ABSTRACT
To date, no immune correlates for blood stage-specific immunity against Plasmodium falciparum malaria parasites have been identified. Growth and/or invasion inhibition assays using sera from Phase 2a/b trials will aid in determining whether correlations with protective immunity can be established for these assays. A major constraint in the ability to evaluate functional antibody activities from populations in endemic areas is the relatively limited availability of sufficient sample quantity. For this reason, we developed a miniaturized and high-throughput method to measure growth inhibitory activity by quantification of parasite lactate dehydrogenase (pLDH) in a 384-microtiter plate format. This culture method can be extended beyond the pLDH-based readout to other techniques commonly used to determine growth/invasion inhibition.
Subject(s)
Drug Evaluation, Preclinical/methods , L-Lactate Dehydrogenase/metabolism , Malaria Vaccines/immunology , Miniaturization/instrumentation , Plasmodium falciparum/drug effects , Plasmodium falciparum/growth & development , Animals , Clinical Trials as Topic , Culture Techniques , L-Lactate Dehydrogenase/analysis , Malaria, Falciparum/blood , Malaria, Falciparum/parasitology , Miniaturization/methods , Plasmodium falciparum/enzymology , Plasmodium falciparum/immunology , Reproducibility of Results , Sensitivity and Specificity , Time FactorsABSTRACT
Antibodies are thought to be the primary immune effectors in the defense against erythrocytic stage Plasmodium falciparum. Thus, malaria vaccines directed to blood stages of infection are evaluated based on their ability to induce antibodies with anti-parasite activity. Such antibodies may have different effector functions (e.g., inhibition of invasion or inhibition of parasite growth/development) depending on the target antigen. We evaluated four methods with regards to their ability to differentiate between invasion and/or growth inhibitory activities of antibodies specific for two distinct blood stage antigens: AMA1 and MSP1(42). We conclude that antibodies induced by these vaccine candidates have different modes of action that vary not only by the antigen, but also by the strain of parasite being tested. Analysis based on parasitemia and viability was essential for defining the full range of anti-parasite activities in immune sera.
