AVIDITY OF SPECIFIC IGG ANTIBODIES ELICITED BY IMMUNIZATION AGAINST HAEMOPHILUS-INFLUENZAE TYPE-B

Aim-To investigate the avidity of specific IgG polyribosyl ribitol pho sphate (PRP) antibodies induced by three Haemophilus influenzae type b (Hib) conjugate vaccines: PRP-meningococcal outer membrane protein co mplex (PRP-OMP), PRP-non-toxic mutant diphtheria toxin, CRM(197) (HbOC ) and PRP-tetanus toroid (PRP-T). Methods-One hundred and ten infants were immunised with one of the vaccines at two, three and four months of age. Blood samples were taken after each vaccination and serum stor ed at -20 degrees C. Serum samples collected after the third course (t hat is, at five months of age) were submitted to antibody avidity asse ssment, using a urea enzyme linked immunosorbent assay (ELISA). Result s-All three conjugate vaccines elicited IgG PRP antibodies of high med ian avidity. The resultant antibody populations were heterogeneous wit h regard to avidity, which in turn was independent of PRP antibody con centration. Conclusions-With the recent findings of a correlation betw een bactericidal killing and affinity, our data highlight the need for a protective level to be expressed qualitatively as well as quantitat ively.