Granulocytes with ring-shaped nuclei in severe alcoholism

Myeloid dendritic cell precursors generated from bone marrow suppress T cell responses via cell contact and nitric oxide production in vitro

Tolerogenic activity of myeloid dendritic cells (DC) has so far been attributed mostly to immature or semi-mature differentiation stages but never to their precursor cells. Although myeloid suppressor cells (MSC) have been isolated ex vivo, their developmental relationship to DC and their precise phenotype remained elusive. Here, we describe the generation of MSC as myeloid DC precursors with potent suppressive activity on allogeneic and OVA-specific CD4+ and CD8+ T cell responses in vitro. These MSC appear transiently in DC cultures of bone marrow (BM) cells after 8-10 days under low GM-CSF conditions or after 3-4 days under high GM-CSF conditions. They represent CD11c- myeloid precursor cells with ring-shaped nuclei and are Gr-1low (i.e. Ly-6C+, Ly-6Glow), CD11b+, CD31+, ER-MP58+, asialoGM1+ and F4/80+. Sorted MSC develop into CD11c+ DC within 6 days. Their suppressor activity partially depends on IFN-gamma stimulation. Suppression is mediated through mechanisms requiring cell contact and nitric oxide but is independent of TNF, CD1d and TGF-beta. Together, our data describe the generation of MSC with distinct suppressor mechanisms in vitro preceding their development into immature DC.

Annular promyelocytes in acute myeloid leukemia

Granulocytes with ring-shaped nuclei (annular granulocytes; ring granulocytes) are normal bone marrow constituents in rodents. Studies in man have shown a small number of these cells in cases of myeloproliferative diseases. Myelocytes and metamyelocytes have also been described. Similar to rodents and some other animal species, the annular promyelocyte also exists in humans. The significance of these very rare cells in human haemopoiesis becomes an interesting question.