Plasma cells (plasmacytes) are immunocompetent cells producing and secreting antibodies (immunoglobulins IgM, IgG, IgA, IgE, IgD). Plasma cells are formed from antigen-activated B cells.

TEM image, 15,000X. In a mature plasma cell, the nucleus is eccentric, it contains nucleoli #1, #2, euchromatin, and some clumps of heterochromatin peripherally. The greater part of the cytoplasm is occupied by numerous and somewhat dilated cisterns of rough endoplasmic reticulum #1, #2, which are filled by proteins produced by the cell. The cytoplasm also comprises a well-developed Golgi apparatus (in conventional microscopy, it is defined as a pale zone), as well as mitochondria #1, #2.

TEM image, 20,000X (photo courtesy of L. P. Bobova). In plasma cells, acceleration of biosynthesis and secretion of immunoglobulins is accompanied by a significant enlargement of cisterns in rough endoplasmic reticulum #1, #2 thus, a considerable amount of products is accumulated there. The structure of Golgi apparatus and its architecture are in line with the state of a high functional cell activity.