DIFFERENTIAL BIODISTRIBUTION OF ENCAPSULATED AND SURFACE-LINKED LIPOSOMAL ANTIGENS

The biodistribution of liposomal antigens either encapsulated in or su rface-linked to liposomes of similar composition was studied over time following intravenous injection and the results analyzed in relation to adjuvanticity. The two formulations were shown to behave very diffe rently in vivo. While encapsulated antigen was rapidly focused to live r and spleen as expected, surface-linked antigen exhibited a more diss eminated distribution which parallels that of the free protein, In dua l-labelling experiments, it was also shown that encapsulated antigen r emains associated with its liposomal vehicle in contrast to surface-li nked antigen which is rapidly dissociated. This dissociation was appar ently neither due to an exchange with plasma lipoproteins nor to a dir ect action of blood constituents. Besides, it was found that surface-l inked antigen was rapidly accumulated in the carcass. We propose that the retention of the surface-linked antigen in the carcass results fro m a pre-processing of the protein involving more probably mononuclear phagocytes. This pre-processing might in turn favor the dissociation o f the protein from the liposomes in a form that allows its disseminati on in the whole organism and its interaction with more efficient antig en presenting cells such as for example Langerhans or dendritic cells.