Long-pentraxin 3 (PTX3) is a soluble pattern recognition receptor with non-redundant functions in inflammation and innate immunity. PTX3 comprises a pentraxin-like C-terminal domain involved in complement activation via C1q interaction and an N-terminal extension with unknown functions. PTX3 binds fibroblast growth factor-2 (FGF2), inhibiting its pro-angiogenic and pro-restenotic activity. Here, retroviral transduced endothelial cells (ECs) overexpressing the N-terminal fragment PTX3-(1-178) showed reduced mitogenic activity in response to FGF2. Accordingly, purified recombinant PTX3-(1-178) binds FGF2, prevents PTX3/FGF2 interaction, and inhibits FGF2 mitogenic activity in ECs. Also, the monoclonal antibody mAb-MNB4, which recognizes the PTX3-(87-99) epitope, prevents FGF2/PTX3 interaction and abolishes the FGF2 antagonist activity of PTX3. Consistently, the synthetic peptides PTX3-(82-110) and PTX3-(97-110) bind FGF2 and inhibit the interaction of FGF2 with PTX3 immobilized to a BIAcore sensor chip, FGF2-dependent EC proliferation, and angiogenesis in vivo. Thus, the data identify a FGF2-binding domain in the N-terminal extension of PTX3 spanning the PTX3-(97-110) region, pointing to a novel function for the N-terminal extension of PTX3 and underlining the complexity of the PTX3 molecule for modular humoral pattern recognition.

Chemotaxis is defined as the directional locomotion of cells sensing a gradient of the stimulus. Some cell types, such as monocytes and neutrophils, can be considered as "professional migrants" and for many years the study of chemotaxis has been applied to these cells. However, other cell types including fibroblasts, melanoma cells, keratinocytes, and vascular endothelial cells exhibit directional locomotion in vitro.

The long pentraxin 3 (PTX3) is member of a complex superfamily of multifunctional proteins characterized by a cyclic multimeric structure. PTX3 is highly conserved in evolution and is produced by innate-immunity cells in response to proinflammatory signals and Toll-like receptor engagement. PTX3 plays complex, nonredundant functions in vivo, acting as a predecessor of antibodies, recognizing microbes, activating complement, facilitating pathogen recognition by phagocytes, and hence, playing a nonredundant role in resistance against selected pathogens. In addition, PTX3 is essential in female fertility by acting as a nodal point for the assembly of the cumulus oophorus hyaluronan-rich extracellular matrix. Thus, the prototypic long pentraxin PTX3 is a multifunctional, soluble pattern recognition receptor acting as a nonredundant component of the humoral arm of innate immunity and involved in matrix deposition and female fertility.

C-reactive protein, the first innate immunity receptor identified, and serum amyloid P component are classic short pentraxins produced in the liver. Long pentraxins, the prototype of which is PTX3, are expressed in a variety of tissues. PTX3 is produced by a variety of cells and tissues, most notably dendritic cells and macrophages, in response to TLR engagement and inflammatory cytokines. PTX3 acts as a functional ancestor of antibodies, recognizing microbes, activating complement, facilitating pathogen recognition by phagocytes, hence playing a non-redundant role in resistance against selected pathogens, in particular in the lung. Thus, the prototypic long pentraxin PTX3 is a multifunctional soluble pattern recognition receptor at the crossroads between innate immunity, inflammation, matrix deposition and female fertility.

Other than signalling receptors sustaining leucocyte recruitment during inflammatory reactions, the chemokine system includes 'silent' receptors with distinct specificity and tissue distribution. The best-characterized molecule of this subgroup is the CC chemokine receptor D6, which binds most inflammatory CC chemokines and targets them to degradation via constitutive ligand-independent internalization. Structure-function analysis and recent results with gene-targeted animals indicate that D6 has unique functional and structural features, which make it ideally adapted to act as a chemokine decoy and scavenger receptor, strategically located on lymphatic endothelium and placenta to dampen inflammation in tissues and draining lymph nodes.

Reactivation of latent human cytomegalovirus (HCMV) following allogeneic transplantation is a major cause of morbidity and mortality and predisposes to severe complications, including superinfection by Aspergillus species (spp). Antimicrobial polypeptides, including defensins and mannan-binding lectin, are known to block viral fusion by cross-linking sugars on cell surface. Pentraxin 3 (PTX3), a member of the long pentraxin family, successfully restored antifungal immunity in experimental hematopoietic transplantation. We assessed here whether PTX3 binds HCMV and murine virus (MCMV) and the impact on viral infectivity and superinfection in vivo. We found that PTX3 bound both viruses, reduced viral entry and infectivity in vitro, and protected from MCMV primary infection and reactivation as well as Aspergillus superinfection. This occurred through the activation of interferon (IFN) regulatory factor 3 (IRF3) in dendritic cells via the TLR9/MyD88-independent viral recognition sensing and the promotion of the interleukin-12 (IL-12)/IFN-gamma-dependent effector pathway.

Leukocyte recruitment has been recognized as an early event in inflammatory processes since the late 19th century. Accumulation and trafficking of leukocytes in tissues under physiological and pathological conditions are orderly (typically neutrophils precede mononuclear cells) and selective because, in certain states, one or more leukocyte subsets are recruited preferentially (e.g., eosinophils in allergy). The current paradigm of recruitment is that of a multistep process involving the action of chemotactic signals (1,2).

Thus, TIR8 represents a negative pathway of regulation of the IL-1R/TLR system, with a unique pattern of expression in epithelial cells and DC, crucial for tuning inflammation at mucosal surfaces, in particular in the gastrointestinal tract. Further research is needed to explore the role of TIR8 in controlling inflammation at other mucosal tissues and to investigate its expression and involvement in the pathogenesis of human diseases, in particular in inflammatory bowel disease.

D6 is a decoy and scavenger receptor for inflammatory CC chemokines. D6-deficient mice were rapidly killed by intranasal administration of low doses of Mycobacterium tuberculosis. The death of D6(-/-) mice was associated with a dramatic local and systemic inflammatory response with levels of M. tuberculosis colony-forming units similar to control D6-proficient mice. D6-deficient mice showed an increased numbers of mononuclear cells (macrophages, dendritic cells, and CD4 and CD8 T lymphocytes) infiltrating inflamed tissues and lymph nodes, as well as abnormal increased concentrations of CC chemokines (CCL2, CCL3, CCL4, and CCL5) and proinflammatory cytokines (tumor necrosis factor alpha, interleukin 1beta, and interferon gamma) in bronchoalveolar lavage and serum. High levels of inflammatory cytokines in D6(-/-) infected mice were associated with liver and kidney damage, resulting in both liver and renal failure. Blocking inflammatory CC chemokines with a cocktail of antibodies reversed the inflammatory phenotype of D6(-/-) mice but led to less controlled growth of M. tuberculosis. Thus, the D6 decoy receptor plays a key role in setting the balance between antimicrobial resistance, immune activation, and inflammation in M. tuberculosis infection.