My research activity for the 1998 academic year involved studies aimed at explaining the immunoenhancing effect of liposome associated CTB for liposome-encapsulated antigens. Liposomes appear to be a promising oral antigen delivery system for the development of vaccines against infectious diseases, although their uptake efficiency by Peyer's patches (PP) in the gut and the subsequent induction of mucosal IgA responses remains a major concern. We have coupled the B subunit of cholera toxin (CTB) to the liposomal outer surface and shown that the effectiveness of such liposomes, containing the saliva-binding region (SBR) of Streptococcus mutans Agl/ll adhesin in generating mucosal (salivary, vaginal, and intestinal) igA as well as serum lgG responses to the parent molecule Agl/ll was significantly enhanced. This work was published in the Journal of Infection and Immunity ( 'Effectiveness of liposomes possessing surface-linked recombinant B subunit of cholera toxin as an oral antigen delivery system , Infection and Immunity 1998: 4299-4304 In an effort to investigate the mechanism of the immunoenhancement of CTB upon its conjugation to liposomes in vitro experiments have been initiated addressing targeting to GMI expressed on mucosal epithelial as well as on immune cells To visualize the uptake of liposomes by the epithelial cells of the PP we stained these particles with lipophilic fluorescent dyes. Intestinal loops containing one PP each were constructed in anesthetized mice and stained liposomes with or without CTB on their surface were injected into the ligated lumen. After one hour the PP were excised, frozen, sectioned and currently being viewed under under a fluorescent microscope. We also investigated the interaction of the liposomes with antigen presenting cells found in the M cell pocket such as macrophages and B cells. In in vitro cultures we showed that the ability of macrophages to take up liposomes is not affected by coupling CTB on their outer surface. However, targeting liposomes to the GMI receptor of purified B cells significantly enhanced the ability of B cells to endocytose and process the liposome incorporated antigen. Since B cells are more numerous than other potential antigen presenting cells in the M cell pocket this finding may indeed account for a major part of the immunoenhancing ability of the rCTB conjugated liposmes upon oral administration.