Standardization and validation of a cytometric bead assay to assess antibodies to multiple <it>Plasmodium falciparum</it> recombinant antigens

<p>Abstract</p> <p>Background</p> <p>Multiplex cytometric bead assay (CBA) have a number of advantages over ELISA for antibody testing, but little information is available on standardization and validation of antibody CBA to multiple <it>Plasmodium falciparum</it> antigens. The present study was set to determine optimal parameters for multiplex testing of antibodies to <it>P. falciparum</it> antigens, and to compare results of multiplex CBA to ELISA.</p> <p>Methods</p> <p>Antibodies to ten recombinant <it>P. falciparum</it> antigens were measured by CBA and ELISA in samples from 30 individuals from a malaria endemic area of Kenya and compared to known positive and negative control plasma samples. Optimal antigen amounts, monoplex <it>vs</it> multiplex testing, plasma dilution, optimal buffer, number of beads required were assessed for CBA testing, and results from CBA vs. ELISA testing were compared.</p> <p>Results</p> <p>Optimal amounts for CBA antibody testing differed according to antigen. Results for monoplex CBA testing correlated strongly with multiplex testing for all antigens (<it>r</it> = 0.88-0.99, <it>P</it> values from <0.0001 - 0.004), and antibodies to variants of the same antigen were accurately distinguished within a multiplex reaction. Plasma dilutions of 1:100 or 1:200 were optimal for all antigens for CBA testing. Plasma diluted in a buffer containing 0.05% sodium azide, 0.5% polyvinylalcohol, and 0.8% polyvinylpyrrolidone had the lowest background activity. CBA median fluorescence intensity (MFI) values with 1,000 antigen-conjugated beads/well did not differ significantly from MFI with 5,000 beads/well. CBA and ELISA results correlated well for all antigens except apical membrane antigen-1 (AMA-1). CBA testing produced a greater range of values in samples from malaria endemic areas and less background reactivity for blank samples than ELISA.</p> <p>Conclusion</p> <p>With optimization, CBA may be the preferred method of testing for antibodies to <it>P. falciparum</it> antigens, as CBA can test for antibodies to multiple recombinant antigens from a single plasma sample and produces a greater range of values in positive samples and lower background readings for blank samples than ELISA.</p