A Rapid and Sensitive Chemiluminescence Assay for Evaluation of Functional Opsonic Activity of Haemophilus Influenzae Type B-specific Antibodies

Luminol-enhanced chemiluminescence (CL) of heterologous neutrophils was used to assess the capacity of a 1-ng/ml concentration of Haemophilus influenzae type b (Hib)-specific antibodies to induce opsonization of Hib with autologous heat-inactivated sera from children immunized with Hib capsular polysaccharide-polyribosylribitolphosphate (Hib-PRP) conjugate vaccine. Serum samples from 15 of 36 children (42%) vaccinated with Hib-PRP conjugate vaccine had protective levels of Hib-specific antibodies of > or = 1,000 ng/ml. Ten of these 15 (67%) had poor or nonfunctional opsonic activity. Of the 10 children whose sera lacked opsonic activity, 5 (50%) presented with recurrent Hib infection. In contrast, none of the sera of 20 healthy adults lacked opsonic capability. CL intensity was proportional to the concentration of anti-Hib antibodies used for opsonization. Furthermore, the titers of Hib-PRP-specific antibody in children and adults did not correlate with opsonic activity. These results suggest that luminol-enhanced CL as described here with minute concentrations of antibody for opsonization can be used to assess functional capacity of anti-Hib antibodies after vaccination or natural infection in the evaluation of patients with recurrent infections.