Chemokines constitute a rapidly growing family of low molecular weight proteins, characterized by the conservation of four cysteines, which are important for their tertiary structure [1]. Disulfide bridges are formed between cysteines one and three and between cysteines two and four. Chemokines have been classified into two major subfamilies, namely CXC and CC chemokines, depending on whether their first two NH 2-terminal cysteines are separated by an amino acid (CXC) or are adjacent (CC)[1]. The CXC chemokine subfamily can be further divided into ELR+ and ELR-CXC chemokines, based on the presence or absence of the Glu-Leu-Arg (ELR) motif, just in front of the first cysteine. ELR+ CXC chemokines are angiogenic and mainly attract neutrophils, whereas ELR-CXC chemokines have angiostatic properties and preferentially attract monocytes and lymphocytes. In contrast, CC chemokines are chemotactic for a variety of leukocyte subsets. In addition to the 15 CXC chemokines and 27 CC chemokines already identified, two other chemokines, fractalkine and lymphotactin (alpha and beta), have also been characterized [1]. Lymphotactin lacks cysteines one and three of the typical chemokine structure and is, so far, the only member of the C chemokine subfamily. It exerts chemotactic activity on T lymphocytes and natural killer (NK) cells. Fractalkine, on the other hand, belongs to the CX 3 C chemokine subfamily as it exhibits three amino acids between the first two cysteines. It is the only membrane-bound chemokine and chemoattracts T lymphocytes as well as monocytes. In contrast to tumor cells, which often constitutively produce chemokines, normal cells are generally poor chemokine producers, unless they are stimulated with an appropriate endogeneous (cytokine) or exogeneous (plant, viral, or bacterial products) inducer. Instead of remaining in solution, in vivo, chemokines are immobilized through low affinity binding to extracellular matrix proteins or to proteoglycans on the endothelium. This provides a mechanism for gradient formation under conditions of high blood flow and, in addition, facilitates the interactions of chemokines with passing leukocytes. Chemokines exert their activities on target cells through high affinity binding to and signaling through G protein-coupled receptors (GPCR) belonging to the serpentine receptor family [2]. So far, five CXC chemokine receptors (CXCR1-5), ten CC chemokine receptors (CCR1-10), one C chemokine receptor (XCR1) and one CX 3 C chemokine receptor (CX 3 CR1) have been characterized [2]. Recently, some chemokine receptors were found to function as a coreceptor for entry of HIV-1 (human immunodeficiency virus-1) into macrophages or T-lymphocytes. In the absence of this coreceptor, HIV-1 can bind to its target cell (via the primary receptor CD4), but the fusion process cannot take place. Macrophage (M)-tropic (R5) HIV-1 strains, which are able to infect macrophages and primary T cells, but not T cell lines, use CCR5 as a coreceptor, whereas T cell-tropic (X4) HIV-1 strains that can only grow in primary T cells and T cell lines, require CXCR4 for entry [1, 2]. The CC chemokine" monocyte chemotactic protein-3"(MCP-3) binds to CCR5 and is therefore a potential inhibitor of R5 HIV-1 infection. In addition, it is the most pluripotent chemokine, attracting monocytes, lymphocytes, granulocytes, NK cells and dendritic cells [1].