CC Chemokine Subfamily Research Articles

The human MIP-1beta chemokine is encoded by two paralogous genes, ACT-2 and LAG-1.

Human macrophage inflammatory protein-1 beta (MIP-1beta) is an Mr 8,000 acidic protein that is upregulated upon stimulation in monocytes, T cells, and other lymphocytes. This protein belongs to the CC chemokine subfamily and directs the migration of specific subsets of leukocytes. The first molecular clone was isolated in 1988, and ever since there has been confusion regarding the exact number of genes encoding this and closely related proteins. PCR primers were designed from two genomic GenBank entries to conduct single-strand conformational polymorphism analysis, sequence analysis, and PCR-RFLP, and we conclude that previously isolated clones referred to as MIP-1beta are derived from two genes, originally called ACT-2 and LAG-1. The two proteins share a common length and are identical at 89 of 92 amino acids. The first two amino acid differences, V12M and L20P, occur in the signal peptide, while the third, G70S, is in the mature protein. Within the transcribed region, the genes differ at 25 of 662 nucleotides. A survey of the NCBI expressed sequence tag database reveals that both genes are expressed in a variety of tissues, and five clones representing LAG-1 transcripts are alternatively spliced, with the 115-bp exon 2 omitted. Database searches for putative orthologues in other species revealed that the rabbit protein is about 80% similar to the two human proteins, while those of rat and mouse are 70-75% similar. Comparative sequence analysis of the human and animal proteins indicates substantially higher rates of protein evolution in the two rodents compared to human and rabbit.

Tranilast inhibits interleukin-1β-induced monocyte chemoattractant protein-1 expression in rat mesangial cells

Monocyte chemoattractant protein-1 (MCP-1), a member of the CC subfamily of chemokines, plays a crucial role in the progression of glomerulonephritis by recruitment of monocytes. Tranilast, a clinically used anti-allergic drug, has been demonstrated to have various anti-inflammatory and anti-proliferative effects, and recently has been reported to prevent restenosis after percutaneous transluminal coronary angioplasty. In this study, we investigated whether tranilast inhibits MCP-1 secretion in mesangial cells. Tranilast inhibited interleukin-1β-induced MCP-1 secretion and mRNA expression in a concentration-dependent manner. Luciferase assay showed that tranilast suppressed interleukin-1β-induced nuclear factor-κB (NF-κB)-dependent transcription. Interleukin-1β-induced Jun N-terminal kinase (JNK) activation was also suppressed selectively by tranilast. These results indicate that tranilast inhibits interleukin-1β-induced MCP-1 production, at least in part, by inhibiting NF-κB activity and that suppression of JNK activation might be involved in the inhibition of MCP-1 production. Tranilast may serve as a new therapeutic agent for glomerulonephritis through anti-chemokine property.

Neutrophils produce biologically active macrophage inflammatory protein-3α (MIP-3α) / CCL20 and MIP-3β / CCL19

Macrophage inflammatory protein-3alpha (MIP-3alpha)/CCL20 and MIP-3beta/CCL19 are members of the CC chemokine subfamily which exert their effects through specific receptors, CCR6 and CCR7, respectively. Previously, we have reported that human neutrophils have the capacity to produce a number of chemokines, including IL-8/CXCL8, GROalpha/CXCL1, IP-10/CXCL10, and MIG/CXCL9. Herein, we show that neutrophils also have the ability to express and release MIP-3alpha/CCL20 and MIP-3beta/CCL19 when cultured with either LPS or TNF-alpha. We also report that MIP-3alpha/CCL20 and MIP-3beta/CCL19 production by LPS-stimulated neutrophils is negatively modulated by IL-10. Remarkably, we found that supernatants harvested from stimulated neutrophils not only induced chemotaxis of both immature and mature dendritic cells (DC), but also triggered rapid integrin-dependent adhesion of CCR6- and CCR7-expressing lymphocytes to purified VCAM-1 and ICAM-1, respectively. Importantly, both chemotaxis and rapid integrin-dependent adhesion were dramatically suppressed by anti-MIP-3alpha/CCL20 and anti-MIP-3beta/CCL19 neutralizing antibodies, indicating that MIP-3alpha/CCL20 and MIP-3beta/CCL19 present in the supernatants were both biologically active. As these chemokines are primarily chemotactic for DC and specific lymphocyte subsets, the ability of neutrophils to produce MIP-3alpha/CCL20 and MIP-3beta/CCL19 might be significant in orchestrating the recruitment of these cell types to the inflamed sites and therefore in contributing to the regulation of the immune response.

