The answer is; producing a unique antibody from all other B cells by genomic rearrangement.
An isolated B cell produces monoclonal antibodies (also called Immunoglobulins). Different B cell types produce different types of antibodies (hence the serum of an animal has polyclonal antibodies). Memory B cells are developed when a particular infection is eradicated by the immune system. These B cells proliferate when the infection returns by producing the same antibodies that were effective against the foreign entity.
