Specificity of antibodies in amphibian larvae possessing a small number of lymphocytes.

Tadpoles of Rana catesbiana, possessing about two million lymphocytes, were immunized with 2,4-dinitrophenyl- and 2,4,6-trinitrophenyl-conjugated bacteria and proteins, and the antibodies produced were studied by inactivation of dinitrophenyl- and trinitrophenyl-conjugated bacteriophages. Crossreactions were determined by inhibition of inactivation of modified phages with the lysine derivatives of 2,4-dinitrophenyl-,2,4,6-trinitrophenyl-, and 4-mononitrophenyl-groups. Antibodies to the two hapten-conjugates differed as significantly from each other in tadpoles as in larger animals. The ability of the small number of lymphocytes in tadpoles to discriminate between structurally similar determinants, and the estimated large number of antibodies required to cover the whole spectrum of antigenic specificities, suggests that an antigen-reactive cell changes specificity during its life time.