They are not able to attack just any pathogen, as phagocytes are. They are programmed to go after specific pathogens. They also bear the major responsibility for the actions of the immune system. The two major classes of lymphocytes are B cells, which reach maturity in the bone, and T cells, which reach maturity in the thymus. Both of these recognize specific pathogens.
B cells work by producing, transporting, and secreting antibodies.
Upon meeting a pathogen, B cells begin dividing and releasing antibodies, which seek out and destroy the pathogen. Each B cell makes one specific antibody for one specific pathogen. If a B cell meets another pathogen, nothing can be done. One type of T cell, a helper T cell, must be involved for a B cell to destroy pathogens. T cells can help B cells or other T cells, or directly attack pathogens.