Immunopotentiation of Staphylococcus aureus type 5 capsular polysaccharide co-entrapped in liposomes with alpha-toxin

Immunopotentiation of Staphylococcus aureus type 5 capsular polysaccharide (CP5) by use of liposomes as an alternative to protein-polysaccharide conjugates was investigated. Mice were immunized twice with cationic liposomes containing CP5 alone or CP5 co-entrapped with alpha-toxin or heat-detoxified alpha-toxin. Immunogenicity of these different antigens was compared with CP5-alpha-toxin conjugates. Antibodies against CP5 were elicited in mice immunized with conjugates or liposomes containing co-entrapped CP5 and alpha-toxin. Liposomes containing CP5 alone or co-entrapped CP5 and alpha-toxoid failed to induce antibodies against CP5. All the preparations entailed an antibody response against alpha-toxin and highest antibody and neutralizing activity titers were obtained with liposomes. These results show that liposomes can be used to immunopotentiate CP5, however, a co-incorporated protein able to insert lipids bilayers is probably required.