An enzyme‐linked immunosorbent assay (ELISA) for IgG and IgA antibodies to respiratory syncytial virus in low dilutions of secretions of human serum and secretions

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Abstract
An enzyme‐linked immunosorbent assay (ELISA) has been developed for titration of IgG and IgA antibodies to respiratory syncytial (RS) virus in low dilutions of human serum, colostrum, and nasopharyngeal secretions. Previously the sensitivity of RS virus ELISA on such specimens has been limited by nonspecific absorption of antibody, particularly IgA, to crude antigen preparations. For IgG antibody estimation in infant sera, this unwanted binding was reduced to workable levels by increasing the serum, salt, and detergent concentration of the diluent. Residual nonspecific binding of IgA in colostra appeared mainly due to antigen lipids or to lipoproteins. This was markedly reduced by partitioning Triton X‐100‐treated infected cell lysate antigens in Arklone. Using the modified ELISA technique for anti‐RS virus IgA, good correlations were found with unfixed cell membrane immunofluorescence (MIF) for colostra (r = 0.81, P < 0.001) and nasal secretions from adult volunteers. In several samples nonspecific absorption of antibody precluded MIF assay, but did not affect the ELISA. Although there was an overall correlation between ELISA for anti‐RS IgG antibody in sera, the complement fixation test (r = 0.75, P < 0.001), and MIF test (r = 0.82, P < 0.001), the sensitivity of ELISA for antibody responses in convalescent sera of infants from 3 months to 2 years was poor. Conversely, the sensitivity of ELISA for antibody in the sera of older children and for transplacentally acquired antibody in very young infants was higher than that for the other two tests. ELISA was thus less reliable than either CF or MIF for detecting antibody rises in paired infant sera, particularly where maternally acquired antibody remained in the acute serum. The reasons for this apparent disparity are discussed.