MECHANISM OF ANTIBODY-MEDIATED REDUCTION OF NASOPHARYNGEAL COLONIZATION BY HAEMOPHILUS-INFLUENZAE TYPE-B STUDIED IN AN INFANT RAT MODEL

The mechanism of antibody-mediated reduction of Haemophilus influenzae type b (Hib) carriage was studied in the infant rat colonization mode l. Monoclonal Hib polysaccharide (PS) antibody (MAb) given intranasall y or intraperitoneally and human secretory anti-Hib PS IgA given intra nasally inhibited colonization by Hib during the entire follow-up peri od (2-48 h after challenge) but did not affect colonization by Hi, a n oncapsulated variant of Hib. F(ab')(2) fragments, prepared from the MA b or from human serum anti-Hib IgG reduced Hib colonization as efficie ntly as the uncleaved molecules. Complement depletion by cobra venom t reatment had no effect on the antibody-mediated reduction of Hib colon ization. These results indicate that Fc-mediated activities of immunog lobulins are not essential in the reduction of Hib colonization. Inste ad, antibodies to Hib most likely reduce colonization by a direct effe ct on growth of the bacteria or their adherence to the nasopharyngeal mucosa.