Abstract
(Englisch)
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In the past 3 years tremendous progress has been achieved in the field of chemokines. The most outstanding findings are
a) the connection between chemokines/chemokine receptors and HIV infection, and
b) the recognition of functionally distinct chemokine subfamilies
In short, certain chemokine receptors, notably CXCR4 and CCR5, were identified as HIV co-receptors which together with CD4 mediate entry of HIV particles into target cells. This discovery provided a missing link in the puzzle of HIV transmission and pathogenesis. Importantly, the chemokines that bind to CXCR4 and CCR5 were found to be potent inhibitors of HIV infection, thereby providing an novel strategy for the development of anti-HIV therapeutics.
The two major functionally distinct chemokine subfamilies include the 'inflammatory' and the 'housekeeping' chemokines. The field of chemokines got started with those that are produced at sites of inflammation and disease, i.e., those that regulate the recruitment of effector leukocytes under inflammatory conditions. Members of the novel subfamily, the housekeeping chemokines, differ fundamentally from inflammatory chemokines in their constitutive production at discrete locations in primary and secondary lymphoid tissues and their effects on resting, circulating lymphocytes. Recent studies indicate that housekeeping chemokines regulate the traffic of lymphocytes at sites of lymphopoiesis (bone marrow, thymus), antigen priming (lymph node, Peyer's patches, spleen), and immune surveillance (non-lymphoid tissues).
My laboratory has been active in both areas, as documented by numerous publications (see attachment: 'Own contributions to the field of human chemokines and HIV infection).
The activities within the BBW grant proposal were focused on the chemokine receptor CXCR3 which regulates the recruitment of effector T lymphocytes to T cell-dependent inflammatory diseases. We have cloned CXCR3 from a human T cell cDNA library and determined its specificity for three IFN-g-regulated chemokines IP10, Mig and I-TAC. CXCR3 is predicted to be a seven transmembrane domain receptor of 368 amino acids, and, importantly, is highly induced on T lymphocytes activated in vitro by culturing in the presence of IL-2. CXCR3 is not present on any other type of leukocytes, suggesting that this receptor and the chemokines it binds provide an exceptionally selective system for the traffic of effector T cells at sites of disease. In agreement, CXCR3-positive T cells were found to be numerous in many inflammatory disorders, including rheumatoid arthritis, ulcerative colitis, and sarcoidosis.
Leukocyte traffic across blood vessel endothelia and through tissues depends largely on adhesive interactions. For leukocyte arrest and firm adhesion to endothelia and extracellular matrix, integrins need to be activated. This process is mediated through signaling via G protein coupled receptors, such as chemokine receptors.
We have examined the role of CXCR3 in induction of T lymphocyte adhesion to integrin ligands. Both IP10 and Mig were potent inducers of T lymphocyte adhesion to immobilized integrin ligands fibronectin, intracellular adhesion molecule 1 (ICAM-1), and vascular cell adhesion molecule 1 (ICAM-1). In agreement with CXCR3 expression, IL-2-cultured but not resting T lymphocytes responded to chemokine stimulation. Adhesion induction was both rapid and transient, and occurred at low nanomolar (physiological) concentrations of IP10 and Mig. We have shown that both chemokines were produced and presented in an active form by cultured umbilical vein endothelial cells (HUVEC) after stimulation with IFN-g and TNFa. Capturing on endothelial cells probably involved binding to sulfated proteoglycans which are thought to play a crucial role in leukocyte responses to chemokines in vivo. IFN-g/TNFa-stimulated HUVEC allowed adhesion of IL-2-treated T lymphocytes, and this effect was substantially blocked by anti-CXCR3 antibodies, suggesting the involvement of IP10 and Mig expressed on HUVEC.
This is the first demonstration that chemokines are able to induce integrin-mediated adhesion in effector T lymphocytes, i.e., in those T lymphocytes which participate in inflammatory responses and suggests a critical role of IP10 and Mig in IFN-g-dependent pathologies.
In Progress: We are engaged in a collaborative study with the laboratory of Dr. R. Pardi at the Scientific Institute San Raffaele in Milano, involving the chemokine production by macrophages which have been exposed to different strains of M. tuberculosis or fragments thereof. A manuscript describing the findings is in preparation.
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