Phylogenetic studies on the immune response. I. Localization of antigens and immune response in the toad, Bufo marinus

Abstract

Toads of the species Bufo marinus were injected subcutaneously with ¹²⁵I-labelled flagella from Salmonella adelaide. Observations were made on the ensuing serum antibody response, the antigen localization pattern and sequential cellular changes in lymphatic and other tissues.

The serum antibody findings confirmed the work of previous investigators in showing a good primary response, prolonged synthesis of mercaptoethanol sensitive antibody and little or no evidence of secondary responsiveness.

Antigen became localized in the jugular bodies and spleen where proliferation of pyroninophilic cells could be observed after 5 days. Both the antigen-trapping cells and the first pyroninophilic blasts were scattered randomly throughout the jugular bodies. There was no clear-cut separation into cortex and medulla. Nothing resembling the antigen-trapping web of rat lymph node follicles was observed, nor were there any germinal centres. In the spleen, antigen was trapped in the red pulp and some degree of concentration around the islands of white pulp could be noted 1 day later. However, unlike in the rat, entry of antigen into the white pulp did not occur.

Both focal and diffuse collections of lymphoid and pyroninophilic cells were found in the kidney after antigenic stimulation. It seems likely that the kidney is a major antibody-forming organ in the toad.

The hypothesis is advanced that the absence of immunological memory may be due to the absence of the follicular antigen-trapping web and of resultant germinal centres.