Plasma cells produce specific antibodies by the process of?
Clonal selection

B-cells are able to make a specific antibody against a specific antigen. It is due to the presence of specific receptor on B-cells - B-cell receptor (BCR), that is usually an immunoglobulin Ig M or Ig D. An antigen interacts with B-cell that shows best fit by virtue of its BCR. The antigen binds to this receptor, and the B-cell is stimulated to divide and form a clone (clonal selection). This clone of cells will become plasma cells that will secrete antibody of a particular specificity and same class.
Plasma cells make an antibody of a single specificity, of a single immunoglobulin class and allotype, and of a single light chain type only. An exception is seen in the primary antibody response, when a plasma cell producing IgM initially, may later be switched to IgG production (called isotype switching or class switching).
Class selection
Clonal selection
Isotope selection
Isotope switching