Biased signaling at chemokine receptors

The expanding role of immunopharmacology: IUPHAR Review 16

Drugs targeting the immune system such as corticosteroids, antihistamines and immunosuppressants have been widely exploited in the treatment of inflammatory, allergic and autoimmune disorders during the second half of the 20th century. The recent advances in immunopharmacological research have made available new classes of clinically relevant drugs. These comprise protein kinase inhibitors and biologics, such as monoclonal antibodies, that selectively modulate the immune response not only in cancer and autoimmunity but also in a number of other human pathologies. Likewise, more effective vaccines utilizing novel antigens and adjuvants are valuable tools for the prevention of transmissible infectious diseases and for allergen-specific immunotherapy. Consequently, immunopharmacology is presently considered as one of the expanding fields of pharmacology. Immunopharmacology addresses the selective regulation of immune responses and aims to uncover and exploit beneficial therapeutic options for typical and non-typical immune system-driven unmet clinical needs. While in the near future a number of new agents will be introduced, improving the effectiveness and safety of those currently in use is imperative for all researchers and clinicians working in the fields of immunology, pharmacology and drug discovery. The newly formed ImmuPhar (http://iuphar.us/index.php/sections-subcoms/immunopharmacology) is the Immunopharmacology Section of the International Union of Basic and Clinical Pharmacology (IUPHAR, http://iuphar.us/). ImmuPhar provides a unique international expert-lead platform that aims to dissect and promote the growing understanding of immune (patho)physiology. Moreover, it challenges the identification and validation of drug targets and lead candidates for the treatment of many forms of debilitating disorders, including, among others, cancer, allergies, autoimmune and metabolic diseases.

CCR5 susceptibility to ligand-mediated down-modulation differs between human T lymphocytes and myeloid cells

CCR5 is a chemokine receptor expressed on leukocytes and a coreceptor used by HIV-1 to enter CD4(+) T lymphocytes and macrophages. Stimulation of CCR5 by chemokines triggers internalization of chemokine-bound CCR5 molecules in a process called down-modulation, which contributes to the anti-HIV activity of chemokines. Recent studies have shown that CCR5 conformational heterogeneity influences chemokine-CCR5 interactions and HIV-1 entry in transfected cells or activated CD4(+) T lymphocytes. However, the effect of CCR5 conformations on other cell types and on the process of down-modulation remains unclear. We used mAbs, some already shown to detect distinct CCR5 conformations, to compare the behavior of CCR5 on in vitro generated human T cell blasts, monocytes and MDMs and CHO-CCR5 transfectants. All human cells express distinct antigenic forms of CCR5 not detected on CHO-CCR5 cells. The recognizable populations of CCR5 receptors exhibit different patterns of down-modulation on T lymphocytes compared with myeloid cells. On T cell blasts, CCR5 is recognized by all antibodies and undergoes rapid chemokine-mediated internalization, whereas on monocytes and MDMs, a pool of CCR5 molecules is recognized by a subset of antibodies and is not removed from the cell surface. We demonstrate that this cell surface-retained form of CCR5 responds to prolonged treatment with more-potent chemokine analogs and acts as an HIV-1 coreceptor. Our findings indicate that the regulation of CCR5 is highly specific to cell type and provide a potential explanation for the observation that native chemokines are less-effective HIV-entry inhibitors on macrophages compared with T lymphocytes.