IgG subclass response to immunization with Haemophilus influenzae type b polysaccharide-outer membrane protein conjugate vaccine.

We immunized 117 children with either Haemophilus influenzae type b polysaccharide vaccine or type b polysaccharide coupled to an outer membrane protein of group B Neisseria meningitidis (conjugate vaccine), and measured the IgG, IgG1, and IgG2 subclass composition of antibody to type b polysaccharide in postimmunization sera by ELISA. The IgG responses of 51 children, 24-83 months of age, immunized for the first time with the conventional type b vaccine consisted of both IgG1 and IgG2 antibody (respective geometric means of 2.24 and 0.77 micrograms/ml). In contrast, the IgG responses of 28 infants, 2-17 months of age, immunized with conjugate vaccine were predominantly or exclusively IgG1 (genometric mean IgG1 and IgG2 antibody concentrations of 1.92 and 0.19 micrograms/ml). A total of 38 children was primed with conjugate vaccine between 2 and 17 months of age and boosted approximately 1 yr later. The 28 children boosted with type b polysaccharide vaccine showed memory antibody responses consisting of both IgG1 and IgG2 (respective geometric means of 12.7 and 4.8 micrograms/ml); the 10 children boosted with conjugate vaccine showed a similar pattern of IgG subclass responses (respective geometric means of 20.8 and 5.1 micrograms/ml, p greater than 0.4 compared to the respective geometric mean IgG1 and IgG2 values of the group boosted with polysaccharide). Thus, in children 24-83 months of age, immunization with conventional type b polysaccharide vaccine generally elicits both IgG1 and IgG2 responses, with a slight predominance of IgG1.(ABSTRACT TRUNCATED AT 250 WORDS)