Development of serum antibodies of the immunoglobulin G class and subclasses against the capsular polysaccharide of Haemophilus influenzae type b in children and adults with invasive infections.

The development of total immunoglobulin G (IgG) antibodies and antibodies of the four IgG subclasses in serum against Haemophilus influenzae type b capsular polysaccharide (CPS) was studied in 24 children and 11 adults with invasive Haemophilus influenzae type b infections, by using an enzyme-linked immunosorbent assay. None of the 8 children aged 10 months or younger had increases in the IgG class or in any of the IgG subclasses. In contrast, 14 of 16 children between 10 months and 6 years of age and 10 of 11 adults had significant increases in total IgG, IgG1, or IgG2 antibodies in various combinations, but none of them had increases in IgG3 or IgG4 antibodies. The increases in IgG1 and IgG2 antibodies in the children were of similar magnitudes. Of 11 adult patients, 9 had significant increases in IgG2 antibodies, while only 4 had increases in IgG1 antibodies. In conclusion, this study shows that children younger than approximately 1 year have no IgG response to H. influenzae type b CPS, while individuals above this age have a mixed IgG1 and IgG2 response.