Clonal
Selection
Model
The immune response is best explained by the clonal selection mode1, which is now generally accepted. The essential features of the model are as follows: 1. The amino acid sequence of the immunoglobulin chains of an antibody is determined by a unique base sequence in the DNA of an antibody-producing cell. This amino acid sequence determines the specificity of the antibody. 2. There- exist several varieties of small lymphocytes, each of which is capable of forming only a specific antibody. What kind of antibody will be produced by a particular cell is determined before the cell comes into contact with an antigen.
3. As maturation begins, each cell type produces small amounts of a specific antibody some of this antibody binds to the cell membrane and acts as a receptor. Both B- and T- lymphocytes contain mobile antibody molecules embedded in their cell membranes, with their active sites facing outwards. Each variety of lymphocyte contains only one type of immunoglobulin receptor.
