IMMUNOADJUVANT ACTIVITY OF A LIPOSOMAL IL-6 FORMULATION

The adjuvant effect of interleukin 6 (IL-6) entrapped in liposomes was evaluated using a 65 kDa heat shock protein as a model antigen. The s econdary humoral immune response either to antigen alone, or incorpora ted into liposomes, and the effect of IL-6 entrapped in liposomes, on this response were studied in Balb/c mice. The adjuvanticity of these formulations was compared with that of potent adjuvants such as Ribi a nd dimethyldioctadecylammoniumbromide (DDA). The importance of IL-6 du ring adjuvant activity was supported by the observation that high seru m IL-6 levels were induced in Balb/c mice by all members of a panel of adjuvants tested. Following incorporation into liposomes, IL-6 retain ed its full biological activity, as shown by its capacity to sustain g rowth of the IL-6-dependent B9 cell line. At antigen dosages where Rib i and DDA gave minimal or no secondary antibody titres, incorporation of antigen into liposomes resulted in measurable secondary antibody ti tres. Interestingly, this adjuvant activity was significantly enhanced when liposomes containing IL-6 were co-injected with the liposomal an tigen formulation. These results illustrate the potential adjuvant pro perties of this formulation, which seem especially useful for vaccines containing weak or non-immunogenic antigens.