Antigen Expression Influencing Tissue Invasion of Hemophilus influenzae Type B

Summary

The majority of episodes of invasive Hemophilus influenzae infections are caused by capsulated, type b strains. The invasive potential of H. influenzae was investigated in an experimental rat model. Genetically similar type a and type b strains, constructed by DNA transformation, were inoculated intranasally to investigate the contribution of these capsular antigens, or linked determinants, with respect to the stages of colonization, translocation of organisms into the blood and intravascular survival. Both the type a and type b strains colonized the nasopharynx and entered the bloodstream efficiently. In contrast, the type b transformant survived significantly more efficiently than the type a transformant in the bloodstream. In addition to the differences in their capsular antigens, the transformants differed in their lipopolysaccharide composition. In separate experiments, independently obtained type b transformants which differed in their lipopolysaccharide composition, but not capsule or outer membrane proteins, were shown to be significantly different in virulence. Further studies, using cloned DNA derived from a λ gene library, provided further evidence of the independent contribution of capsular antigen and lipopolysaccharide to the pathogenicity of H. influenzae.