Evolution in mammals has led to expansion of the antibody gene pool and a mechanism for generating a vast number of antibodies with a wide range of different specificities. This large repertoire of different antibody specificities arms the immune system to respond to practically all of the potential antigens nature can devise. Antibodies work in three ways. During an immune response, a complex lattice of interlinked antigens and antibodies, known as an immune complex , will present an array of constant regions which can activate the various cells mentioned above through ligation of their immunoglobulin receptors. These cells have receptors for antigen and confer specificity on an immune response.
Lymphocytes express receptors with varying affinity for the antigen in question.
The cell with the highest affinity for the most abundant antigen will have growth advantage and will preferentially generate progeny of itself. This process is called clonal expansion and is antigen driven. B lymphocytes produce antibodies and some soluble mediators called cytokines. They arise in the bone marrow in adult mammals. T lymphocytes arise in bone marrow but mature in the thymus.