LIPOSOMES AND IMMUNOASSAYS

Various aspects of the application of liposomes as a label in immunoas says are reviewed. Methods for the preparation of liposomes, from the basic film method to the more advanced dehydration-rehydration method, are discussed. Furthermore, the markers used in liposome labels, as w ell as the methods to conjugate liposomes to antigens or antibodies, a re summarized. Liposome immunoassays are applied as homogeneous or het erogeneous assays. Homogeneous assays often rely on the lytic activity of complement on antibody-associated liposomes. Another group of homo geneous assays utilizes the inhibitory action of antibodies on the act ivity of conjugates of mellitin (a bee venom protein) with a hapten. F ree mellitin conjugates are able to lyse liposomes effectively. Hetero geneous liposome immunoassays, performed either competitively or non-c ompetitively, resemble more closely standard enzyme linked immunosorbe nt assays, with the enzyme being replaced by a liposome label. Washing steps are used to separate antigen-specifically bound liposomes from unbound liposomes. AII bound liposomes are lysed with a detergent, giv ing an instantaneous amplification. Flow-injection liposome immunoassa ys and liposome immunosensors are also described as examples of other possible immunoassay formats.