Overview

Plasma cells are oval cells (≈ 10–20 µm) with an eccentric round nucleus whose coarse heterochromatin is arranged in a "clock-face" or "cartwheel" pattern. Their cytoplasm is deeply basophilic because of extensive rough endoplasmic reticulum, with a pale perinuclear "hof" marking a large Golgi apparatus — the morphology of a professional protein-secreting cell. Each secretes thousands of antibody molecules per second, all of a single specificity and isotype. Unlike B cells they have lost most surface immunoglobulin, CD20 and MHC class II, and are identified by CD138 (syndecan-1) and strong CD38 expression.

Short-lived plasmablasts form within days of antigen exposure in extrafollicular sites (medullary cords of lymph nodes, splenic red pulp) and secrete mostly IgM. Germinal-centre-derived long-lived plasma cells migrate to survival niches in the bone marrow (supported by CXCL12, IL-6 and APRIL) and continue to secrete high-affinity antibody for years or decades, maintaining protective serum antibody after infection or vaccination. Many IgA plasma cells reside in the lamina propria of mucosae. Accumulations of immunoglobulin may be seen as cytoplasmic Russell bodies or intranuclear Dutcher bodies.

Location: Medullary cords of lymph nodes, splenic red pulp, bone marrow (normally < 5% of nucleated cells), gut and airway lamina propria; very rarely in blood.

Anatomy

Histology: Eccentric nucleus with clock-face chromatin, basophilic cytoplasm (abundant RER), perinuclear clearing (Golgi). Methyl-green pyronin stains the RNA-rich cytoplasm red.

Function

Synthesise and secrete large amounts of antibody (humoral immunity).
Maintain long-term serum antibody levels ("serological memory") from bone-marrow niches.
Provide mucosal IgA (lamina-propria plasma cells).

Clinical significance

Multiple myeloma

Malignant proliferation of a single plasma-cell clone in the bone marrow (≥ 10% clonal plasma cells) producing a monoclonal immunoglobulin (M-protein/paraprotein — usually IgG, then IgA) and/or free light chains (Bence Jones proteinuria). Features — CRAB: hyperCalcaemia, Renal impairment (light-chain cast nephropathy), Anaemia (with rouleaux) and Bone lytic lesions ("pepper-pot" skull, pathological fractures) — plus infections from suppression of normal immunoglobulins and sometimes AL amyloidosis or hyperviscosity. Treated with proteasome inhibitors (bortezomib), immunomodulators, anti-CD38 antibodies (daratumumab) and stem-cell transplantation.

MGUS

Monoclonal gammopathy of undetermined significance: M-protein < 30 g/L, < 10% marrow plasma cells and no myeloma-defining features; common in older adults and progresses to myeloma or related disease at ≈ 1% per year.

Mnemonics

Myeloma — "CRAB"

HyperCalcaemia, Renal failure, Anaemia, Bone lesions.

Compiled from standard anatomy and physiology references — see the Lymphatic & Immune System sources. For education only; not medical advice.