Quantitation of Haemophilus influenzae serotype b capsular polysaccharide antigen in body fluids by enzyme immunoassay.

A heterogeneous enzyme immunoassay (EIA) has been developed to quantify capsular polysaccharide antigen of Haemophilus influenzae serotype b (Hib) polyribosyl - polyribitol -phosphate (PRP) in body fluids. Anti-Hib immunoglobulin G form rabbit adsorbed to the solid phase reacts with PRP existing in free soluble form in cerebrospinal fluid, serum or urine during Hib infection. IgG-anti-Hib labelled with horseradish peroxidase then links to PRP; the enzyme activity is measured by oxidation of the chromogenic substrate o-phenylenediamine. PRP concentrations ranged between 2 micrograms/1 to 21 mg/1 detected in acute Hib disease. The applicability of the EIA as a diagnostic aid is limited by cross-reaction of other bacterial antigens. However, quantitative measurements of PRP by enzyme immunoassay should improve studies on Hib disease.