engleski

Adjuvant action of positively charged liposomes

We have shown previously that encapsulation of model antigen ovalbumin (OVA) into negatively charged liposomes stimulated production of IgG2a antibodies and switch toward the Th1 immune response in vivo. (Habjanec et al. J. Liposome Res. 2006 ; 16:1-16) The aim of this study was to investigate positively charged liposomes, alone or with incorporated adjuvant peptidoglycan monomer, as immunoadjuvants. Inbred mice were immunized s.c. with OVA, OVA entrapped into cationic liposomes with or without PGM, prepared in several buffers of different ionic strenght, that has been shown to differently influence the entrapment efficiency (Brgles et al., manuscript submitted). So, the different buff ering conditions were used as a tool to prepare the liposomes with different content of entrapped antigen. The immune response specific for OVA was monitored by determination of total OVA-specific IgG quantity, as well as of OVA-specific IgG1 and IgG2a subtypes, the ratio of which was u! sed as an indication of the immune response direction. Antigen alone induced predominantly anti-OVA of IgG1 subtype, while OVA entrapped into positively charged liposome induced also the IgG2a subclass of OVA-specific immunoglobulins. The immune response was modulated in accordance with entrapment efficiency. Higher entrapment efficiency resulted in higher anti-OVA IgG2a production and accordingly lower IgG1/IgG2a ratio of OVA-specific antibodies. Lower entrapment efficiency resulted in lower anti-OVA IgG2a and higher IgG1/IgG2a ratio. Whatever buffering conditions used for liposome preparation, addition of PGM into liposomes always induced a switch towards the Th2 type of immune response, in comparison to the immune resp onse induced by liposomes alone.

positively charged liposomes; ionic strength; immune response direction; adjuvant; Th1/Th2 ratio

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