Fluoro-immuno-cytoadherence (FICA): A new method for the identification and enumeration of antigen-binding cells.

Antigen-coated particles of cross-linked dextran may be used for affinity chromatography of antibodies and for the fractionation of lymphoid cells with appropriate surface receptors. Furthermore, such particles serve as convenient substrates for quantitative immunofluorescence tests. The fluoro-immuno-cyto-adherence (FICA) is a simple technique which combines affinity chromatography and immunofluorescence, provides durable antigen-coated substrates and allows the identification, enumeration and characterization of lymphoid cells capable of binding an antigen, covalently linked via a spacer onto the surface of dextran beads. In the present study chicken thyroglobulin (TG) or bovine serum albumin (BSA) were coupled onto fluorescein and rhodamin-labelled or unlabelled Sephadex G-25 beads by means of spacer molecules. The specificity and degree of antigen-coating were controlled by indirect immunoflourescence. For the study of antigen-binding cells the different antigen-coated beads were mixed with suspensions of peripheral blood lymphoid cells from Obese strain (OS) chickens with spontaneous hereditary autoimmune thyroiditis, or with cells from BSA-immunized or unimmunized normal White Leghron chickens. Specific adherence of OS lymphocytes to TG-coated beads and of lymphocytes from BSA-immunized chickens to BSA-beads was found. The test and control preparations are observed simultaneously under the fluorescence microscope where the distinction of beads coated with different antigens can be made on the basis of the color of their fluorescence. Results obtained with the FICA technique are in good agreement with those of conventional rosette tests.