BCG versus VCN: the antigenicity and the adjuvant effect of both compounds

Enzymatically active Vibrio cholerae neuraminidase (VCN) acts as an adjuvant when it is combined with an antigen. This has been demonstrated for bacterial, viral, protein, and cellular antigens and was found for the humoral, but more pronounced for the cellular immune response. In this study, the adjuvant activity of VCN for live BCG is discussed. Live BCG itself is regarded as a rather potent immunostimulator. A total of 6.5 mU of VCN, being most effective as derived from previous adjuvant experiments, was combined with 10(6) or 10(7) live BCG and injected IV into mice. Booster injections were given on day 12. Challenge was administered in the footpad on day 17 either with 6.5 mU VCN or with 5 x 10(4) or 5 x 10(6) dead BCG. Footpad swelling was recorded 24 h after challenge. After clinical examination, mice were bled and antibodies against BCG and VCN were measured. The results show that VCN specifically enhances the cellular, not the humoral, immune reaction against BCG, while BCG is unable specifically to enhance immune reaction against VCN. However, BCG unspecifically stimulates the cellular reaction of the organism against an antigen, primarily injected, subsequent to BCG for instance, against VCN.