Plasmacytic

Plasmacytic is an adjective relating to plasma cells, the antibody-producing cells of the immune system derived from B lymphocytes. In normal physiology, plasma cells reside primarily in bone marrow and, to a lesser extent, in lymphoid tissues. They are typically described microscopically as oval or round cells with an eccentrically placed nucleus showing clock-face chromatin, abundant basophilic cytoplasm, and a clear perinuclear zone corresponding to the Golgi apparatus.

In pathology, the term is used to describe cells or tissue features with plasmacytic differentiation or infiltration. This can occur in reactive conditions, such as chronic infections and inflammatory diseases, where polyclonal plasma cells expand. It is also used in reference to neoplastic processes driven by clonal plasma cells, including plasmacytoma (a solitary tumor of plasma cells that may arise in bone, called solitary bone plasmacytoma, or in soft tissue, extramedullary plasmacytoma) and systemic diseases such as multiple myeloma.

Diagnosis relies on morphologic assessment, immunophenotyping, and detection of monoclonality. Plasma cells typically express CD38 and CD138 and show light chain restriction (kappa or lambda). Serum or urine protein studies may reveal a monoclonal protein (M protein). Bone marrow examination often shows clonal plasma cell expansion in myeloma, with cytogenetic abnormalities providing prognostic information. Plasmacytic features can therefore indicate either reactive or neoplastic processes, guiding clinical management.