Clonal Selection: Some Experiments

In 1969 the Australian immunologists Ada and Byrt reported their demonstration of

Their test antigen was a protein, flagellin, extracted from the flagella of one strain of the bacterium Salmonella adelaide and polymerized. We shall call this antigen "POL(A)".

They made the antigen highly radioactive by labelling it with the radioactive isotope 125I.

As a control, they used a preparation of polymerized flagellin isolated from a different strain of Salmonella. We shall call this "POL(B)".

Their Experiments: 1. 2.
Pretreatment of spleen cells Anti-POL(A) antibodies Anti-POL(B) antibodies
125I-POL(A) ± ++++
Nonradioactive POL(A) +++ ++++
None +++ ++++

The image on the right supports the findings of Ada and Byrt. It is an autoradiograph of lymph node cells — taken from an unimmunized ("unprimed" or "virgin") mouse — that were treated (for 15 minutes) with radioactive POL (3H-POL). Only one of the cells has bound the antigen. Presumable the others have receptors for other antigens. The bound antigen is clustered at one pole of the cell because the cell was killed before endocytosis of the antigen-receptor complexes could be completed. Image courtesy of E. Diener from E. Diener and V. H. Paetkau, Proc. Natl. Acad. Sci. U.S.A 69:2364, 1972.

In 1972 Edelman and his colleagues at Rockefeller University demonstrated the presence of antigen-specific lymphocytes in unprimed or "virgin" mice by another method. They attached an antigen to the surface of nylon fibers and then placed the fibers in a dish containing spleen cells (mostly lymphocytes) from an unimmunized mouse. A small percentage of these cells stuck to the fibers, indicating the presence of complementary antibodylike molecules on their surface. However, no cells would stick

The image is courtesy of G. M. Edelman, from U. Rutishauser, C. F. Millette, and G. M. Edelman, Proc. Nat. Acad. Sci. U.S.A. 59:1596, 1972.

Link to a discussion of the clonal selection theory supported by these experiments.

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10 January 2011