Masataka Baba

Identification and Molecular Characterization of Fractalkine Receptor CX3CR1, which Mediates Both Leukocyte Migration and Adhesion

Leukocyte trafficking at the endothelium requires both cellular adhesion molecules and chemotactic factors. Fractalkine, a novel transmembrane molecule with a CX3C-motif chemokine domain atop a mucin stalk, induces both adhesion and migration of leukocytes. Here we identify a seven-transmembrane high-affinity receptor for fractalkine and show that it mediates both the adhesive and migratory functions of fractalkine. The receptor, now termed CX3CR1, requires pertussis toxin-sensitive G protein signaling to induce migration but not to support adhesion, which also occurs without other adhesion molecules but requires the architecture of a chemokine domain atop the mucin stalk. Natural killer cells predominantly express CX3CR1 and respond to fractalkine in both migration and adhesion. Thus, fractalkine and CX3CR1 represent new types of leukocyte trafficking regulators, performing both adhesive and chemotactic functions.

Selective expression of liver and activation-regulated chemokine (LARC) in intestinal epithelium in mice and humans.

The liver and activation‐regulated chemokine (LARC), also termed MIP‐3α and Exodus, is a novel human CC chemokine with a selective chemotactic activity for lymphocytes and dendritic cells. Here we describe genomic and cDNA clones encoding the murine orthologue of LARC (mLARC). The gene consists of four exons and three introns. The 5′‐noncoding region of about 400 bp contains typical TATA and CAAT boxes but no other potential regulatory elements so far described. The cDNA encodes a CC chemokine of 97 amino acid residues with the highest homology to human LARC (64 % amino acid identity). The 3′‐noncoding region contains as many as five potential mRNA destabilization signals. mLARC was strongly and transiently induced in the murine monocytoid cell line J774 by lipopolysaccharide (LPS) but not by cytokines such as TNF‐α, IFN‐γ, IL‐1β or IL‐4. In normal mice, mLARC mRNA was expressed selectively in intestinal tissues such as small intestine and colon. Upon treatment with LPS, mLARC expression was enhanced in intestinal tissues and induced in some lymphoid tissues such as lymph nodes. Because of alternative splicing, there are two types of transcripts encoding mLARC and its variant mLARCvar with and without an N‐terminal alanine in the mature protein, respectively. Both types of transcripts appeared to be expressed in various mouse tissues. In situ hybridization revealed that epithelial cells of intestinal tissues, especially those lining lymphoid follicles, expressed mLARC. Localization of LARC mRNA in epithelial cells was also demonstrated in a human appendix. Furthermore, mLARC was efficiently chemotactic for cells such as γ δ type T cells in intestinal epithelium and naive B cells in Peyers patches. Thus, in both humans and mice, LARC may be physiologically involved in formation and function of the mucosal lymphoid tissues by attracting lymphocytes and dendritic cells toward epithelial cells.

Pivotal role of TARC, a CC chemokine, in bacteria-induced fulminant hepatic failure in mice.

Thymus and activation-regulated chemokine (TARC) is a recently identified lymphocyte-directed CC chemokine which specifically chemoattracts T helper type 2 CD4(+) T cells in human. To establish the pathophysiological roles of TARC in vivo, we investigated whether a monoclonal antibody (mAb) against TARC could inhibit the induction of hepatic lesions in murine model using Propionibacterium acnes and lipopolysaccharide (LPS). P. acnes-induced intrahepatic granuloma formation in the priming phase is essential to the subsequent liver injury elicited by a low dose of LPS. The priming phase appears to be dominated by Th1 type immune responses determined by the profile of chemokine and chemokine receptor expression. TARC was selectively produced by granuloma-forming cells, and CC chemokine receptor 4 (CCR4)-expressing CD4(+) T cells migrated into the liver after LPS administration. In vivo injection of anti-TARC mAb just before LPS administration protected the mice from acute lethal liver damage, which was accompanied by a significant reduction of both CCR4 mRNA expression and IL-4 production by liver-infiltrating CD4(+) T cells. Moreover, both TNF-alpha and Fas ligand expressions in the liver were decreased by anti-TARC treatment. These results suggest that recruitment of IL-4-producing CCR4(+) CD4(+) T cells by granuloma-derived TARC into the liver parenchyma may be a key cause of massive liver injury after systemic LPS administration.

