[19] Use of liposomes as agglutination-enhancement agents in diagnostic tests

This chapter describes various methods for preparing ligand-bearing liposomes and the strategy one has followed in designing improved particle agglutination assay systems for the detection of rheumatoid factor, antinuclear antibodies, antistreptoeoecal antibodies, and anti-human erythrocyte subgroup antibodies. This chapter introduce the principle of using liposomes bearing a “second” ligand that also recognizes the analytes to amplify these specific micro-agglutination patterns. The liposomes provide the opportunity for a second binding event, in which analytes molecules, bound to the indicator particle by the primary (particle-bound) ligand, serve as receptors for the second ligand attached to the liposomes. This chapter discusses this “sandwiching effect” produces visible, specific agglutination at analytes concentrations that would normally go undetected. Specificity of the agglutination improvement provided by liposome ligand conjugates is a critical issue. In the systems described above, specificity has been confirmed by examination of large numbers of clinical specimens. This type of clinical validation is required to ensure that the improvement seen with liposomes is specific. Ligand carriers other than liposomes, (such as latex spheres of the same size as liposomes and Staphylococcus aureus) have been examined for agglutination-enhancement activity, but these have failed to provide an improvement comparable to the liposomes.