CD56bright

CD56bright refers to a subset of natural killer (NK) cells defined by high surface expression of CD56 and low or absent expression of CD16 (FcγRIII). In humans, CD56bright NK cells are relatively enriched in secondary lymphoid tissues such as lymph nodes and tonsils, while they represent a smaller fraction of NK cells in peripheral blood compared with the CD56dim subset.

Phenotypically, CD56bright NK cells express markers that favor lymphoid-tissue homing, including CD62L and CCR7. They generally have lower levels of perforin and granzymes than CD56dim NK cells and are typically CD16-negative, although a minority may express CD16. This profile aligns with their functional specialization.

Functionally, CD56bright NK cells are prolific producers of cytokines, including IFN-γ, TNF-α, and GM-CSF, in response to inflammatory cytokines such as IL-12, IL-15, and IL-18. They exhibit less natural cytotoxicity in standard assays but have a high proliferative capacity and can respond vigorously to cytokine stimulation. With activation, they can differentiate into the more cytotoxic CD56dim subset, contributing to effector functions in peripheral blood.

Development and biology-wise, CD56bright cells are viewed as an earlier developmental stage within human NK cells and are thought to participate in shaping adaptive immune responses through their cytokine output and interactions with other immune cells, including dendritic cells.

Clinical relevance, while still under investigation, includes shifts in the CD56bright/CD56dim balance in health and disease. Alterations have been reported in infections, cancer, and autoimmune conditions, and therapies that expand or modulate this subset are of ongoing interest in immunotherapy and infectious disease management.