Transmission electron micrograph (TEM) of the ultrastructure of a plasma cell. Plasma cells are derived from B cell lymphocytes. Plasma cells can be likened to antibody factories synthesizing and secreting immunoglobulins at high intensity. Reflecting very active protein production the plasma cell cytoplasm contains abundant rough endoplasmic reticulum (rough ER). The polypeptides being assembled by the rough ER are seen as particulate material within the membranous cisternae. Magnification: x10,000 when width printed at 10cm.