Macrophage-derived chemokine (MDC) is a recently identified member of the CC chemokine family. MDC is not closely related to other chemokines, sharing most similarity with thymus-and activation-regulated chemokine (TARC), which contains 37% identical amino acids. Both chemokines are highly expressed in the thymus, with little expression seen in other tissues. In addition, the genes for MDC and TARC are encoded by human chromosome 16. To explore this relationship in greater detail, we have more precisely localized the MDC gene to chromosome 16q13, the same position reported for the TARC gene. We have also examined the interaction of MDC with CC chemokine receptor 4 (CCR4), recently shown to be a receptor for TARC. Using a fusion protein of MDC with secreted alkaline phosphatase, we observed high affinity binding of MDC-secreted alkaline phosphatase to CCR4-transfected L1.2 cells (K d ‫؍‬ 0.18 nM). MDC and TARC competed for binding to CCR4, while no binding competition was observed for six other chemokines (MCP-1, MCP-3, MCP-4, RANTES (regulated on activation normal T cell expressed and secreted), macrophage inflammatory protein-1␣, macrophage inflammatory protein-1␤). MDC was tested for calcium mobilization in L1.2 cells tranfected with seven different CC chemokine receptors. MDC induced a calcium flux in CCR4-transfected cells, but other receptors did not respond to MDC. TARC, which also induced calcium mobilization in CCR4 transfectants, was unable to desensitize the response to MDC. In contrast, MDC fully desensitized a subsequent response to TARC. Both MDC and TARC functioned as chemoattractants for CCR4 transfectants, confirming that MDC is also a functional ligand for CCR4. Since MDC and TARC are both expressed in the thymus, one role for these chemokines may be to attract CCR4-bearing thymocytes in the process of T cell education and differentiation.Chemokines are small secreted proteins that mediate recruitment of leukocytes to sites of inflammation (1, 2). The complexity and functions of the chemokine family have become increasingly diverse as more members have been identified and characterized. There are four subfamilies of chemokines based on the relative position of conserved cysteine residues (1, 3, 4).The largest subfamily consists of the CC chemokines, which generally induce migration of monocytes, T lymphocytes, and in some cases eosinophils, basophils, or mast cells. All chemokines mediate their activities through G protein-coupled receptors, which have a characteristic seven-transmembrane structure. These receptors are very selective and bind specific ligands with high affinity. Eight different CC chemokine receptors have been characterized to date. CCR1, 1 CCR2, CCR3, and CCR5 each has ligand specificity for at least three CC chemokines (5-12), while single high affinity ligands have been identified that recognize CCR4, CCR6, CCR7, and CCR8 (13-17).Macrophage-derived chemokine (MDC) is a novel CC chemokine synthesized by macrophages and dendritic cells (18). MDC shares only limited homology wit...

The leukocyte-restricted beta 2 (CD18) integrins mediate cell adhesion in a variety of events essential for normal immune function. Despite extensive research in this field, only three members of this integrin subfamily have been described: CD11a/CD18 (LFA-1), CD11b/CD18 (Mac-1), and CD11c/CD18 (p150,95). We have identified a cDNA encoding a fourth alpha chain, alpha d, that associates with CD18. The alpha d subunit is more closely related to CD11b and CD11c than to CD11a. This integrin is expressed at moderate levels on myelomonocytic cell lines and subsets of peripheral blood leukocytes, and more strongly on tissue-compartmentalized cells such as foam cells, specialized macrophages found in aortic fatty streaks that may develop into atherosclerotic lesions. The alpha d/CD18 molecule exhibits preferential recognition of ICAM-3 over ICAM-1.

We have identified a novel p110 isoform of phosphatidylinositol 3-kinase from human leukocytes that we have termed p110␦. In addition, we have independently isolated p110␦ from a mouse embryo library on the basis of its ability to interact with Ha-Ras V12 in the yeast two-hybrid system. This unique isoform contains all of the conserved structural features characteristic of the p110 family. Recombinant p110␦ phosphorylates phosphatidylinositol and coimmunoprecipitates with p85. However, in contrast to previously described p110 subunits, p110␦ is expressed in a tissue-restricted fashion; it is expressed at high levels in lymphocytes and lymphoid tissues and may therefore play a role in phosphatidylinositol 3-kinase-mediated signaling in the immune system. Phosphatidylinositol (PI)1 3-kinase was originally identified as an activity associated with viral oncoproteins and growth factor receptor tyrosine kinases that phosphorylates PI and its phosphorylated derivatives at the 3Ј-hydroxyl of the inositol ring (1). The purification and subsequent molecular cloning of PI 3-kinase revealed that it is a heterodimer consisting of p85 and p110 subunits (2-5).The p85 subunit acts to localize PI 3-kinase activity to the plasma membrane by virtue of the interaction of its SH2 domain with phosphorylated tyrosine residues (present in an appropriate local sequence context) in target proteins (6). Two isoforms of p85 have been identified: p85␣, which is ubiquitously expressed, and p85␤, which is primarily found in brain and lymphoid tissues (7). The p110 subunit contains the catalytic domain of PI 3-kinase, and three isoforms of p110 have thus far been reported (␣, ␤, and ␥) (3,8,9). The identification of p110␥ revealed additional complexity within this family of enzymes. p110␥ is most closely related to p110␣ and ␤ (45-48% identity in the catalytic domain) but does not make use of p85 as a targeting subunit. p110␥ contains an additional domain termed a pleckstrin homology domain near the amino terminus. The pleckstrin homology domain allows interaction with the ␤␥ subunits of heterotrimeric G proteins that appears to regulate its activity and subcellular localization (9).Additional members of this growing gene family include more distantly related lipid and protein kinases such as Vps34, TOR1, and TOR2 of Saccharomyces cerevisiae (and their mammalian homologues such as FRAP and mTOR), the human ataxia telangiectasia gene product, and the catalytic subunit of DNA-dependent protein kinase (10).The levels of phosphatidylinositol-3,4,5-triphosphate, the primary product of PI 3-kinase activation, are elevated upon treatment of cells with a wide variety of agonists (11). This observation has implicated PI 3-kinase activation in a diverse range of cellular responses including cell growth, differentiation, and apoptosis (1, 12, 13). The downstream targets of the phosphorylated lipids generated following PI 3-kinase activation have not been well characterized. However some isoforms of protein kinase C are directly activated by phosphatidyl...

Kaposi's sarcoma-associated herpesvirus (KSHV) encodes 3 genes that are homologous to cellular chemokines. vMIP-III, the product of open reading frame K4.1, is the most distantly related to human chemokines and has yet to be characterized. We have examined the interaction of vMIP-III with chemokine receptors, its expression in KS lesions, and its in ovo angiogenic properties. We show expression of vMIP-III in KS lesions and demonstrate the stimulation of angiogenesis by this chemokine, like vMIP-I and vMIP-II, in the chick chorioallantoic membrane assay. vMIP-III does not block human immunodeficiency virus entry through the coreceptors CCR3, CCR5, or CXCR4. However, vMIP-III is an agonist for the cellular chemokine receptor CCR4. CCR4 is expressed by TH2-type T cells. Consistent with this, vMIP-III preferentially chemoattracts this cell type. Because of these biologic properties and because it is expressed in KS lesions, vMIP-III may play an important role in the pathobiology of KS.