CCL2 and precursor B-cell acute lymphoblastic leukemia: Soluble Siglec-15 (sSiglec-15) is positively correlated with various immunosuppressive cytokines in the plasma of B-ALL patients, such as MCP-1/CCL2 and IL-6, and negatively correlated with cytokines with anti-leukemic properties, such as IL-12.