CD56 (Natural Killer Cells)

CD56 marks human natural killer (NK) cells, which provide innate immune surveillance. CD56bright NK cells, mainly in lymphoid tissues, secrete cytokines (IFN-γ, TNF) to regulate immune responses. CD56dim NK cells, predominant in blood, are highly cytotoxic—killing virus-infected and tumor cells via perforin/granzymes and antibody-dependent cellular cytotoxicity. NKs also shape adaptive immunity and respond rapidly without prior sensitization.

Tumors positive for CD56 (NCAM) include neuroendocrine neoplasms — small cell lung carcinoma, carcinoid tumors, medullary thyroid carcinoma, neuroblastoma, and Merkel cell carcinoma; hematologic malignancies — NK‑cell and NK/T‑cell lymphomas and many multiple myelomas; and some acute myeloid leukemias. CD56 is a neural/neuroendocrine and NK‑cell marker, so expression is seen in tumors of those lineages.

CD56 positivity means cells express the CD56 (NCAM) surface marker, commonly identifying natural killer (NK) cells and some T‑cell subsets. In clinical testing, CD56+ can indicate an NK‑cell population or abnormal expression seen in certain hematologic malignancies (some leukemias/lymphomas) and neuroendocrine tumors. Interpretation depends on cell type and other markers; clinical correlation and further testing are needed.

CD56 is the cluster-of-differentiation name for the neural cell adhesion molecule (NCAM, also called NCAM1), a cell-surface glycoprotein involved in adhesion, migration and signaling. It’s expressed on natural killer (NK) cells, subsets of T cells and neuronal tissues. NCAM has multiple isoforms (e.g., 120, 140, 180 kDa) important in neural development and immune recognition.

CD56 (NCAM) is expressed on NK cells and neural and neuroendocrine tissues. High or aberrant CD56 expression is linked to NK‑cell leukemias and extranodal NK/T‑cell lymphoma, some acute leukemias and AML subsets, and multiple myeloma (with prognostic significance). CD56 is also found on neuroendocrine and neural tumors such as neuroblastoma and small‑cell lung cancer. Altered CD56+ NK cell subsets appear in certain infections and autoimmune diseases.

Natural killer (NK) cells are generally beneficial: they’re innate immune cells that rapidly detect and destroy virus-infected and cancerous cells and help shape immune responses. However, when overactive or misdirected they can cause tissue damage and contribute to inflammatory or autoimmune conditions. Overall they’re crucial for early defense but must be properly regulated to avoid harm.