Use of an ELISA-based assay for the detection of antibody-secreting cells in channel catfish, Ictalurus punctatus (Rafinesque)

Abstract. An ELISA-bascd plaque assay for the detection and quantification of antibody-secreting cells has been adapted for use in fish. The assay involves incubating catfish lymphocytes in 24-well plates previously coated with the antigen of interest. Cells producing antibody to the antigen leave an immunological fingerprint of bound antibody which is detected through the use of an ELISA technique to yield a colored plaque (Elisaplaque). Specificity of the assay was established by demonstrating that cells taken from fish vaccinated with an antigen exhibit the greatest response on plates coated with the given antigen. A strong positive correlation was also demonstrated between the number of Elisaplaques generated and serum agglutination titre. Using the ELISA plaque assay, it was found that antibody-secreting lymphocytes located at a different density interface and behaved differently from other lymphocyte populations when separated through discontinuous Percoll gradient centrifugation. Among the haematopoietic organs examined, the head kidney appeared to produce more antibody-secreting cells per million lymphocytes than did spleen or peripheral blood lymphocytes.