Regulation of chemokine gene expression in human endothelial cells by proinflammatory cytokines and Borrelia burgdorferi.

Chemokines play a central role in the process of leukocyte recruitment to tissues. By their chemotactic activity they guide leukocytes to the site of infection/injury. Chemokines have been suggested to trigger firm adhesion of leukocytes to activated endothelial cells as well as the subsequent diapedesis. For these functions, chemokines produced by EC are particularly well suited. Our experiments with proinflammatory stimuli demonstrate that chemokines are induced in EC by a variety of stimuli including inflammatory cytokines and bacterial structures such as LPS and preparations of B. burgdorferi. The induction of chemokines by all of these agents occurs rapidly and does not require new protein synthesis. Two chemokines, MCP-1 and IL-8, respond to very low doses (0.1-1 U/ml) of proinflammatory cytokines which is important at the beginning of an immune response when soluble inflammatory mediators might still be limiting. The chemokines RANTES, IP-10, and mig show synergistic induction by low doses (1 U/ml) of several inflammatory mediators, which again is important when only limiting amounts of inflammatory stimuli are present. The upregulation of six chemokine genes as well as genes encoding adhesion molecules in two cell types, EC and fibroblasts, by B. burgdorferi suggests that chemokines might play a central role in the regulation of spirochete-induced inflammatory responses and the subsequent immune responses. Recent evidence suggests that T cells with pathogenic potential contribute to chronic inflammation at the late stage of Lyme disease. Therefore, the use of therapeutic agents that block chemokine activity might be useful in treating chronic Lyme arthritis.