The possibility that mucosal antibody is produced as a host response to Haemophilus influenzae type b (Hib) infection was examined in this study. 17 of 18 prospectively evaluated children ranging in age from 2 mo to 7 yr developed a detectable level of anticapsular antibody in their nasopharyngeal secretions after systemic Hib infection. The mean concentration of nasal anti-capsular antibody of the 18 children was 554 ng/mg IgA (SD = 35-8,863) during the acute phase of illness and declined to 224 ng/mg IgA (SD = 19-2,688) in convalescence. Some children had mucosal antibody detectable at least 10 mo after infection. The mucosal antibody levels were not affected by the length of illness before diagnosis, type of disease, age of the patient, sex, or presence of detectable capsular antigen or viable bacteria in the nasopharynx. The mucosal antibody was predominantly of the IgA class and occurred independent of the serum antibody. Six of the children aged less than 1 yr who did not produce and/or sustain a serum antibody level correlated with protection demonstrated a persistent mucosal antibody response. These findings suggest that the mucosal immune system may have the ability to respond at an earlier age than the serum immune system and lead us to postulate that protective secretory antibodies to prevent systemic Hib disease may be inducible in young infants in spite of the poor serum antibody response occurring at this age.
M E Pichichero, C B Hall, R A Insel