Neutrophils produce biologically active macrophage inflammatory protein-3alpha (MIP-3alpha)/CCL20 and MIP-3beta/CCL19.

Macrophage inflammatory protein-3alpha (MIP-3alpha)/CCL20 and MIP-3beta/CCL19 are members of the CC chemokine subfamily which exert their effects through specific receptors, CCR6 and CCR7, respectively. Previously, we have reported that human neutrophils have the capacity to produce a number of chemokines, including IL-8/CXCL8, GROalpha/CXCL1, IP-10/CXCL10, and MIG/CXCL9. Herein, we show that neutrophils also have the ability to express and release MIP-3alpha/CCL20 and MIP-3beta/CCL19 when cultured with either LPS or TNF-alpha. We also report that MIP-3alpha/CCL20 and MIP-3beta/CCL19 production by LPS-stimulated neutrophils is negatively modulated by IL-10. Remarkably, we found that supernatants harvested from stimulated neutrophils not only induced chemotaxis of both immature and mature dendritic cells (DC), but also triggered rapid integrin-dependent adhesion of CCR6- and CCR7-expressing lymphocytes to purified VCAM-1 and ICAM-1, respectively. Importantly, both chemotaxis and rapid integrin-dependent adhesion were dramatically suppressed by anti-MIP-3alpha/CCL20 and anti-MIP-3beta/CCL19 neutralizing antibodies, indicating that MIP-3alpha/CCL20 and MIP-3beta/CCL19 present in the supernatants were both biologically active. As these chemokines are primarily chemotactic for DC and specific lymphocyte subsets, the ability of neutrophils to produce MIP-3alpha/CCL20 and MIP-3beta/CCL19 might be significant in orchestrating the recruitment of these cell types to the inflamed sites and therefore in contributing to the regulation of the immune response.

The CC chemokine RANTES as a potential contributor to breast cancer progression

In breast carcinoma, high levels of tumor-associated macrophages are correlated with lymph node metastases and clinical aggressiveness. Potential candidates that may support the recruitment of monocytes from the circulation into breast tumors are the members of the CC subfamily of chemokines. In the present study we evaluated the expression of the CC chemokine RANTES in sections of breast cancer patients diagnosed in different stages of disease. Our results indicate that high incidence and intensity of RANTES expression were directly correlated with a more advanced disease, suggesting that the chemokine may be involved in breast cancer progression. Analyses performed by using the T47D and MCF-7 human breast adenocarcinoma cells indicated that RANTES expression is tightly regulated by cytokines. Furthermore, the results of our study indicate that T47D-derived RANTES partially contributes to monocyte migration, and suggest that in vivo this chemokine may be involved in inducing monocyte infiltration to breast tumor sites. In the present study we further characterized the paracrine and autocrine mechanisms by which RANTES may support breast cancer progression. The results suggest that RANTES may be involved in a complex process, in which a crosstalk between infiltrating monocytes and the tumor cells may affect tumor progression.

Peptide mimics of monocyte chemoattractant protein-1 (MCP-1) with an antagonistic activity.

In this study, we attempted to analyze the peptide motifs recognized by 24822.111 and F9, monoclonal antibodies (mAbs) that inhibit the chemotactic activity of monocyte chemoattractant protein-1 (MCP-1), a member of the CC subfamily of chemokines. We isolated phage clones from a phage display library and identified six peptide motifs. One of these clones, C27, was strongly and specifically recognized by 24822.111 mAb, while another, G25, was similarly recognized by F9 mAb. Both the C27 motif and the G25 motif contain two cysteines in their sequences and have little homology to the primary amino acid sequence of MCP-1. These clones, however, bound to THP-1 cells, and the binding was competitively inhibited by MCP-1. The clones strongly inhibited the MCP-1-induced chemotaxis of human monocytes. The synthetic and intramolecularly disulfide-linked peptides of C27 and G25 (sC27 and sG25) also inhibited the chemotaxis induced by MCP-1, while their derivatives with serine in place of cysteine did not, suggesting the importance of the loop structure for the inhibition. These results suggest that sC27 and sG25 may mimic the MCP-1-binding domain to the MCP-1 receptor.

Oral and skin keratinocytes are stimulated to secrete monocyte chemoattractant protein-1 by tumour necrosis factor-alpha and interferon-gamma.

