Phenotype and function of a CD56+peripheral blood monocyte

G-CSF primed CD34 cells cultured for 2-3 weeks in IL-2 and stem cell factor generate CD56(high) cells with phenotypic and morphologic features of NK cells, and a novel adherent CD56(low) CD16-population expressing myeloid markers (CD33 and HLA-DR). We hypothesized that similar cells might also occur in peripheral blood. In 13/13 normal individuals, we found a circulating population of CD56 (low), CD33 +, FcgammaRI +, FcgammaRII +, HLA-DR +, CD11b(high), CD14 + monocytes closely resembling the cultured CD56(low) CD33 + cells. They may represent a normal counterpart of the CD56 + CD33 + hybrid myeloid/natural killer cell leukemia. Their mean frequency was 1.3+/-1% (standard deviation), range 0.16-3.5%, of total mononuclear cells. CD56(low) CD33 + cells, primed with cytomegalovirus antigen, induced autologous T-lymphocyte proliferation comparably to CD56-, CD14 + peripheral blood monocytes (PBM). Conversely, CD56(low) cells induced greater T-cell proliferation than CD56- PBM when lymphocyte responders were HLA mismatched. Unstimulated CD56(low) CD33 + cells showed a low antiproliferative effect on K562, which was increased upon LPS stimulation. The pattern of cytokine production by CD56(low) CD33 + cells and PBM largely overlapped; however, they produced detectable levels of IL-6 and IL-1beta. These results define a minor monocyte population with distinct phenotypic and functional features.