a particulate carrier for an agent comprising a solid core of a polysaccharide and a proteinaceous material and an organometallic polymer bonded to the core is provided . the agent has a biological activity , such as immunogenicity , and may comprise the proteinaceous material or be a separate component of the core . polysaccharide cores include dextran , starch , cellulose and derivatives thereof and the organometallic polymer includes silicones including substituted silicones . the particulate carriers are useful for delivering agents to the immune system of a subject by mucosal or parenteral administration to produce immune responses , including antibody responses .