Cell adaptation to hypoxia (Hyp) requires activation of transcriptional programs that coordinate expression of genes involved in oxygen delivery (via angiogenesis) and metabolic adaptation (via glycolysis). Here, we describe that oxygen availability is a determinant parameter in the setting of chemotactic responsiveness to stromal-derived factor 1 (CXCL12). Low oxygen concentration induces high expression of the CXCL12 receptor, CXC receptor 4 (CXCR4), in different cell types (monocytes, monocyte-derived macrophages, tumor-associated macrophages, endothelial cells, and cancer cells), which is paralleled by increased chemotactic responsiveness to its specific ligand. CXCR4 induction by Hyp is dependent on both activation of the Hyp-inducible factor 1 α and transcript stabilization. In a relay multistep navigation process, the Hyp–Hyp-inducible factor 1 α–CXCR4 pathway may regulate trafficking in and out of hypoxic tissue microenvironments.

To identify the molecular basis underlying the functions of tumor-associated macrophages (TAMs), we characterized the gene expression profile of TAMs isolated from a murine fibrosarcoma in comparison with peritoneal macrophages (PECs) and myeloid suppressor cells (MSCs), using a cDNA microarray technology. Among the differentially expressed genes, 15 genes relevant to inflammation and immunity were validated by real-time polymerase chain reaction (PCR) and protein production. Resting TAMs showed a characteristic gene expression pattern with higher expression of genes coding for the immunosuppressive cytokine IL-10, phagocytosis-related receptors/molecules (Msr2 and C1q), and inflammatory chemokines (CCL2 and CCL5) as expected, as well as, unexpectedly, IFN-inducible chemokines (CXCL9, CXCL10, CXCL16). Immunohistology confirmed and extended the in vitro analysis by showing that TAMs express M2-associated molecules (eg, IL-10 and MGL1), as well as CCL2, CCL5, CXCL9, CXCL10, and CXCL16, but no appreciable NOS2. Lipopolysaccharide (LPS)-mediated activation of TAMs resulted in defective expression of several proinflammatory cytokines (eg, IL-1β, IL-6, TNF-α) and chemokines (eg, CCL3), as opposed to a strong up-regulation of immunosuppressive cytokines (IL-10, TGFβ) and IFN-inducible chemokines (CCL5, CXCL9, CXCL10, CXCL16). Thus, profiling of TAMs from a murine sarcoma revealed unexpected expression of IFN-inducible chemokines, associated with an M2 phenotype (IL-10^high, IL-12^low), and divergent regulation of the NF-κB versus the IRF-3/STAT1 pathway.

The innate immune system consists of a cellular and a humoral arm. Pentraxins (e.g., the short pentraxin C reactive protein and the long pentraxin PTX3) are key components of the humoral arm of innate immunity which also includes complement components, collectins, and ficolins. In response to microorganisms and tissue damage, neutrophils, macrophages, and dendritic cells are major sources of fluid-phase pattern-recognition molecules (PRMs) belonging to different molecular classes. Humoral PRMs in turn interact with and regulate cellular effectors. Effector mechanisms of the humoral innate immune system include activation and regulation of the complement cascade; agglutination and neutralization; facilitation of recognition via cellular receptors (opsonization); and regulation of inflammation. Thus, the humoral arm of innate immunity is an integrated system consisting of different molecules and sharing functional outputs with antibodies.

The long pentraxin (PTX) 3 is produced by macrophages and myeloid dendritic cells in response to Toll-like receptor agonists and represents a nonredundant component of humoral innate immunity against selected pathogens. We report that, unexpectedly, PTX3 is stored in specific granules and undergoes release in response to microbial recognition and inflammatory signals. Released PTX3 can partially localize in neutrophil extracellular traps formed by extruded DNA. Eosinophils and basophils do not contain preformed PTX3. PTX3-deficient neutrophils have defective microbial recognition and phagocytosis, and PTX3 is nonredundant for neutrophil-mediated resistance against Aspergillus fumigatus. Thus, neutrophils serve as a reservoir, ready for rapid release, of the long PTX3, a key component of humoral innate immunity with opsonic activity.