Fluorescence-linked immunosorbent assay (FLISA) for quantification of antibodies to food antigens

Serum antibodies of the IgG type from rabbits immunized with food antigens (beta-lactoglobulin, ovalbumin and gliadin) have been quantified using a fluorescence-linked immunosorbent assay (FLISA), with the antigens adsorbed as round spots (about 8 mm in diameter) on glass or plastic microscope slides. The indirect immunofluorescence intensities were determined using a microscope fluorometer, and compared to enzyme-linked immunosorbent assay (ELISA) in microtiter plates and diffusion-in-gel-ELISA (DIG-ELISA) in plastic petri dishes. It was found that FLISA in general became more sensitive when the antigens had been adsorbed onto a plastic (Nunclon) than onto a glass surface. When the antigens were adsorbed to the plastic slides, the relative sensitivity order (maximum serum dilution) of the assays was in general the following, ELISA greater than FLISA greater than DIG-ELISA. The fluorescence-linked method appeared to require equal or less antigen and conjugated antiserum per sample. Due to the visual inspection of the surface, inhomogeneities of the antigen-coating could be readily discovered and evaluated by several measurements within the field of antigen-antibody reaction. It is proposed that spot FLISA may be an alternative to ELISA especially when the amount of antigen or antiserum is limited.