Haemophilus influenzae type b: Disease and Immunity in Humans

Abstract

Despite an increasing frequency of Haemophilus influenzae type b meningitis in children under 5 years of age, the present age distribution is identical to that at the turn of the century, suggesting that acquisition of immunity has not changed. Immunization of adults and infants with type b capsular polysaccharide has induced formation of serum antibodies estimated to be "protective." Studies of the origin of "natural" immunity to this and other pyogenic organisms have identified enteric bacteria with cross-reacting antigens. Immunization of animals with these organisms induced serum antibodies to the capsular polysaccharides of H. influenzae type b, the meningococcus groups A and C, and pneumococcus types I and III. The heterogenous antiserums had biologic activity similar to that of the antiserum produced by the homologous organism. Haemophilus influenzae type b antibodies were induced in neonatal rabbits by the feeding of Escherichia coli having a cross-reacting antigen. These findings suggest that immunity to several pyogenic organisms may be induced by neonatal feeding of nonpathogenic enteric bacteria possessing cross-reacting antigens.