Monocyte chemoattractant protein-1 (MCP-1) is a member of the CC subfamily of chemokines. It is chemoattractant for monocytes, activated memory T cells and dendritic cells. We studied MCP-1 mRNA and protein production in cultured human oral keratinocytes (OK) and skin keratinocytes (SK). MCP-1 production was undetectable in resting keratinocytes. However, stimulation with tumour necrosis factors (TNF-alpha) or interferon-gamma (IFN-gamma) induced MCP-1 mRNA and protein synthesis in both cell types. Together, TNF-alpha and IFN-gamma acted synergistically to increase MCP-1 production. In each case MCP-1 production was greater for SK than OK. The kinetics of IFN-gamma-induced MCP-1 production were similar for both cell types, peaking around 72 h. In contrast, TNF-alpha induced a more rapid increase in MCP-1 production by SK than OK, peak production occurring after 24 and 72 h, respectively. IL-1alpha and IL-4 did not induce MCP-1 production. However, in combination with IFN-gamma, they induced a small extra increase in MCP-1 production in SK but not OK.

Cutaneous injection of human subjects with macrophage inflammatory protein-1 alpha induces significant recruitment of neutrophils and monocytes.

Macrophage inflammatory protein (MIP-1 alpha), a member of the CC chemokine subfamily, has been shown to attract T cells and monocytes in vitro and to be expressed at sites of inflammation. Although the in vitro activities of MIP-1 alpha have been well documented, the in vivo biological activities of MIP-1 alpha in humans have not been studied. To address this, we challenged human subjects by intradermal injection with up to 1000 pmol of MIP-1 alpha and performed biopsies 2, 10, and 24 h later. Although no acute cutaneous or systemic reactions were noted, endothelial cell activation, as indicated by the expression of E-selectin, was observed. In agreement with its in vitro activity, monocyte, lymphocyte, and, to a lesser degree, eosinophil infiltration was observed, peaking at 10-24 h. Surprisingly, in contrast to its reported lack of in vitro neutrophil-stimulating activity, a rapid infiltration of neutrophils was observed in vivo. This neutrophil infiltration occurred as early as 2 h, preceding the appearance of other cells, and peaked at 10 h. Interestingly, we found that neutrophils in whole blood, but not after isolation, expressed CCR1 on their cell surface. This CCR1 was thought to be functional as assessed by neutrophil CD11b up-regulation following whole-blood MIP-1 alpha stimulation. These studies substantiate the biological effects of MIP-1 alpha on monocytes and lymphocytes and uncover the previously unrecognized activity of MIP-1 alpha to induce neutrophil infiltration and endothelial cell activation, underscoring the need to evaluate chemokines in vivo in humans.

Regulated expression of MCP-1 by osteoblastic cells in vitro and in vivo.

Inflammation is characterized by the recruitment of leukocytes from the vasculature. Recent studies have implicated chemokines as an important class of mediators that function principally to stimulate leukocyte recruitment, and in some cases, leukocyte activity. There are four defined chemokine subfamilies based on their primary structure, CXC, CC, C and CX3C. Members of the CC chemokine subfamily, such as monocyte chemoattractant protein 1 (MCP-1), are chemotactic for monocytes and other leukocyte subsets. The studies described below focus on the expression of MCP-1 in vitro and in vivo in an osseous environment. These studies indicate that MCP-1 is typically not expressed in normal bone or by normal osteoblasts in vitro. Upon stimulation by inflammatory mediators, MCP-1 is up-regulated. This expression is temporally and spatially associated with the recruitment of monocytes in both osseous inflammation and during developmentally regulated bone remodelling. Furthermore, exogenous MCP-1 applied to inflamed bone enhances the recruitment of monocytes. Because monocytes produce factors that influence osseous metabolism, including but not limited to prostglandins, platelet-derived growth factor, interleukin-1 or tumor necrosis factor, chemokines that initiate their recruitment are likely to be highly important.

Virus-encoded modulators of cytokines and growth factors

Migration of leukocytes from the bone marrow to the circulation, the primary lymphoid organs and inflammatory sites is directed by chemokines and specific receptor interactions. Besides the role of this group of low molecular weight cytokines in leukocyte attraction and activation, anti-HIV and hematopoietic activities were also attributed to chemokines. On the basis of the number and arrangement of the conserved cysteines, chemokines are subdivided in two multi-member families, namely the CXC and CC chemokines, whereas fractalkine (CX3C) and lymphotactin (C) are unique relatives. The CC chemokines possess four cysteines of which the first two are adjacent. Functionally, they form a rather heterogeneous family. Here, the focus is on the monocyte chemotactic proteins and eotaxin which, on a structural basis, can be considered as a CC chemokine subfamily. Not only the protein sequences, but also the gene structures, chromosomal location, biological activities and receptor usage exhibit considerable similarities. The review is complemented with a comparison of the biological functions of the MCP/eotaxin-subfamily in physiology and pathology.

