Characterization of a human reference standard for antibody to Plasmodium falciparum merozoite surface protein 1(42)

Volunteers vaccinated with a candidate malaria vaccine containing merozoite surface protein 1(42) (MSP-1(42)) exhibit antibodies to MSP-1(42) that are measured by enzyme-linked immunosorbent assay (ELISA). The purpose of this study was to make a human reference standard for MSP-1(42) antibody measured in absolute quantity units using pooled plasma samples known to contain high titers of MSP-1(42) antibody based on previous ELISA results. Immobilized metal affinity chromatography was used to determine the amount of MSP-1(42) antibody in this plasma pool. Hexahistidine-tagged MSP-1(42) antigen adsorbed to nickel-chelating resin was used to capture MSP-1(42) antibody from the plasma pool. The intact MSP-1(42) antibody-antigen complexes were eluted and total IgG was measured by an ELISA standardized against purified human IgG. In this way, the human reference standard was determined to contain 48.3 microg/mL of MSP-1(42) antibody. This reference standard may be useful as a quantitative working standard for measuring MSP-1(42) antibody response in future vaccine clinical trials involving MSP-1.