Cellular and humoral aspects of the primary immune response of the toad, Bufo marinus.

The primary immune response of the toad, , to flagella has been analysed in terms of three immunological parameters: (a) the kinetics of appearance and morphology of cells producing specific antibodies; (b) antigen retention in one of the lymphoid organs, the jugular bodies; and (c) the nature of the immunoglobulins produced. It was found that toads responded to the bacterial antigen by producing antibody-forming cells and serum antibody in quantities comparable to those observed in mammals. In the early phase of antibody production, small and medium lymphocytes played an important role in antibody synthesis. In the later stages of the response, large cells which resembled immature plasma cells were the predominant producers of antibody. Studies on the incorporation of tritiated thymidine suggested that the majority of antibody-forming cells observed during the logarithmic phase of the response arose by division. Electron microscopic studies showed that the localization of radioactively-labelled antigen in the jugular bodies was similar to the follicular localization in mammalian lymph nodes, i.e. the antigen was associated with the surfaces of cells, rather than with intracellular sites. Although the toad was found to possess distinct classes of 18S and 7S immunoglobulins, antibody activity to this antigen was present only in the 18S molecules. These results are consistent with the hypothesis that the major patterns of differentiation and proliferation of immunologically competent cells, antigen retention and immunoglobulin structure have emerged by the phylogenetic level of anuran amphibians.