Chemokine PARC Gene (SCYA18) Generated by Fusion of Two MIP-1α/LD78α-like Genes

Two loci in the human genome, chromosomes 4q12–q21 and 17q11.2, contain clusters of CXC and CC chemokine subfamily genes, respectively. Since mice appear to contain fewer chemokine genes than humans, numerous gene duplications might have occurred in each locus of the human genome. Here we describe the genomic organization of the human pulmonary and activation-regulated CC chemokine (PARC), also known as DC-CK1 and AMAC-1. Despite high sequence similarity to a CC chemokine macrophage inflammatory protein-1α (MIP-1α)/LD78α, PARC is chemotactic for lymphocytes and not for monocytes and does not share its receptor with MIP-1α. Analyses of the BAC clones containing the humanPARCgene indicated that the gene is located most closely toMIP-1α(HGMW-approved symbolSCYA3) andMIP-1β(HGMW-approved symbolSCYA4) on chromosome 17q11.2. Dot-plot comparison suggested that thePARCgene had been generated by fusion of twoMIP-1α-like genes with deletion and selective usage of exons. Base changes accumulated before and after the fusion might have adapted the gene to a new function. Since there are variably duplicated copies of theMIP-1αgene calledLD78β(HGMW-approved symbolSCYA3L) in the vicinity of theMIP-1αgene, the locus surrounding theMIP-1αgene seems to be a “hot spring” that continuously produces new family genes. This evidence provides a new model, duplication and fusion, of the molecular basis for diversity within a gene family.

The expression of monocyte chemoattractant protein-1 and other chemokines by osteoblasts.

Chemokines are low molecular weight secretory proteins that function principally as stimulators of leukocyte recruitment. There are four defined chemokine subfamilies based on their primary structure, CXC, CC, C and CX3C. Members of the CC chemokine subfamily, a such as monocyte chemoattractant protein 1 (MCP-1) are chemotactic for monocytes and other leukocyte subsets. Because monocytes produce factors that regulate bone formation or resorption, such as PDGF, IL-1 or TNF, chemokines that initiate their recruitment are likely to be important in regulating osseous metabolism. In the studies below, data is presented demonstrating mechanisms of MCP-1 expression in osteoblastic cells. These studies establish that MCP-1 is induced during osseous inflammation and in developmentally regulated bone remodelling, and is associated with enhanced monocyte recruitment when applied to osseous lesions.

Molecular cloning of feline CC–chemokine cDNAs

cDNA clones of feline chemokines, MIP-1 α, MIP-1 β and RANTES, were molecularly isolated with the purpose of using these sequences for future investigation of the inhibitory effects on lentivirus entry and their role in immunological functions. The feline MIP-1 α and MIP-1 β cDNA clones spanned their entire coding regions encoding 93 and 92 amino acids, respectively. The amino acid sequences of feline MIP-1 α and MIP-1 β compared to those of their human, mouse and rat counterparts showed similarities of 75.3–79.6% and 73.9–88.0%, respectively. Feline MIP-1 α and MIP-1 β had four conserved cysteines with a structure made up of the first two cysteines that are characteristic of the CC–chemokine subfamily. The amino terminal of these MIP-1 α and MIP-1 β sequences was distinctly hydrophobic, suggesting that they may function as signal peptides. A partial cDNA clone consisting of 193 bp was obtained for feline RANTES, and it also showed a high degree of sequence similarity to those of other species and contained the characteristic structure made up of adjacent cysteines. These molecular clones of feline chemokines will be useful in the examination of their inhibitory effect on the cellular entry of feline immunodeficiency virus.

Effect of N-terminal truncation and solution conditions on chemokine dimer stability: nuclear magnetic resonance structural analysis of macrophage inflammatory protein 1 beta mutants.

