Abstract
We postulate that the affinity of antibody against polyribosylribitol phosphate (PRP) may be as important as concentration in host defense against Haemophilus influenzae b (Hib), and may differ for T-independent and T-dependent antigens. Using oligosaccharides (OS) from Hib we measured the intrinsic affinity (K) of antigen antibody binding rather than the relative avidity of antibody for multivalent antigen. PRP-OS were produced by acid hydrolysis and gel filtration; sized according to the number of repeating units (T/R); and radiolabelled. Affinities of purified bacterial polysaccharide hyperimmune globulin (BPIG) and of sera from vaccinated adult donors were measured by a modified Farr assay, and the total antibody binding sites (Abt) calculated. BPIG bound to OS of T/R=4, 3 and 2 with K=3.5, 2.3 and 1.5×105 M−1 respectively, while Abt was constant. Serum from ten adults vaccinated with one dose of PRP-diphtheria toxoid conjugate (PRP-D) had an average K=5.1±4.1×105M−1, compared to nine PRP vaccinated subjects with an average K=6.5±4.1×105 M−1 (p>0.1). We conclude that anti-PRP IgG binds PRP-OS with low affinity that decreases with the size of OS. Since total antibody binding sites did not vary by OS size, these data suggest that there were no subpopulations of antibody with binding restricted by OS size. Finally, the intrinsic affinity of the primary antibody response is similar regardless of vaccination with PRP or PRP-D, though further studies may show different affinities with secondary antibody responses.
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Hetherington, S. THE CALCULATION OF THE INTRINSIC AFFINITY CONSTANT K FOR ANTIBODY BINDING TO PRP OLIGOSACCHARIDES FROM HAEMOPHILUS INFLUENZAE TYPE B. Pediatr Res 21 (Suppl 4), 326 (1987). https://doi.org/10.1203/00006450-198704010-00953
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DOI: https://doi.org/10.1203/00006450-198704010-00953