CHARACTERIZATION OF THE ANTIBODY-RESPONSE TO A HAEMOPHILUS-INFLUENZAETYPE-B CONJUGATE VACCINE IN CHILDREN WITH RECURRENT LOWER RESPIRATORY-TRACT INFECTION

Children with recurrent lower respiratory tract infection (RLRI) may r espond poorly to polysaccharide antigens. To examine how such children respond to a polysaccharide coupled to a protein carrier, we immunize d 15 children with RLRI aged 8-69 months and 15 carefully age-matched healthy controls once with a Haemophilus influenzae type b (Hib) conju gate vaccine. Total IgG subclasses, total antipolysaccharide Rib antib odies, and antipolysaccharide Hib antibodies of IgM, IgG, IgA, and IgG 1-4 specificity were determined by ELISA, There were no significant di fferences between the two groups in any single total IgG subclass, but total Ige measured as the sum of all four subclasses was significantl y lower in the children with RLRI than in the controls (P = 0.036). Be fore vaccination, the children with RLRI had significantly less IgG an tipolysaccharide Rib 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 Rib antibodies. Since naturally occurring IgG antibodies are thought to be aquired par tly as a consequence of antigenic stimulation on mucosal surfaces, we hypothesize that the low level of specific IgG found before immunizati on, as well as the low total Ige in the children with RLRI, may reflec t an impaired ability to prime through mucosal surfaces. This is suppo rted by our finding of an increased IgM response to Hib conjugate vacc ine in these children, since this isotype predominates in the primary immune response, i.e., in the absence of immunologic memory. In conclu sion, children with RLRI can be protected against invasive Rib infecti on as well as healthy children, but may have an immunodeficiency chara cterized by defective ability to respond to antigenic stimulation on m ucosal surfaces.