Chemokines (chemotactic cytokines) are a family of immune system proteins, several of which have been shown to block human immunodeficiency virus (HIV) infection in various cell types. While the solved structures of most chemokines reveal protein dimers, evidence has accumulated for the biological activity of individual chemokine monomers, and a debate has arisen regarding the biological role of the chemokine dimer. Concurrent with this debate, several N-terminal truncations and modifications in the CC subfamily of chemokines have been shown to have functional significance, in many cases antagonizing their respective receptors and in some cases retaining the ability to block HIV entry to the cell. As the dimer interface of CC chemokines is located at their N-terminus, a structural study of N-terminally truncated chemokines will address the effect that this type of mutation has on the dimer-monomer equilibrium. We have studied the structural consequences of N-terminal truncation in macrophage inflammatory protein 1 beta (MIP-1 beta), a CC chemokine that has been shown to block HIV infection. Examination of nuclear magnetic resonance (NMR) spectra of a series of N-terminally truncated MIP-1 beta variants reveals that these proteins possess a range of ability to dimerize. A mutant beginning at amino acid Asp6 [termed MIP(6)] has near wild-type dimer properties, while further truncation results in weakened dimer affinity. The mutant MIP(9) (beginning with amino acid Thr9) has been found to exist solely as a folded monomer. Relaxation measurements yield a rotational correlation time of 8.6 +/- 0.1 ns for wild-type MIP-1 beta and 4.5 +/- 0.1 ns for the MIP(9) mutant, consistent with a wild-type dimer and a fully monomeric MIP(9) variant. The presence of physiological salt concentration drastically changes the monomer-dimer equilibrium for both wild-type and most mutant proteins, heavily favoring the dimeric form of the protein. These results have implications for structure-function analysis of existing chemokine mutants as well as for the larger debate regarding the biological existence and activity of the chemokine dimer.

Isolation and Characterization of LMC, a Novel Lymphocyte and Monocyte Chemoattractant Human CC Chemokine, with Myelosuppressive Activity

By searching the Expressed Sequence Tag (EST) data base, we identified a partial cDNA sequence encoding a novel human CC chemokine. The entire cDNA sequence was determined and revealed a CC chemokine whose mature protein consisted of 100 amino acids with predicted molecular weight of 11 kd. The chemokine preferantially chemoattracted lymphocytes and monocytes but not neutrophils. It was, therefore, named LMC (Lymphocyte and Monocyte Chemoattractant). LMC exhibited potent myelosuppressive activity, which was comparable to that of MIP-1α. We identified several bacterial artificial clones (BAC) containing the LMC gene along with two human CC chemokine subfamily members; leukotactin-1 (Lkn-1) and CKβ8-1/CKβ8. This data suggests that the LMC gene is located at human chromosome 17q which encompasses a human CC chemokine gene cluster.

Monocyte Chemotactic Protein-2 Activates CCR5 and Blocks CD4/CCR5-mediated HIV-1 Entry/Replication

Human immunodeficiency virus, type I (HIV-1) cell-type tropism is dictated by chemokine receptor usage: T-cell line tropic viruses use CXCR4, whereas monocyte tropic viruses primarily use CCR5 as fusion coreceptors. CC chemokines macrophage inflammatory protein (MIP)-1alpha, MIP-1beta, and RANTES (regulated on activation normal T cell expressed and secreted) inhibit CD4/CCR5-mediated HIV-1 cell fusion. MCP-2 is also a member of the CC chemokine subfamily and has the capacity to interact with at least two receptors including CCR-1 and CCR2B. In an effort to further characterize the binding properties of MCP-2 on leukocytes, we observed that MCP-2, but not MCP-1, effectively competed with MIP-1beta for binding to monocytes, suggesting that MCP-2 may interact with CCR5. As predicted, MCP-2 competitively inhibited MIP-1beta binding to HEK293 cells stably transfected with CCR5 (CCR5/293 cells). MCP-2 also bound to and induced chemotaxis of CCR5/293 cells with a potency comparable with that of MIP-1beta. Confocal microscopy indicates that MCP-2 caused remarkable and dose-dependent internalization of CCR5 in CCR5/293 cells. Furthermore, MCP-2 inhibited the entry/replication of HIV-1ADA in CCR5/293 cells coexpressing CD4. These results indicated that MCP-2 uses CCR5 as one of its functional receptors and is an additional potent natural inhibitor of HIV-1.

