization (day 0) in India and, in addition, on days 7 and 30 after treatment in Gabon. Total IgE levels were determined by ELISA and functional P. falciparum-specific IgE were estimated using a mast cell line RBL-2H3 transfected with a human Fcepsilon RI alpha-chain that triggers degranulation upon human IgE cross-linking. Mann Whitney and Kruskall Wallis tests were used to compare groups and the Spearman test was used for correlations. Total IgE levels were confirmed to increase upon infection and differ with level of transmission and age but were not directly related to the disease phenotype. All studied groups exhibited functional parasite-specific IgEs able to induce mast cell degranulation in vitro in the presence of P. falciparum antigens. Plasma IgE levels correlated with those of IL-10 in uncomplicated malaria patients from Gabon. In Indian patients, plasma IFN-gamma , TNF and IL-10 levels were significantly correlated with IgE concentrations in all groups.

Conclusion: Circulating levels of total IgE do not appear to correlate with protection or pathology, or with anti-inflammatory cytokine pattern bias during malaria. On the contrary, the P. falciparum-specific IgE response seems to contribute to the control of parasites, since functional activity was higher in asymptomatic and uncomplicated malaria patients than in severe or cerebral malaria groups.

Figure 1

Distribution of total IgE levels per clinical group in both studied populations: Gabon and India. A. Total IgE levels (μg/ml) per clinical group in Gabonese patients (non-significant Kruskall Wallis test). B. Total IgE levels (μg/ml) in Indian patients (significant Kruskall Wallis test, p = 0.0005). C. Percentage of patients with defined IgE levels per group in the Gabonese population (normal levels (N) lower than or equal to 0.500 μg/ml, moderate levels (N to 2N), from 0.501 to 1.000 μg/ml, high levels (2N to 3N), from 1,000 to 1,500 μg/ml, very high (>3N) greater than 1,500 μg/ml). D. Percentage of patients with defined levels of IgE per group in the Indian population (normal levels (N) lower than or equal to 4,000 μg/ml, moderate levels (N to 2N), from 4,000 to 8,000 μg/ml, high levels (2N to 3N), from 8,000 to 12,000 μg/ml, very high (>3N), greater than 12,000 μg/ml). Legend: EC – endemic control, AI – Asymptomatic infected, UM – uncomplicated malaria, SM – severe malaria, CM – cerebral malaria, NEC – non-endemic control, ExCM – ex-cerebral malaria.

Figure 2

A. Total IgE correlation with age in the Gabonese population (significant spearman correlation, p = 1.0 × 10-9). B. Total IgE correlation with parasitaemia in the Indian population. Significant Spearman correlation (p = 0,0001).

Figure 3

Percentage of patients with positive functional IgE against parasite antigen in the Gabonese and Indian populations. A. Distribution of patients with positive anti-parasite functional IgE, exhibiting different intensities of enzyme release per clinical group in the Gabonese population (low enzyme release, from 5 to 10%; moderate enzyme release, from 10 to 30%; and high enzyme release, greater than than 30%). B. Distribution of patients with positive anti-parasite functional IgE in the Indian population.

Figure 4

IL-10 correlation with total IgE levels in the Gabonese population. Dashed line - Asymptomatic patients (significant negative spearman correlation, p = 0.025). Bold line - Uncomplicated malaria patients (significant positive correlation, p = 0.017).

Figure 5

Cytokine correlation with IgE levels in the Indian population. A. TNF correlation with total IgE levels (significant positive spearman correlation, p = 0.0037); B. IFN-γ correlation with total IgE levels (Significant positive spearman correlation, p = 0.0028); C. IL-10 correlation with total IgE levels (significant positive spearman correlation, p = 0.0051).