CD56(bright) cells differ in their KIR repertoire and cytotoxic features from CD56(dim) NK cells

In this study we present new differential characteristics of NK cells expre ssing CD56 surface antigen in low (CD56(dim)) or high (CD56(bright)) densit y. In contrast to CD56(bright) NK cells CD56(dim) cells express killer cell immunoglobulin (Ig)-like receptors (KIR) such as CD158a, CD158b, and NKB1. However, c-type lectin-like receptors (KLR) CD94/NKG2 and CD161 are presen t on both subsets. The ability to form conjugates with susceptible targets is approximately twice as strongly pronounced in CD56(dim) VS. CD56(bright) NK cells. Last but not least, granules of CD56(dim) cells contain about te nfold more perforin and granzyme A enabling potentially more effective cyto lysis compared to CD56(bright) NK cells. On the other hand, CD56(bright) NK cells are superior in producing the proinflammatory cytokines IFN-gamma (2 8.5% vs. 20.8%, p <0.05) and TNF-alpha (28% vs. 15.8%, p <0.001). The diffe rent NK cell populations retained their specific phenotype in vitro during culture in the presence of IL-2 contradicting that they simply display diff erent stages of maturity. Taken together our data support the view that CD5 6 bright cells are specialized NK cells that regulate immunological respons e mechanisms rather by cytokine supply than by their cytotoxic potential. T he poor cytolytic capacity of CD56 bright NK cells can be explained by weak ability in forming conjugates with target cells and low contents of perfor in and granzyme A in their granules.