Immunological methods based on antigen-coupled bacteriophages.

Abstract

Simple chemicals, many proteins, nucleic acids or polysaccharides can be coupled to bacteriophages without completely destroying their infectivity. The coupled phages are then sensitive to inactivation by the relevant antibodies. Thus it is possible to construct phage inactivation assays for antibodies or inactivation inhibition assays for antigens. The advantages of the bacteriophage methods include superior sensitivity and good stability of the reagents. The phage inactivation method detects preferably high-affinity antibodies, but what really matters is a high avidity. Because of the polyvalency IgM antibodies can have a high avidity associated with moderate affinity, and therefore low amounts of IgM class antibody, for instance natural antibody, are often measurable by this test. The chemical conjugation inactivates a proportion of the bacteriophages. If the antigen can be made chemically reactive (self-coupling), approximately 10% of the phage particles escape this inactivation and can serve as indicators of antibody action. When the antigen cannot be made chemically reactive, this inactivation is more complete and the phage assay is less satisfactory.