Expression of stem cell inhibitor (SCI) gene in patients with bone marrow failure

Stem cell inhibitor (SCI) has been shown to inhibit the proliferation of primitive progenitors. The inhibitor, a product of bone marrow macrophages, activated lymphocytes, and monocytes, is identical to macrophage inflammatory protein (MIP-1 alpha). We report homologous (SCI/hMIP-1 alpha) sequences in freshly isolated lymphocytes, monocytes, and granulocytes and have found that SCI mRNA can be induced in monocytes by lipopolysaccharide (LPS) and interleukins 1, 2, and 6. In contrast, interferon gamma (IFN-gamma) decreases the expression of SCI/hMIP-1 alpha. Although only a low level expression of SCI/hMIP-1 alpha mRNA can be detected in normal human bone marrow nucleated cells (NCBM), very significant increases in the levels of SCI/hMIP-1 alpha RNA transcripts are observed in NCBM from patients with aplastic anemia (AA) and myelodysplastic syndrome (MDS). These data suggest that the expression of SCI/hMIP-1 alpha in bone marrow may reflect dysregulated cytokine production and activation of the immune system that may possibly contribute to disease progression.