False-colour transmission electron micrograph of a plasma cell from a reactive human lymph node. Plasma cells are mature B-lymphocytes (white blood cells) which synthesise & secrete the antibodies of the immune system. On contact with an antigen, B-lymphocytes are transformed to become first plasmablasts & then plasma cells. Characteristic of a plasma cell are the clumps of condensed chromasomal material (red) around the inner edge of the nucleus. Also typical is the network of rough endoplasmic reticulum (blue filaments) in the cytoplasm (yellow), where antibody synthesis occurs. Magnification: x3325 at 6x4.5cm size.