Comparative study of biological activities and mitogenic effect of extracts from Haemophilus influenzae type a

Two preparations designated as PWE and NCE were obtained from H, influenzae type a by treatment with either phenol water or hypertonic NaCl citrate respectively. The protein content of NCE was three fold higher than for PWE. Electroimmunodiffusion against H. influenzae antiserum disclosed an immunological relationship between NCE and PWE. The toxicity for mice was lower for both antigenic extracts (LD50 PWE: 47 +/- 7 mg/kg; LD50 NCE: 943 +/- 5 mg/kg) than for E. coli LPS. Limulus assay showed that both H. influenzae extracts had a weaker potency (100 to 1000 times less) than E. coli LPS. Sanarelli and Shwartzman reactions failed for PWE and NCE. The blast transformation of DBA/2 and nude mouse spleen cells were strikingly different for the three preparations: PWE, NCE, and E. coli LPS. Neither extract from H. influenzae cells showed the biological properties of a classical endotoxin. We suggest that they are endotoxin-like substances.