Antibody responses to the full-length VAR2CSA and its DBL domains in Cameroonian children and teenagers

Abstract

Background: Antigenic variation of Plasmodium falciparum erythrocyte membrane protein 1 is a key parasite mechanism for immune evasion and parasite survival. It is assumed that the number of parasites expressing the same var gene must reach high enough numbers before the host can produce detectable levels of antibodies (Ab) to the variant. VAR2CSA is a protein coded for by one of 60 var genes that is expressed on the surface of infected erythrocytes (IE) and mediates IE binding to the placenta. The idea that Ab to VAR2CSA are pregnancy-associated was challenged when VAR2CSA-specific Ab were reported in children and men. However, the frequency and conditions under which Ab to VAR2CSA are produced outside pregnancy is unclear. This study sought to determine frequency, specificity and level of Ab to VAR2CSA produced in children and whether children with hyperparasitaemia and severe malaria are more likely to produce Ab to VAR2CSA compared to healthy children.

Methods: Antibody responses to a panel of recombinant proteins consisting of multiple VAR2CSA Duffy-binding-like domains (DBL) and full-length VAR2CSA (FV2) were characterized in 193 1-15 year old children from rural Cameroonian villages and 160 children with severe malaria from the city.

Results: Low Ab levels to VAR2CSA were detected in children; however, Ab levels to FV2 in teenagers were rare. Children preferentially recognized DBL2 (56-70%) and DBL4 (50-60%), while multigravidae produced high levels of IgG to DBL3, DBL5 and FV2. Sixty-seven percent of teenage girls (n = 16/24) recognized ID1-ID2a region of VAR2CSA. Children with severe forms of malaria had significantly higher IgG to merozoite antigens (all p < 0.05), but not to VAR2CSA (all p > 0.05) when compared to the healthy children.

Conclusion: The study suggests that children, including teenage girls acquire Ab to VAR2CSA domains and FV2, but Ab levels are much lower than those needed to protect women from placental infections and repertoire of Ab responses to DBL domains is different from those in pregnant women. Interestingly, children with severe malaria did not have higher Ab levels to VAR2CSA compared to healthy children.

Keywords: Antibody; Children; Malaria; VAR2CSA.

Fig. 1

Antibody levels to merozoite antigens in neonates during the first year of life. Antibody levels to 5 merozoite antigens were measured in neonatal samples: n = 38 cord, n = 27 samples from 21 to 28 weeks neonates, and n = 24 samples from 35 to 56 week from neonates residing in Ngali/Ntouessong villages. In addition, 11 North American adults and 17 Cameroonian multigravidae were included as antibody-negative and positive experimental controls. Median and interquartile ranges (IQR) are plotted, antibody levels between two groups were compared using Mann–Whitney test. Horizontal line represents cut-off for seropositivity

Fig. 2

Antibody levels to VAR2CSA domains in neonates during the first year of life. Antibody levels to VAR2CSA DBL domains and full-length protein (FV2) were measured in neonatal samples: n = 38 cord, n = 27 samples from 21 to 28 weeks neonates and n = 24 samples from 35 to 56 week neonates residing in Ngali/Ntouessong villages In addition 11 North American adults and 17 Cameroonian multigravidae were included as antibody-negative and positive experimental controls. Median and interquartile ranges (IQR) are plotted, antibody levels between two groups were compared using Mann–Whitney test. Horizontal line represents cut-off for seropositivity

Fig. 3

Antibody levels to merozoite antigens in children from Ngali and Ntouessong rural villages. IgG levels to five merozoite antigens were measured in children 0–5 years, 6–11 years and 11–15 years residing in Ngali/Ntouessong. In addition, samples from 11 adult North Americans and 17 Cameroonian multigravidae were also measured as antibody-negative and -positive controls, respectively. Median MFI and Inter-Quartile Range (IQR) are plotted; dotted line shows cut-off for positivity. Antibody levels between 2 groups were compared using Mann–Whitney test. Horizontal line represents cut-off for seropositivity

Fig. 4

Antibody levels to VAR2CSA domains in children from Ngali II and Ntouessong rural villages. IgG levels to VAR2CSA DBL domains and full-length protein (FV2) were measured in children 0–5 years, 6–11 years and 11–15 years residing in Ngali II and Ntouessong villages. In addition, samples from 11 adult North Americans and 17 Cameroonian multigravidae were also measured as antibody-negative and -positive controls, respectively. Median MFI and Inter-Quartile Range (IQR) are plotted; dotted line shows cut-off for positivity

Fig. 5

Antibody levels to merozoite antigen in children with severe malaria. IgG levels to five merozoite antigens were measured in healthy children (HC), children with uncomplicated malaria (UM), cerebral malaria (CM), severe malaria anemia (SMA) and other severe forms of malaria (OSF). In addition, samples from 11 healthy adult North American adults and 17 Cameroonian multigravidae were also measured as antibody-negative and -positive controls, respectively. Median MFI and Inter-Quartile Range (IQR) are plotted; dotted line shows cut-off for positivity. Antibody levels between 2 groups were compared using Mann–Whitney test

Fig. 6

Antibody levels to VAR2CSA domains in children with mild and severe malaria. IgG levels to VAR2CSA DBL domains and full-length protein (FV2) were measured in healthy children (HC), children with uncomplicated malaria (UM), children with cerebral malaria (CM), severe malaria anemia (SMA) and other severe forms of malaria (OSF). In addition, samples from 11 healthy adult North Americans and 17 Cameroonian multigravidae were also measured as antibody-negative and -positive controls, respectively. Median MFI and Inter-Quartile Range (IQR) are plotted; dotted line represents cut-off for seropositivity