Regulation of MDL-1 receptor expression. (A and B) Bone marrow cells and joint tissues show the highest level of MDL-1 expression. Quantitative PCR analysis of human (A) and mouse (B) anatomy panels generated from pooled tissue samples from at least five donors. (C) MDL-1 is expressed on murine granulocytes (CD11b + Ly6G high) and monocytes (CD11b + Ly6G low) from bone marrow and peripheral blood. Histograms in gray color are rIgG2a isotype staining controls. Data are representative of three experiments. (D) TNF but not IFN-γ promotes MDL-1 expression. Murine bone marrow cells were cultured with MCSF in the presence of IFN-γ or TNF and mRNA was isolated for MDL-1 expression analysis by Q-PCR. Cell surface expression of MDL-1 was determined by flow cytometry. Data representative of at least three separate experiments with similar results. (E) Anti–MDL-1 activates bone marrow–derived macrophages to produce TNF and G-CSF. Bone marrow cells isolated from three mice were cultured with indicated antibodies and/or LPS for 36 h. Culture supernatants were assayed for secreted cytokines by Luminex assay. * indicates significance (P < 0.01) as determined by Student’s t test. Results are representative of three separate experiments with similar results.