The CCL2 chemokine mediates monocyte egress from bone marrow and recruitment into inflamed tissues through interaction with the CCR2 chemokine receptor, and its expression is upregulated by proinflammatory cytokines. Analysis of the gene expression profile in GM-CSF– and M-CSF–polarized macrophages revealed that a high CCL2 expression characterizes macrophages generated under the influence of M-CSF, whereas CCR2 is expressed only by GM-CSF–polarized macrophages. Analysis of the factors responsible for this differential expression identified activin A as a critical factor controlling the expression of the CCL2/CCR2 pair in macrophages, as activin A increased CCR2 expression but inhibited the acquisition of CCL2 expression by M-CSF–polarized macrophages. CCL2 and CCR2 were found to determine the extent of macrophage polarization because CCL2 enhances the LPS-induced production of IL-10, whereas CCL2 blockade leads to enhanced expression of M1 polarization-associated genes and cytokines, and diminished expression of M2-associated markers in human macrophages. Along the same line, Ccr2-deficient bone marrow–derived murine macrophages displayed an M1-skewed polarization profile at the transcriptomic level and exhibited a significantly higher expression of proinflammatory cytokines (TNF-α, IL-6) in response to LPS. Therefore, the CCL2-CCR2 axis regulates macrophage polarization by influencing the expression of functionally relevant and polarization-associated genes and downmodulating proinflammatory cytokine production.

Dendritic cell-specific ICAM-3 grabbing nonintegrin (DC-SIGN) is a monocyte-derived dendritic cell (MDDC)-specific lectin which participates in dendritic cell (DC) migration and DC-T lymphocyte interactions at the initiation of immune responses and enhances trans-infection of T cells through its HIV gp120-binding ability. The generation of a DC-SIGN-specific mAb has allowed us to determine that the acquisition of DC-SIGN expression during the monocyte-DC differentiation pathway is primarily induced by IL-4, and that GM-CSF cooperates with IL-4 to generate a high level of DC-SIGN mRNA and cell surface expression on immature MDDC. IL-4 was capable of inducing DC-SIGN expression on monocytes without affecting the expression of other MDDC differentiation markers. By contrast, IFN-α, IFN-γ, and TGF-β were identified as negative regulators of DC-SIGN expression, as they prevented the IL-4-dependent induction of DC-SIGN mRNA on monocytes, and a similar inhibitory effect was exerted by dexamethasone, an inhibitor of the monocyte-MDDC differentiation pathway. The relevance of the inhibitory action of dexamethasone, IFN, and TGF-β on DC-SIGN expression was emphasized by their ability to inhibit the DC-SIGN-dependent HIV-1 binding to differentiating MDDC. These results demonstrate that DC-SIGN, considered as a MDDC differentiation marker, is a molecule specifically expressed on IL-4-treated monocytes, and whose expression is subjected to a tight regulation by numerous cytokines and growth factors. This feature might help in the development of strategies to modulate the DC-SIGN-dependent cell surface attachment of HIV for therapeutic purposes.

CCR7 is necessary to direct dendritic cells (DCs) to secondary lymphoid nodes and to elicit an adaptative immune response. Despite its importance, little is known about the molecular mechanisms used by CCR7 to direct DCs to lymph nodes. In addition to chemotaxis, CCR7 regulates the migratory speed of DCs. We investigated the intracellular pathways that regulate CCR7-dependent chemotaxis and migratory speed. We found that CCR7 induced a G_i-dependent activation of MAPK members ERK1/2, JNK, and p38, with ERK1/2 and p38 controlling JNK. MAPK members regulated chemotaxis, but not the migratory speed, of DCs. CCR7 induced activation of PI3K/Akt; however, these enzymes did not regulate either chemotaxis or the speed of DCs. CCR7 also induced activation of the GTPase Rho, the tyrosine kinase Pyk2, and inactivation of cofilin. Pyk2 activation was independent of G_i and Src and was dependent on Rho. Interference with Rho or Pyk2 inhibited cofilin inactivation and the migratory speed of DCs, but did not affect chemotaxis. Interference with Rho/Pyk2/cofilin inhibited DC migratory speed even in the absence of chemokines, suggesting that this module controls the speed of DCs and that CCR7, by activating its components, induces an increase in migratory speed. Therefore, CCR7 activates two independent signaling modules, one involving G_i and a hierarchy of MAPK family members and another involving Rho/Pyk2/cofilin, which control, respectively, chemotaxis and the migratory speed of DCs. The use of independent signaling modules to control chemotaxis and speed can contribute to regulate the chemotactic effects of CCR7.

CCR7 was described initially as a potent leukocyte chemotactic receptor that was later shown to be responsible of directing the migration of dendritic cells (DCs) to the lymph nodes where these cells play an important role in the initiation of the immune response. Recently, a variety of reports have indicated that, apart from chemotaxis, CCR7 controls the cytoarchitecture, the rate of endocytosis, the survival, the migratory speed, and the maturation of the DCs. Some of these functions of CCR7 and additional ones also have been described in other cell types. Herein we discuss how this receptor may contribute to modulate the immune response by regulating different functions in DCs. Finally, we also suggest a possible mechanism whereby CCR7 may control its multiple tasks in these cells.

The generation of pathogen-specific immune responses is dependent on the signaling capabilities of pathogen-recognition receptors. DC-SIGN is a C-type lectin that mediates capture and internalization of viral, bacterial, and fungal pathogens by myeloid dendritic cells. DC-SIGN–interacting pathogens are thought to modulate dendritic cell maturation by interfering with intracellular signaling from Toll-like receptor molecules. We report that engagement of DC-SIGN by specific antibodies does not promote dendritic cell maturation but induces ERK1/2 and Akt phosphorylation without concomitant p38MAPK activation. DC-SIGN ligation also triggers PLCγ phosphorylation and transient increases in intracellular calcium in dendritic cells. In agreement with its signaling capabilities, a fraction of DC-SIGN molecules partitions within lipid raft–enriched membrane fractions both in DC-SIGN–transfected and dendritic cells. Moreover, DC-SIGN in dendritic cells coprecipitates with the tyrosine kinases Lyn and Syk. The relevance of the DC-SIGN–initiated signals was demonstrated in monocyte-derived dendritic cells, as DC-SIGN cross-linking synergizes with TNF-α for IL-10 release and enhances the production of LPS-induced IL-10. These results demonstrate that DC-SIGN–triggered intracellular signals modulate dendritic cell maturation. Since pathogens stimulate Th2 responses via preferential activation of ERK1/2, these results provide a molecular explanation for the ability of DC-SIGN–interacting pathogens to preferentially evoke Th2-type immune responses.

Transfection of chicken vinculin cDNA into two tumor cell lines expressing diminished levels of the endogenous protein, brought about a drastic suppression of their tumorigenic ability. The SV-40-transformed Balb/c 3T3 line (SVT2) contains four times less vinculin than the parental 3T3 cells, and the rat adenocarcinoma BSp73ASML has no detectable vinculin. Restoration of vinculin in these cells, up to the levels found in 3T3 cells, resulted in an apparent increase in substrate adhesiveness, a decrease in the ability to grow in soft agar, and suppression of their capacity to develop tumors after injection into syngeneic hosts or nude mice. These results suggest that vinculin, a cytoplasmic component of cell-matrix and cell-cell adhesions, may have a major suppressive effect on the transformed phenotype.