Chemical and biological properties of hot water extract from delipidated cells of Mycobacterium bovis strain BCG.

A water-soluble fraction was isolated from delipidated cells of Mycobacterium bovis strain BCG by extraction with hot water. Chemical analyses revealed that the above fraction presumably consisted of a peptidoglycan containing 5-10% of nucleic acids. When it was injected into guinea pigs with Freund's incomplete adjuvant plus egg white albumin as antigen, an increase of circulating antibody was observed as shown by the augmented titers of precipitin and hemagglutinin. The results of skin test and corneal reaction indicated that the fraction mentioned above induced delayed hypersensitivity to egg white albumin. Footpad reaction in mice demonstrated that the above fraction induced delayed hypersensitivity to sheep red blood cells. It was confirmed in addition that the adjuvant activity of this fraction was not due to the presence of nucleic acids. This adjuvant-active fraction was designated as HSA (hot-water soluble adjuvant.