Sequential expression of CD34 and CD33 antigens on myeloid colony-forming cells.

The expression of CD33 and CD34 antigens on human bone marrow cells was examined by fluorescence-activated cell sorting and colony assays. A marked difference of antigen expression was observed on sorted progenitors of the granulocyte/macrophage lineage (CFU-GM) with respect to enrichment and maturation status. Single-color cell sorting revealed no difference of enrichment by anti-CD33 antibody between day-7 and d-14 progenitors, while anti-CD34 antibody preferentially enriched d-14 colony-forming units (CFU).

Prevention of human helper T-cell clone activation by cyclosporin A also blocks secretion of granulocyte/macrophage colony stimulating activity.

Cyclosporin A (CsA) blocks stimulation and growth of alloreactive T helper cell clones (Th-TCC), even in the presence of exogenous Interleukin-2 (IL-2). To examine whether this might reflect a generalised inhibition of cytokine production by these cells, their production of granulocyte/macrophage colony-stimulating factors (GM-CSF), thought not to be involved in the autocrine proliferation of the clones themselves, was investigated. Contrary to the prediction that only pathways relevant to T cell clonal expansion would be blocked by CsA, it was found that this immunosuppressive substance exerted a profound inhibitory activity on GM-CSF secretion, even in the presence of exogenous IL-2.