The T Cell-directed CC Chemokine TARC Is a Highly Specific Biological Ligand for CC Chemokine Receptor 4

Thymus and activation-regulated chemokine (TARC) is a recently identified CC chemokine that is expressed constitutively in thymus and transiently in stimulated peripheral blood mononuclear cells. TARC functions as a selective chemoattractant for T cells that express a class of receptors binding TARC with high affinity and specificity. To identify the receptor for TARC, we produced TARC as a fusion protein with secreted alkaline phosphatase (SEAP) and used it for specific binding. By stably transfecting five orphan receptors and five known CC chemokine receptors (CCR1 to -5) into K562 cells, we found that TARC-SEAP bound selectively to cells expressing CCR4. TARC-SEAP also bound to K562 cells stably expressing CCR4 with a high affinity (Kd = 0.5 nM). Only TARC and not five other CC chemokines (MCP-1 (monocyte chemoattractant protein-1), RANTES (regulated upon activation, normal T cells expressed and secreted), MIP-1alpha (macrophage inflammatory protein-1alpha), MIP-1beta, and LARC (liver and activation-regulated chemokine)) competed with TARC-SEAP for binding to CCR4. TARC but not RANTES or MIP-1alpha induced migration and calcium mobilization in 293/EBNA-1 cells stably expressing CCR4. K562 cells stably expressing CCR4 also responded to TARC in a calcium mobilization assay. Northern blot analysis revealed that CCR4 mRNA was expressed strongly in human T cell lines and peripheral blood T cells but not in B cells, natural killer cells, monocytes, or granulocytes. Taken together, TARC is a specific functional ligand for CCR4, and CCR4 is the specific receptor for TARC selectively expressed on T cells.

Regulation of Macrophage Inflammatory Protein-1α mRNA by Oxidative Stress

Accumulation of inflammatory cells within the lung has been implicated in oxidative injury. Recruitment of these cells to a tissue site is a complex process that depends in part upon the local expression of appropriate proinflammatory chemokines. Macrophage inflammatory protein-1alpha (MIP-1alpha), a member of the CC subfamily of chemokines, has been shown to contribute to monocyte/macrophage and neutrophil chemotaxis and activation. Our previous work demonstrated that MIP-1alpha mRNA expression in macrophages is induced by bacterial endotoxin. The objective of this study was to test the hypothesis that an oxidative stress alone may trigger expression of MIP-1alpha mRNA in macrophages and to determine the mechanism leading to increased expression. A rat alveolar macrophage cell line (NR8383) was exposed to H2O2 or menadione (2-methyl-1,4-naphthoquinone (MQ)), a quinone compound that undergoes redox cycling and generates reactive oxygen species continuously. Steady-state mRNA levels encoding MIP-1alpha were markedly increased (3-fold) in these cells after 1 h of exposure to 0.5 mM H2O2, remained higher than control levels after 4 h, and decreased after 6 h. Similarly, MQ (25 or 50 microM) caused a significant increase of MIP-1 alpha mRNA with a maximal induction after 4 h of exposure (5-fold). Both H2O2 and MQ-induced up-regulation of MIP-1 alpha mRNA was suppressed by co-treatment with N-acetylcysteine, a synthetic antioxidant. Co-treatment with actinomycin D reduced the MQ induction of MIP-1alpha mRNA to a greater extent than the H2O2-induced increase. Transcription of the MIP-1alpha gene was increased by exposure to both H2O2 and MQ. H2O2 treatment also induced a marked increase of the MIP-1alpha mRNA half-life, indicating post-transcriptional stabilization. These observations indicate that an oxidative stress can regulate MIP-1alpha mRNA expression by two distinct mechanisms: transcriptional activation of the MIP-1alpha gene and post-transcriptional stabilization of MIP-1alpha mRNA.

Chemokines, a family of chemotactic cytokines.

Chemokines are low-molecular-weight proteins that stimulate recruitment of leukocytes. They are secondary pro-inflammatory mediators that are induced by primary pro-inflammatory mediators such as interleukin-1 (IL-1) or tumor necrosis factor (TNF). The physiologic importance of this family of mediators is derived from their specificity. Unlike the classic leukocyte chemo-attractants, which have little specificity, members of the chemokine family induce recruitment of well-defined leukocyte subsets. Thus, chemokine expression can account for the presence of different types of leukocytes observed in various normal or pathologic states. There are two major chemokine sub-families based upon the position of cysteine residues, i.e., CXC and CC. All members of the CXC chemokine sub-family have an intervening amino acid between the first two cysteines; members of the CC chemokine sub-family have two adjacent cysteines. As a general rule (with some notable exceptions), members of the CXC chemokines are chemotactic for neutrophils, and CC chemokines are chemotactic for monocytes and a small sub-set of lymphocytes. This review discusses the potential role of chemokines in inflammation and focuses on the two best-characterized chemokines, monocyte chemoattractant protein-1 (MCP-1), a CC chemokine, and interleukin-8 (IL-8), a member of the CXC chemokine sub-family.