Mechanism of action of the viral chemokine-binding protein E163 from ectromelia virus

The chemokine receptor CCR5: multi-faceted hook for HIV-1

Chemokines are cytokines whose primary role is cellular activation and stimulation of leukocyte migration. They perform their various functions by interacting with G protein-coupled cell surface receptors (GPCRs) and are involved in the regulation of many biological processes such as apoptosis, proliferation, angiogenesis, hematopoiesis or organogenesis. They contribute to the maintenance of the homeostasis of lymphocytes and coordinate the function of the immune system. However, chemokines and their receptors are sometimes hijacked by some pathogens to infect the host organism. For a given chemokine receptor, there is a wide structural, organizational and conformational diversity. In this review, we describe the evidence for structural variety reported for the chemokine receptor CCR5, how this variability can be exploited by HIV-1 to infect its target cells and what therapeutic solutions are currently being developed to overcome this problem.

Detection of Chemokine Binding Proteins Association to Cell Surface Glycosaminoglycans by Flow Cell Cytometry and Indirect Immunofluorescence

Viruses encode secreted proteins that bind chemokines to modulate their activity. Viral proteins may simultaneously interact with glycosaminoglycans allowing these proteins to be anchored at the cell surface to increase their anti-chemokine activity in the proximity of infection. Here we describe methodology to evaluate the interaction of viral secreted proteins with cell-surface glycosaminoglycans by immunofluorescence and detection by flow cytometry or microscopy. These methods could be equally applied to other chemokine binding proteins that do not have viral origin.

Virus-encoded cytokine and chemokine decoy receptors

Poxviruses and herpesviruses encode secreted versions of cytokine receptors as a unique strategy to evade the host immune response. Recent advances in the field have shown the great impact of some of these proteins in immune modulation and viral pathogenesis, and have uncovered unique properties of these viral proteins not found in the cellular counterparts. These modifications inspired by viruses lead to improved immune modulatory activity of the soluble cytokine receptors, information that has been used to develop more efficient therapeutics to treat inflammatory conditions.

Targeting Chemokine-Glycosaminoglycan Interactions to Inhibit Inflammation

Leukocyte migration into tissues depends on the activity of chemokines that form concentration gradients to guide leukocytes to a specific site. Interaction of chemokines with their specific G protein-coupled receptors (GPCRs) on leukocytes induces leukocyte adhesion to the endothelial cells, followed by extravasation of the leukocytes and subsequent directed migration along the chemotactic gradient. Interaction of chemokines with glycosaminoglycans (GAGs) is crucial for extravasation in vivo. Chemokines need to interact with GAGs on endothelial cells and in the extracellular matrix in tissues in order to be presented on the endothelium of blood vessels and to create a concentration gradient. Local chemokine retention establishes a chemokine gradient and prevents diffusion and degradation. During the last two decades, research aiming at reducing chemokine activity mainly focused on the identification of inhibitors of the interaction between chemokines and their cognate GPCRs. This approach only resulted in limited success. However, an alternative strategy, targeting chemokine-GAG interactions, may be a promising approach to inhibit chemokine activity and inflammation. On this line, proteins derived from viruses and parasites that bind chemokines or GAGs may have the potential to interfere with chemokine-GAG interactions. Alternatively, chemokine mimetics, including truncated chemokines and mutant chemokines, can compete with chemokines for binding to GAGs. Such truncated or mutated chemokines are characterized by a strong binding affinity for GAGs and abrogated binding to their chemokine receptors. Finally, Spiegelmers that mask the GAG-binding site on chemokines, thereby preventing chemokine-GAG interactions, were developed. In this review, the importance of GAGs for chemokine activity in vivo and strategies that could be employed to target chemokine-GAG interactions will be discussed in the context of inflammation.

A virus-encoded type I interferon decoy receptor enables evasion of host immunity through cell-surface binding

Soluble cytokine decoy receptors are potent immune modulatory reagents with therapeutic applications. Some virus-encoded secreted cytokine receptors interact with glycosaminoglycans expressed at the cell surface, but the biological significance of this activity in vivo is poorly understood. Here, we show the type I interferon binding protein (IFNα/βBP) encoded by vaccinia and ectromelia viruses requires of this cell binding activity to confer full virulence to these viruses and to retain immunomodulatory activity. Expression of a variant form of the IFNα/βBP that inhibits IFN activity, but does not interact with cell surface glycosaminoglycans, results in highly attenuated viruses with a virulence similar to that of the IFNα/βBP deletion mutant viruses. Transcriptomics analysis and infection of IFN receptor-deficient mice confirmed that the control of IFN activity is the main function of the IFNα/βBP in vivo. We propose that retention of secreted cytokine receptors at the cell surface may largely enhance their immunomodulatory activity.