Three antigenic preparations were obtained from a non-capsulated strain of Haemophilus influenzae by ultrasonic disintegration, hot phenol extraction and from a fluid culture. They were designated H. influenzae cytoplasmic antigen (H(1–5)); H. influenzae cell wall antigen (HCW); and H. influenzae culture filtrate antigen (HCF).
Studies showed that H(1–5) antigen contained heat stable and heat labile components. The heat stable fraction stained positively for polysaccharide, had a positive limulus lysate test and there was immunological cross-reactivity between this and heat stable fractions of HCW and HCF. Limulus lysate assay indicated the presence of endotoxin in HCW and HCF preparations.
Heat stable as well as heat labile antigens of H. influenzae should be given consideration in future studies regarding the pathogenicity of this organism in the lower respiratory tree. The specificity of the heat stable antigen of H. influenzae needs to be determined.