Responses that peaked beyond the interpolation range of the standard curve are plotted in dotted lines. account when designing serological studies and vaccines based on the antigens. Background An effective malaria vaccine is MBP146-78 usually urgently needed, but to date it remains elusive. A common way of trying to establish if a given malaria parasite antigen is a good candidate for a malaria vaccine is usually by determining if an with protection against subsequent infections of malaria. However, a number of studies suggest that naturally acquired responses to malaria merozoite antigens are short-lived. Among the majority of people living in endemic areas, levels of antibodies to merozoite antigens appear to vary with the levels of malaria transmission i.e. they are highest during periods of intense transmission and lowest or undetectable at the end of periods of low transmission [1-3]. Further, levels of antibodies to merozoite antigens often tend to be higher in individuals who also have malaria parasites at the time when their antibodies are measured than in those without parasites [2,4-6]. The implication of these observations is usually important as they suggests that during serological surveys, individuals who can nonetheless mount a rapid secondary antibody response to malaria antigens upon re-infection are likely to be classified as antibody unfavorable depending on how recent their last malaria contamination was. Conversely, individuals who are positive at the survey may be unfavorable by the time they encounter the next contamination. If indeed the antibodies responses are very brief, then data MBP146-78 from longitudinal studies with long intervals between sampling days will not reflect well the dynamics of the responses. Unfortunately, estimates of the half-lives of antibody responses to malaria that can help guide the design of such studies are lacking. In this study, a closely spaced sampling schedule was used to monitor the kinetics of antibody responses to five recombinant Plasmodium falciparum merozoite antigens among Kenyan children recovering from a clinical contamination of malaria and the data used to estimate the half-life of the responses. The results of the study indicated that both IgG1 and IgG3 antibodies to merozoite antigens have very short half-lives. Methods Study population and blood sampling This IGSF8 study was carried out at Kilifi District Hospital (KDH) around the Kenyan coast. Ethical clearance for the study was given by the Kenya Medical Research Institute ethics review board. Forty eight children admitted to the pediatric ward of KDH with a primary diagnosis of malaria, but who did not fulfill the World Health Organization criteria for severe malaria [7], were recruited, if their guardian gave written consent. A venous blood sample was taken from each child at recruitment and, subsequently, at as many of the time points as possible 1, 2, MBP146-78 3, 6, 9, and 12 wks after treatment with sulphadoxine/pyrimethamine (SP). The samples were centrifuged at 700 g for 5 min to obtain plasma, which was stored at 20C. The children were examined by a clinician and a thick malaria film prepared during the follow-up visits or any other time during the study when they were unwell. Malaria treatment (SP) was given for parasitaemia in the presence of fever (axillary temperature 37.5C). Seven children from whom weeks 1 and 2 samples could not be obtained were considered lost to follow up, so the cohort for analysis comprised 41 children. ELISA IgG1 and MBP146-78 IgG3 antibody reactivity to recombinant ectodomain of P. falciparum apical merozoite antigen 1(AMA-1), the 11 kDa carboxyl portion of merozoite surface antigen 1 (MSP-119), region II of the 175 kDa erythrocytes binding antigen (EBA-175 RII), and two recombinant proteins representing the two major allelic types of MSP-2 was assessed in plasma samples from 41 children (age range = 7 C.