Relation between enzyme-linked immunosorbent assay and radioimmunoassay for detection of antibodies to the capsular polysaccharide of Haemophilus influenzae type b

Quantitative measurements of Hemophilus influenzae type b capsular polysaccharide antibodies in Japanese children

BACKGROUND

Hemophilus influenzae type b (Hib) infection has a high morbidity and mortality rate in children. The frequency of natural immunity against Hib in Japanese children is not known, and Hib vaccine has not yet been introduced in Japan.

METHODS

Anti-capsular polysaccharide-specific IgG (anti-CP) antibody titers were examined in serum samples from 100 children and 107 young adults who were not vaccinated against Hib, in serum samples from eight patients with Hib systemic infection and in 10 commercially available human immune globulin preparations on enzyme-linked immunosorbent assay.

RESULTS

A total of 44% (44/100) of Japanese children and all patients with Hib systemic infection in the acute phase did not have the minimum protective level of anti-CP antibodies (>0.15 microg/mL). The rate of natural Hib immunity was lowest in children under 1 year of age and gradually increased with age. Only 3.74% (4/107) of Japanese young adults did not have the minimum protective level of anti-CP antibodies. Analysis of 10 commercially available human immune globulin preparations indicated an average level of 28.25 microg anti-CP antibody/mL immune globulin (range 14.96-44.17 microg/mL).

CONCLUSIONS

Approximately half of Japanese children are not protected against Hib infection. Therefore, Hib vaccine should immediately be included as part of the routine immunization program in Japan. It was also found that all tested commercially available immune globulin preparations had high anti-CP titers. Well-controlled clinical trials of i.v. immune globulin administration for prevention and treatment of Hib systemic infection are needed in Japan.

Characterization of immune response as an indicator of Haemophilus influenzae type b vaccine efficacy

Quantitation of antibodies to Haemophilus influenzae type b (Hib) polysaccharide has been an active area of investigation associated with the development of polysaccharide and subsequently polysaccharide-protein conjugate vaccines. These clinical studies indicate that there are several serologic parameters associated with Hib vaccine efficacy in infants. Efficacious vaccines elicit polysaccharide-specific antibodies in infants; they prime the immune system for an anamnestic response; the immune response is long-lived through the period of greatest risk for disease; and the elicited antibodies have functional activity as demonstrated in bactericidal and opsonophagocytic assays or protection in an infant rat challenge model. The immune response to different Hib vaccines varies both quantitatively and qualitatively. With the introduction of routine Hib vaccine immunization, vaccine performance can rely on these serologic parameters. Quantitative serologic assays, the radio-antigen binding and enzyme-linked immunosorbent assays, have been developed and standardized. The quality of the antigen as well as optimization of all assay steps and reagents are key to ensuring specific and reproducible antibody quantitation.

Characterization of the antibody response to a Haemophilus influenzae type b conjugate vaccine in children with recurrent lower respiratory tract infection

Children with recurrent lower respiratory tract infection (RLRI) may respond poorly to polysaccharide antigens. To examine how such children respond to a polysaccharide coupled to a protein carrier, we immunized 15 children with RLRI aged 8-69 months and 15 carefully age-matched healthy controls once with a Haemophilus influenzae type b (Hib) conjugate vaccine. Total IgG subclasses, total antipolysaccharide Hib antibodies, and antipolysaccharide Hib antibodies of IgM, IgG, IgA, and IgG1-4 specificity were determined by ELISA. There were no significant differences between the two groups in any single total IgG subclass, but total IgG measured as the sum of all four subclasses was significantly lower in the children with RLRI than in the controls (P = 0.036). Before vaccination, the children with RLRI had significantly less IgG antipolysaccharide Hib antibody than the controls (P = 0.005), whereas 1 month later they had significantly more IgM antibody (P = 0.038). No other significant differences were found between the groups before or after immunization with respect to antipolysaccharide Hib antibodies. Since naturally occurring IgG antibodies are thought to be acquired partly as a consequence of antigenic stimulation on mucosal surfaces, we hypothesize that the low level of specific IgG found before immunization, as well as the low total IgG in the children with RLRI, may reflect an impaired ability to prime through mucosal surfaces. This is supported by our finding of an increased IgM response to Hib conjugate vaccine in these children, since this isotype predominates in the primary immune response, i.e., in the absence of immunologic memory.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibody response to a Haemophilus influenzae type b polysaccharide tetanus toxoid conjugate vaccine in splenectomized children and adolescents

20 children and adolescents 4-18 years old and splenectomized for various reasons (spherocytosis (n = 6), idiopathic thrombocytopenia (n = 8), other (n = 6)) were immunized once with a Haemophilus influenzae type b (Hib) polysaccharide tetanus toxoid conjugate vaccine. Prior to vaccination 10/20 patients had anticapsular antibodies below what could be considered the minimum protective level in splenectomized (0.6 micrograms/ml), whereas all obtained high antibody levels after vaccination. In addition 1 infant with congenital asplenia was vaccinated at 2,4 and 6 months of age, and was shown to respond well after the second and third injection with serum antibody concentrations of 0.84 and 10.7 micrograms/ml respectively. Because asplenic individuals have an increased risk of invasive Hib infection, these data suggest that vaccination of such individuals against Hib may be justified.