Serotype-specific anti-pneumococcal IgG and immune competence: critical differences in interpretation criteria when different methods are used.

BACKGROUND: Serotype-specific antibody responses to pneumococcal polysaccharide are important in evaluating humoral immune function. Multiplex technologies allow simultaneous quantitation of multiple serotype-specific antibodies however there has been limited validation against the gold-standard ELISA and assay performance in the clinical setting has not been examined. METHODS AND MATERIALS: Pre- and post-immunization samples were analysed by both methods. The ability to correctly identify an adequate response to polysaccharide vaccine (as defined by current AAAAI guidelines) was determined.
RESULTS: The xMAP Pneumo 14 multiplex assay correlated poorly with the ELISA, particularly for pre-immunization and infant samples. An adequate response to pneumococcal immunization was 'correctly' predicted by xMAP Pneumo for 21 of 26 (81 %) adult pairs and 18 of 25 (72 %) infant pairs. Seven of 25 infants and 4 of 26 adults were identified as having an inadequate response by ELISA and an adequate response by xMAP.
CONCLUSION: When applying current AAAAI guidelines, the xMAP Pneumo 14 assay does not allow reliable evaluation of antibody responses to polysaccharide antigens for the assessment of humoral immune competence. New guidelines for an adequate response should be established for new technologies when evaluating responses to polysaccharide vaccine in the clinical setting.