A lymphocyte‐specific CC chemokine, secondary lymphoid tissue chemokine (SLC), is a highly efficient chemoattractant for B cells and activated T cells

Secondary lymphoid tissue chemokine (SLC) is a CC chemokine expressed mainly in lymphnodes, appendix and spleen, and specifically chemotactic for lymphocytes (Nagira et al., J. Biol. Chem. 1997. 272: 19518 – 19524). Here, we carried out transendothelial migration assays to determine the classes and subsets of lymphocytes migrating toward SLC. SLC attracted freshly isolated B cells with high efficiency and T cells modestly. Thus, SLC is the first CC chemokine with a strong chemotactic activity on fresh B cells. Among T cell types and subsets, SLC broadly attracted CD4+ and CD8+ cells, CD45RO– (naive) and CD45RO+ (memory) cells, and CD26high (activated) and CD26low/− (resting) cells. SLC also attracted both L‐selectin+ and L‐selectin– subpopulations of various T cell subsets and B cells. Furthermore, mitogenic stimulation strongly enhanced migratory responses of T cells and B cells toward SLC. By in situ hybridization, SLC mRNA was detected in the cortical parafollicular regions (the T cell areas) of a lymph node and an appendix. Collectively, SLC may be a basic chemokine supporting homeostatic migration of a broad spectrum of lymphocytes into the secondary lymphoid tissues. SLC may also be involved in immune responses by inducing highly efficient migration of T and B cells following antigenic stimulation.

Molecular cloning of a novel CC chemokine, interleukin‐11 receptor α‐locus chemokine (ILC), which is located on chromosome 9p13 and a potential homologue of a CC chemokine encoded by molluscum contagiosum virus

Molluscum contagiosum virus (MCV) encodes a CC chemokine MC148R which is likely to have been acquired from the host. By a homology search employing MC148R as a probe, we have identified a novel CC chemokine whose gene exists next to the IL‐11 receptor α (IL‐11Rα) gene in both humans and mice. Thus, this chemokine maps to chromosome 9p13 in humans where IL‐11Rα has been assigned. We term this novel chemokine IL‐11Rα‐locus chemokine (ILC). ILC has the highest homology to MC148R among the known human CC chemokines. Furthermore, ILC is strongly and selectively expressed in the skin where infection of MCV also takes place. Thus, ILC is likely to be the original chemokine of MC148R.

Constitutive expression of various chemokine genes in human T-cell lines infected with human T-cell leukemia virus type 1 : Role of the viral transactivator Tax

We examined the genetic expression of 2 CXC chemokines (IL‐8, IP‐10), 5 CC chemokines (MCP‐I, MIP‐Iα, MIP‐Iβ, RANTES, 1309) and I C chemokine (SCM‐I/lymphotactin/ATAC) in various human T‐cell lines. By Northern blot analysis, HTLV‐I‐positive T‐cell lines were found to express a number of chemokine genes at variable levels and in different combinations. However, none of the chemokine genes was expressed in HTLV‐I‐negative T‐cell lines. We further confirmed secretion of 3 chemokines (IL‐8, MIP‐Iα and RANTES) by some HTLV‐I‐positive T‐cell lines. To examine the role of the HTLV‐I‐encoded transactivator Tax in the induction of these chemokine genes, we used JPX‐9 and JPX‐M, which were stably transformed with tax and non‐functional tax, respectively, under the control of a metallothionein promoter. Induction of tax in JPX‐9 with Cd2+ was accompanied by rapid induction of IL‐8, IP‐10, MIP‐Iα, MIP‐Iβ, 1309 and SCM‐I as determined by reverse transcription PCR. No such induction was seen in JPX‐M. We thus suggest that Tax is, at least in part, responsible for constitutive expression of certain chemokine genes in HTLV‐I‐infected T cells. Aberrant production of various chemokines by HTLV‐I‐infected T cells may impact on the pathophysiology of HTLV‐I‐associated diseases.