Abstract
Age- and exposure-dependent immune responses during a malaria episode may be key to understanding the role of these factors in the acquisition of immunity to malaria. Plasma/serum samples collected from naïve Mozambican children (n = 48), European adults (naïve travelers, n = 22; expatriates with few prior malaria exposures, n = 15) and Mozambican adults with long-life malaria exposure (n = 99) during and after a malaria episode were analyzed for IgG against merozoite proteins by Luminex and against infected erythrocytes by flow cytometry. Cytokines and chemokines were analyzed in plasmas/sera by suspension array technology. No differences were detected between children and adults with a primary infection, with the exception of higher IgG levels against 3D7 MSP-142 (P = 0.030) and a P. falciparum isolate (P = 0.002), as well as higher IL-12 (P = 0.020) in children compared to other groups. Compared to malaria-exposed adults, children, travelers and expatriates had higher concentrations of IFN-γ (P≤0.0090), IL-2 (P≤0.0379) and IL-8 (P≤0.0233). Children also had higher IL-12 (P = 0.0001), IL-4 (P = 0.003), IL-1β (P = 0.024) and TNF (P = 0.006) levels compared to malaria-exposed adults. Although IL-12 was elevated in children, overall the data do not support a role of age in immune responses to a first malaria episode. A TH1/pro-inflammatory response was the hallmark of non-immune subjects.
Highlights
The worldwide burden of disease from malaria remains a major public health problem, with approximately 216 million cases and 655,000 deaths in 2010, with the majority of deaths occurring in sub-Saharan Africa [1]
Children with no documented prior malaria episodes and malaria-exposed adults were from malaria endemic areas of Mozambique, whereas travelers and expatriates were from non-malaria endemic countries
Travelers had never experienced malaria before, whereas expatriates had lived in malaria endemic areas and 12 out of 15 reported at least one previous malaria episode
Summary
The worldwide burden of disease from malaria remains a major public health problem, with approximately 216 million cases and 655,000 deaths in 2010, with the majority of deaths occurring in sub-Saharan Africa [1]. There is no clear evidence for an effect of age at first exposure to Plasmodium falciparum in the development of immunity in African children [5,6], previous studies in malaria – naıve migrants in Indonesia suggested that the more mature immune system from an adult may allow acquisition of immunity more rapidly than the less mature immune system from a child under the same conditions of exposure [7,8] Naıve adults such as travelers or migrants never exposed to P. falciparum going to malaria-endemic areas are more susceptible to clinical and severe malaria than adults from endemic areas [2,9,10]. It has been suggested that naıve adults are initially more susceptible to severe disease than children [2,11] and show different clinical presentations [12]
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