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Correlation between antibody affinity and serum bactericidal activity in infants.
1Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, Tennessee 38101.
The Journal of Infectious Diseases
|April 1, 1992
Summary
Nearly half of infants develop low-affinity antibodies after Haemophilus influenzae type b (Hib) conjugate vaccination. Antibody affinity, not concentration, significantly correlated with protective bactericidal activity, indicating functional deficiency in some infant immune responses.
Area of Science:
- Immunology
- Pediatrics
- Vaccinology
Background:
- Infants immunized with Haemophilus influenzae type b (Hib) capsular polysaccharide (polyribosylribitol phosphate; PRP)-protein conjugate vaccines often produce low-affinity antibodies.
- The functional significance of antibody affinity in the context of Hib conjugate vaccination in infants remains unclear.
Purpose of the Study:
- To investigate the relationship between antibody affinity and biologic function, specifically bactericidal activity, in infants immunized with a Hib conjugate vaccine.
- To determine if antibody affinity is a critical factor in the protective immune response against Hib.
Main Methods:
- Sera were collected from 18-month-old infants before and one month after immunization with a PRP-diphtheria toxoid conjugate vaccine.
- Assays were performed to measure anti-PRP antibody affinity, anti-PRP and anti-outer membrane protein concentrations, immunoglobulin isotype, and serum bactericidal activity.
- Multiple regression analysis was used to correlate these parameters with bactericidal activity.
Main Results:
- Nine subjects had low-affinity anti-PRP antibodies (K < 10(4) l/mol), while 11 had higher affinity antibodies (average K = 2.8 x 10(4) l/mol).
- Multiple regression analysis revealed that antibody affinity was the only variable significantly associated with serum bactericidal activity post-vaccination (r = .71; P = .04).
- Neither antibody concentration nor immunoglobulin isotype showed a significant correlation with bactericidal activity.
Conclusions:
- A substantial proportion of infants immunized with Hib conjugate vaccine produce functionally deficient serum antibodies due to low affinity.
- Antibody affinity is a critical determinant of protective immunity elicited by Hib conjugate vaccines in infants.
- These findings highlight the importance of antibody affinity in evaluating vaccine efficacy and infant immune responses.