Immunochemical studies on the tobacco mosaic virus protein.

The decapeptide having the amino acid sequence Thr-Thr-Ala-Glu-Thr-Leu-Asp-Ala-Thr-Arg has been shown to be a major antigenic determinant of the tobacco mosaic virus protein in rabbits, mice and guinea pigs. The antigenic specificity of the decapeptide is attributed to its C-terminal tripeptide Ala-Thr-Arg. Although this tripeptide has no demonstrable binding with antibodies to the protein, its N-octanoylated derivative exhibits specific binding with antibodies as well as the capacity to elicit delayed skin reactions in guinea pigs immunized with the protein. The latter results suggest that both B cells and T cells have antigen receptors of identical specificities. Although all mouse strains tested responded equally to TMVP, with the production of anti-protein, the response to the decapeptide was shown to be correlated (albeit not absolutely) with Ig allotype Iga exhibiting generally high responsiveness while Igb exhibiting generally low responsiveness. The low responsiveness could not be attributed to suppression of the secondary immune response.