Characterization of the Serum Antibody Response to the Capsular Polysaccharide of Haemophilus influenzae Type b in Children with Invasive Infections

Abstract

The serum antibody response to the capsular polysaccharide of Haemophilus influenzae type b (Hib) was studied in 30 children aged 1 day-5 years with invasive Hib infections. From each child, serum was obtained 0-2 days, 5-11 days, 1 month, and 6-12 months after onset of symptoms. Total antibodies were determined with RIA and isotypes with ELISA. Only 2 children had antibody levels above the estimated protective level (0.15 microgram/mL) in the first serum sample. The antibody response was age dependent with wide individual variations. Children > or = 2 years had increases in IgG, IgM, and IgA antibodies with predominance of IgG. The initial IgG response was IgG1 and IgG2 with predominance of IgG1. In the last serum sample, IgG1 antibodies had decreased while IgG2 antibodies remained unchanged. Only 2 of 7 children < 1 year had a detectable antibody response. The correlation coefficient for total antibodies compared with the sum of IgG, IgM, and IgA was .88 (P < .0001) and for IgG compared with the sum of IgG1 and IgG2 was .97 (P < .0001).

Birth weight predicts response to vaccination in adults born in an urban slum in Lahore, Pakistan

“…Generally, children respond to bacterial polysaccharides with more IgG1 antibodies and adults with more IgG2 antibodies (18,19). In children 18 mo of age, there is a high proportion of nonresponders with IgG2 antibodies (20,21). The detailed background of these age differences is not really understood, but further work in this area may help to explain the lower response to the typhoid vaccine in subjects born small for gestational age.…”

Evaluation of Serum Bactericidal Antibody Assays forHaemophilus influenzaeSerotype a

“…With no vaccine against Hia, natural immunity is the only means of immune protection against the organism. Since infants produce a weak or undetectable response to polysaccharide capsule (10,19), maternal antibodies are the major source of immunity for young infants, and quantification of natural immunity in cord blood sera could be important in high-risk populations. No threshold has been established as a minimal protective level; therefore, monitoring fold increases in antibodies in acute-versus convalescent-phase sera by enzyme-linked immunosorbent assay (ELISA) to Hia polysaccharide can be used to monitor responses to infection.…”

Neisserial Immunoglobulin A1 Protease Induces Specific T-Cell Responses in Humans

“…Neonatal CD45RA cells are induced to develop an IL-4 producing a Th2 phenotype (with production of IgG1 and IgG3 antibodies), whereas adult cells develop a Th1 phenotype (production of IgG2) following stimulation with IL-12 (66). These low levels of IgG2 in young children are thought to be an important factor reflected in the age-dependent incidence of disease, since a deficiency in IgG2 causes enhanced susceptibility to encapsulated bacteria, including meningococci (4,64,68). The relatively low levels of the Th2-type cytokines observed in this study could result from the increased levels of IFN-␥, which is known to inhibit IL-10 production (13), especially since the decrease of both cytokines, IL-10 and IL-4, correlates with the increase of IFN-␥ at day 6 of culture.…”