The common lymphoid precursor matures into lymphocytes, including В and T cells which generate adaptive immune responses.
В cells and T cells. В cells develop in the bone marrow. T cell precursors leave the bone marrow and mature in the thymus. В and T lymphocytes cannot be distinguished morphologically – both are small cells with condensed chromatin and few cytoplasmic organelles. В and T lymphocytes can be distinguished by assessing expression of lineage-specific molecules. Mature В and T cells circulate between the blood and peripheral lymphoid tissues. Encounter with antigen triggers proliferation and differentiation into cells with specialised effector functions. Both В and T cells have a large repertoire of receptors that can recognise a wide diversity of antigens.
Plasma cells. В cells mature into plasma cells, terminally differentiated cells which secrete antibody.
NK cells. NK cells are large granular lymphocytes found throughout the tissues of the body but predominantly in the circulation. They lack antigen-specific receptors and are part of the innate immune system. NK cells kill tumour cells and virus-infected cells.
