Evaluation of host humoral antibody production against Plasmodium falciparum recombinant circumsporozoite antigen in Nigerian children

Background & objectives: The challenge of malaria and efforts targeted at developing malaria vaccines triggeredthis study on the reactivity of IgG and its subclasses in the test serum specific to CSP. This work was directed atassessing the influence of age and gender on host humoral antibody against Plasmodium falciparum recombinantcircumsporozoite antigen in Nigerian children.Methods: In all, 67 serum samples (>10,000 parasites/μl of blood) collected from malaria-infected children atthe University College Hospital, Ibadan during the transmission season were analyzed by ELISA.Results: The mean absorbance values of IgG subclasses reactive against P. falciparum CSP appeared to be agedependent and ranged from 0.01 for IgG4 in younger children to 0.95 for IgG3 in older children. The sixty-sevensubjects investigated in this study had significantly higher mean IgG1 and IgG3 than the uninfected controls(p <0.01). This follows the order IgG3 >IgG1>IgG2>IgG4 which confirmed the prevalence of the cytophilicantibodies (IgG1 and IgG3) in 65% of the malaria infected children over the non-cytophilic subclasses (IgG2and IgG4). Similarly, there was low production of IgG4 and IgG2 levels in 35% of the subjects compared withcontrol. IgG was detected in the serum of North American Subjects (NAS) which served as negative control forCSP-specific IgG subclasses. Although the NAS titre was lower than that of the malaria subjects in Nigeria, itsIgG2 was, however, higher (0.16) than that of other subclasses. The mean absorbance values of total serum IgGsubclass were higher than those of IgG subclasses specific to P. falciparum circumsporozoite antigen. The meanabsorbance values of the total serum IgG subclass follows the order IgG2>IgG1>IgG4>IgG3.Interpretation & conclusion: Age and gender-dependent correlations of results suggest that acquired immunitycould play a significant role in protection from malaria. Antibody levels are higher in male than female childrenof the same age group. Antibody levels also increase with age in both the male and female children.