Impaired Function of Fancc-/- Immune Cells.

Abstract 1494

Fanconi anemia (FA) is a genetic disorder characterized by bone marrow (BM) failure, developmental defects and cancer predisposition. Previous studies suggest that FA patients exhibit alterations in immunologic function including high levels of pro-inflammatory cytokines and increased susceptibility to bacterial and viral infections. However, it is unclear whether the immune defects observed in FA patients are immune cell autonomous or secondary to leukopenia from evolving BM failure. The aim of the current study was to determine whether FA type C deficient (Fancc-/-) macrophage exhibit impaired function and contribute to an altered inflammatory response. In this study, primary macrophage function and the inflammatory response of Fancc-/- immune cells after in vivo intraperitoneal (IP) administration of lipopolysaccharide (LPS) was assessed. Adhesion of Fancc-/- peritoneal macrophages to LPS stimulated endothelial cells was reduced compared to WT (n=3, p<0.002). Phagocytosis of IgG–labelled latex beads (n=3, p<0.004) and E.coli (n=3, p<0.04) was also impaired in Fancc-/- peritoneal macrophages compared to WT. Given these in vitro data, we next assessed whether Fancc-/- macrophage would exhibit altered function after in vivo stimulation with LPS. A low dose of LPS (1mg/kg) was injected IP into Fancc-/- and WT mice to induce a local inflammatory response. Fancc-/- mice exhibited normal neutrophil recruitment to the peritoneum, though had decreased monocyte/macrophage recruitment during the resolution phase of inflammation (n=6, p<0.001). We next questioned whether altered cytokine and chemokine production may contribute to the reduced monocyte/macrophage recruitment observed in Fancc-/- mice. Two hours after LPS treatment, peritoneal cells from Fancc-/- mice had reduced TNF-α (n=3, p<0.05) and MIP-1α (n=3, p<0.02) mRNA expression. IL-6, IL-1β, KC, and MCP-1 showed a trend towards reduction in Fancc-/- cells, though was not statistically significant. Given the overall decrease in chemokine and cytokine production in Fancc-/- mice, we evaluated the peripheral blood for altered numbers of inflammatory monocytes (CD11b⁺F4/80⁺Ly-6C^high) mobilized from the BM. LPS challenged Fancc-/- mice had a significant reduction in peripheral blood inflammatory monocytes 24 hours post LPS injection compared to WT (n=3, p<0.02). Previous published studies demonstrated that LPS stimulation of BM cells from WT mice results in expansion of monocyte/macrophage progenitors. Therefore, we questioned whether Fancc-/- BM cells exhibit altered expansion of monocyte/macrophage progenitors after in vivo LPS challenge. Colony formation in response to macrophage-colony stimulating factor (n=3, p<0.01) or granulocyte macrophage-colony stimulating factor (n=3, p<0.01) was decreased in Fancc-/- BM compared to WT after IP administration of LPS. Taken together these data suggest that the reduced replenishment of monocyte/macrophage in the local inflammatory site may be due to reduced chemokine/cytokine production, reduced mobilization of inflammatory monocytes in the peripheral blood, and decreased expansion of myeloid progenitors in the BM. Collectively, these data suggest that Fancc-/- macrophage exhibit cell autonomous immune defects.