The multifactorial and multistage character of protective immunity to Plasmodium falciparum, naturally acquired by an indigenous population in Burkina Faso

High Level of Specific Anti-Plasmodium Falciparum Merozoite IgG1 Antibodies in Rural Asymptomatic Individuals of Dienga, South-Eastern Gabon

Plasmodium falciparum merozoite antigens (PfMAgs) play an essential role in the development of immunity to malaria. Currently, P. falciparum: protein 113 (Pf 113), apical membrane antigen 1 (AMA1), erythrocyte binding antigens (EBA175), and reticulocyte binding protein homologue 5 (RH5) are among the most PfMAgs studied. A comparative analysis of naturally acquired antibodies against these antigens in children would increase our knowledge about the development of protective immunity. Analysis of antibodies to Pf113, PfAMA1, PfEBA175, and PfRH5 was conducted in rural population during 2013 and 2014. Both prevalence and levels of total IgG anti-PfAMA1 were higher than that of IgG anti-PfEBA175, anti-PfRH5, and anti-Pf113. Seroconversion to PfAMA1 and PfEBA175 occurred moderately in young children and reached to the maximum in adolescent and in adults. High prevalence of IgG anti-Pf113 was observed in young children of 3 to 6 years old in 2013. The four antigens were recognized by IgG 1, 2, 3, and 4 antibodies from a large proportion of the subjects, and all of them induced high levels of specific IgG1 against PfAMA1, PfEBA175, fewer by Pf113 and PfRH5. Many asymptomatic children had specific IgG1 recognizing multiple antigens, and these IgG1 antibodies could be associated with a reduced risk of developing malaria symptoms.

Malaria Elicits Type 1 Cytokines in the Human Placenta: IFN-γ and TNF-α Associated with Pregnancy Outcomes

Pregnant women, especially primigravidas, are highly susceptible to malaria infection, resulting in maternal anemia and low birth weight infants. Because circulating parasitemia is rare in the newborn, the cause of poor fetal outcomes has been unclear. We measured cytokine concentrations in placentas collected from women delivering in urban hospitals in malaria-holoendemic or nonendemic areas of Kenya. Normal placentas displayed a bias toward type 2 cytokines; type 1 cytokines IFN-γ and IL-2 were absent in placentas not exposed to malaria but present in a large proportion of placentas from a holoendemic area. TNF-α and TGF-β concentrations were significantly higher, and IL-10 concentrations significantly lower, in placentas from the holoendemic area. Among primigravidas, placental TNF-α concentrations were significantly higher in the presence of severe maternal anemia, and both IFN-γ and TNF-α were significantly elevated when a low birth weight, rather than normal weight, infant was delivered. We conclude that maternal malaria decreases IL-10 concentrations and elicits IFN-γ, IL-2, and TNF-α in the placenta, shifting the balance toward type 1 cytokines. This is the first demonstration that these placental cytokine changes are associated with poor pregnancy outcomes in humans.

A malariometric survey in a rural community in the Muheza district, Tanzania: age profiles in the development of humoral immune responses

A malariometric survey was carried out in a rural community situated in a malaria holoendemic endemic area of Tanzania. A random sample (n = 228) of different age groups was taken to elucidate the association between anti-Pf155/RESA and anti-Pf332 antibody responses and classical malaria indices. Parasitaemia, fever, splenomegaly, haematocrit and antimalarial consumption were assessed. Antibody responses against Pf155/RESA and Pf332 peptides were determined by ELISA. The age profiles of parasite density, splenomegaly, fever, haematocrit values and prevalence of antibody responses indicated intensive malaria exposure and the highest impact of malaria in small children. Forty-five percent of the study population had detectable chloroquine and desethyl-chloroquine blood levels, and the highest frequency and concentrations were recorded in the 12-23 months old. There was no significant association between the presence of drug and parasite density in the different age groups, although in the < 15 years old there was lower parasite prevalence among the children positive for drug in their blood (P < 0.05). High prevalence of antibody responses to all antigens was observed already at an early age, but the mean anti-Pf155/RESA and anti-Pf332 antibody levels increased significantly only in the adult group (P < 0.01). Significantly lower mean parasite densities were observed in high responders to Pf155/RESA and Pf332 peptides for the > or = 10 years old. For the 1-9 years, a similar difference was only observed in the high responders to Pf332. For the whole material, anti-Pf155/RESA and anti-Pf332 antibody levels correlated positively with age. When the effect of age was allowed for in analysing the relationship between parasite density and antibody level against the different antigens, a significant negative correlation was found only with regard to Pf332 in the > = 10 years age group. These results suggest that anti-Pf332 antibodies appear to be a better indicator for antiparasitic immunity, but both antigens are important for immune protection.