Antibodies are made by B lymphocytes and exist in 2 forms - either membrane bound or secreted. B lymphocytes use membrane bound antibody to interact with antigens. The clone will continue making antibody of the same specificity. Simultaneously, there will be lots of other clones of different specificity. This is known as a polyclonal response.
Antigens have determinants called epitopes.
Epitopes are molecular shapes recognized by antibodies, which recognise 1 epitope rather than whole antigen. B lymphocytes evolve into plasma cells under the influence of T cell released cytokines. Plasma cells secrete antibodies in greater amounts, but do not divide. They exist in lymphoid tissues, not blood. Other B cells circulate as memory cells.