Osteopontin and malaria: no direct effect on parasite growth, but correlation with P. falciparum-specific B cells and BAFF in a malaria endemic area

Abstract

Background The dysregulation of B cell activation is prevalent during naturally acquired immunity against malaria. Osteopontin (OPN), a protein produced by various cells including B cells, is a phosphorylated glycoprotein that participates in immune regulation and has been suggested to be involved in the immune response against malaria. Here we studied the longitudinal concentrations of OPN in infants and their mothers living in Uganda, and how OPN concentrations correlated with B cell subsets specific for P. falciparum and B cell activating factor (BAFF). We also investigated the direct effect of OPN on P. falciparum in vitro. Results The OPN concentration was higher in the infants compared to the mothers, and OPN concentration in infants decreased from birth until 9 months. OPN concentration in infants during 9 months were independent of OPN concentrations in corresponding mothers. OPN concentrations in infants were inversely correlated with total atypical memory B cells (MBCs) as well as P. falciparum-specific atypical MBCs. There was a positive correlation between OPN and BAFF concentrations in both mothers and infants. When OPN was added to P. falciparum cultured in vitro, parasitemia was unaffected regardless of OPN concentration. Conclusions The concentrations of OPN in infants were higher and independent of the OPN concentrations in corresponding mothers. In vitro, OPN does not have a direct effect on P. falciparum growth. Our correlation analysis results suggest that OPN could have a role in the B cell immune response and acquisition of natural immunity against malaria.

Acquisition of complement fixing antibodies targeting Plasmodium falciparum merozoites in infants and their mothers in Uganda

“…Specifically, we observed that complement-fixing antibodies were positively associated with schizont-specific IgG, atypical memory B cells (MBCs), and Pf+ atypical MBCs, all of which exhibit an increase in response to malaria exposure. Although previous studies have shown correlations between the acquisition of atypical MBCs, exposure to malaria, and age, the role of these cells in the formation of immune responses against malaria remains unclear ( 39 , 42 , 68 , 69 ). Moreover, our findings indicated a correlation between complement-fixing antibodies and OPN at 9 months, suggesting a potential connection between complement-fixing antibodies and the regulation of B cell differentiation through OPN-mediated pathways.…”

“…Moreover, our findings indicated a correlation between complement-fixing antibodies and OPN at 9 months, suggesting a potential connection between complement-fixing antibodies and the regulation of B cell differentiation through OPN-mediated pathways. Both OPN and BAFF might have a role in the B cell immune response against P. falciparum infection and the formation of atypical MBCs ( 39 , 47 ), but its precise function in this context is not yet fully understood. We speculate that the infant’s immune system becomes highly active in developing its own immunity against malaria around the age of 9 months.…”

“…3D7 P. falciparum was cultured at 37°C as described ( 38 , 39 ) using O+ human erythrocytes at 4% hematocrit in RPMI 1640-HEPES supplemented with 1% AlbuMAX II, 25 μg/mL gentamicin, 5 mM L-glutamine and 200 μg/mL hypoxanthine. For merozoite isolation ( 36 ), synchronization of the cultures was achieved through sorbitol treatment and early to late schizont parasites were separated from uninfected RBCs by passing through MACs magnet separation columns (Miltenyi Biotec, Germany).…”

How to Detect Antibodies Against Babesia divergens in Human Blood Samples

“…A new isolate of Babesia (Lund 1) was introduced into culture medium containing O + erythrocytes (4% hematocrit) in 25-mL flasks and cultured at 37°C in candle light boxes, as recently described [ 26 ], and similar to what has been used for P. falciparum cultures before [ 27 , 28 ]. The culture medium contained 1% Albumax II (Gibco), 5 mM L-glutamine (Gibco), 25 μg/mL gentamicin (Sigma), and 200 μg/mL hypoxanthine (Sigma) in RPMI 1640-HEPES (Gibco).…”

Babesia divergens Shows Equal Predilection for Human ABO Blood Types in an In Vitro Erythrocyte Preference Assay

“…A Babesia isolate (Lund 1) from an infected bovine (cow) blood sample in the southern part of Sweden was introduced into in vitro routine cultures of 4% hematocrit of human erythrocytes in culture medium containing RPMI 1640-HEPES (Gibco, Life Technologies Ltd., Paisley, UK) with 1% AlbuMAX II, 25 μg/mL gentamicin, 5 mM L-glutamine and 200 μg/mL hypoxanthine (all from ThermoFisher Scientific, Auckland, NZ). Parasites were cultured at 37 °C in candle light boxes as described elsewhere [ 18 , 19 ]. Aliquots of the infected bovine blood sample were introduced directly into cultures containing human erythrocytes of blood groups A, B or O.…”