Locomotion and chemotaxis of lymphocytes

A single-cell atlas of the aging mouse ovary

Ovarian aging leads to diminished fertility, dysregulated endocrine signaling and increased chronic disease burden. These effects begin to emerge long before follicular exhaustion. Female humans experience a sharp decline in fertility around 35 years of age, which corresponds to declines in oocyte quality. Despite a growing body of work, the field lacks a comprehensive cellular map of the transcriptomic changes in the aging mouse ovary to identify early drivers of ovarian decline. To fill this gap we performed single-cell RNA sequencing on ovarian tissue from young (3-month-old) and reproductively aged (9-month-old) mice. Our analysis revealed a doubling of immune cells in the aged ovary, with lymphocyte proportions increasing the most, which was confirmed by flow cytometry. We also found an age-related downregulation of collagenase pathways in stromal fibroblasts, which corresponds to rises in ovarian fibrosis. Follicular cells displayed stress-response, immunogenic and fibrotic signaling pathway inductions with aging. This report provides critical insights into mechanisms responsible for ovarian aging phenotypes. The data can be explored interactively via a Shiny-based web application.

IL-15 aggravates atherosclerotic lesion development in LDL receptor deficient mice

BACKGROUND

Interleukin 15 (IL-15) is a pro-inflammatory cytokine involved in inflammatory diseases and IL-15 is expressed in atherosclerotic plaques.

METHODS

To establish the role of IL-15 in atherosclerosis we studied the effect of IL-15 on atherosclerosis associated cells in vitro and in vivo by neutralizing IL-15 using a DNA vaccination strategy.

RESULTS

Upon feeding a Western type diet LDLr(-/-) mice do express higher levels of IL-15 within the spleen and the number of IL-15 expressing cells among blood leukocytes and spleen cells is increased. Addition of IL-15 to macrophages induces the expression TNF-α and CCL-2. After the mice were vaccinated against IL-15, we observe a reduction in plaque size of 75% plaque. Unexpectedly, the relative number of macrophages within the plaque was 2-fold higher in IL-15 vaccinated mice than in control mice. Vaccination against IL-15 leads to an increased cytotoxicity against IL-15 overexpressing target cells, resulting in a reduction in IL-15 expressing cells and macrophages in blood and spleen and a decreased CD4/CD8 ratio.

CONCLUSION

Hypercholesterolemia leads to upregulation of IL-15 within spleen and blood. DNA vaccination against IL-15 does markedly reduces atherosclerotic lesion size, but does not promote lesion stability.

Pathophysiological roles of chemokines in human reproduction: an overview

Chemokines are a group of small cytokines that have an ability to induce leukocyte migration. Chemokines exert their functions by binding and activating specific G protein-coupled receptors. Studies have unveiled pleiotropic bioactivities of chemokines in various phenomena ranging from immunomodulation, embryogenesis, and homeostasis to pathogenesis. In the mammalian reproductive system, chemokines unexceptionally serve in multimodal events that are closely associated with establishment, maintenance, and deterioration of fecundity. The aim of this review is to update the knowledge on chemokines in male and female genital organs, with a focus on their potential pathophysiological roles in human reproduction.

Chemotaxis Receptors and Signaling

Chemotaxis is an important cellular response common in biology. In many chemotaxing cells the signal that regulates movement is initiated by G protein-coupled receptors on the cell surface that bind specific chemoattractants. These receptors share important structural similarities with other G protein-coupled receptors, including rhodopsin, which currently serves as the best starting point for modeling their structures. However, the chemotaxis receptors also share a number of relatively unique structural features that are less common in other GPCRs. The chemoattractant ligands of chemotaxis receptors exhibit a broad variety of sizes and chemical properties, ranging from small molecules and peptides to protein ligands. As a result, different chemotaxis receptors have evolved specialized mechanisms for the early steps of ligand binding and receptor activation. The mechanism of transmembrane signaling is currently under intensive study and several alternate mechanisms proposing different conformational rearrangements of the transmembrane helices have been proposed. Some chemotaxis receptors are proposed to form dimers, and in certain cases dimer formation is proposed to play a role in transmembrane signaling. In principle the structural and dynamical changes that occur during transmembrane signaling could be specialized for different receptors, or could be broadly conserved. Extensive mutagenesis studies have been carried out, and have begun to identify critical residues involved in ligand binding, receptor activation, and transmembrane signaling.

Diverse chemotactic responses of Dictyostelium discoideum amoebae in the developing (temporal) and stationary (spatial) concentration gradients of folic acid, cAMP, Ca(2+) and Mg(2+)

The responses of Dictyostelium discoideum amoebae to developing (temporal) and stationary (spatial) gradients of folic acid, cAMP, Ca(2+), and Mg(2+) were studied using the methods of computer-aided image analysis. The results presented demonstrate that the new type of experimental chambers used for the observation of single cells moving within the investigated gradients of chemoattractants permit time lapse recording of single amoebae and determination of the trajectories of moving cells. It was found that, besides folic acid and cAMP (natural chemoattractants for Dictyostelium discoideum amoebae), also extracellular Ca(2+) and Mg(2+) are potent inducers of these cells' chemotaxis, and the amoebae of D. discoideum can respond to various chemoattractants differently. In the positively developing gradients of folic acid, cAMP, Ca(2+), and Mg(2+) oriented locomotion of amoebae directed towards the higher concentration of the tested chemoattractants was observed. However, in the negatively developing (temporal) and stationary linear (spatial) gradients, the univocal chemotaxis of amoebae was recorded only in the case of the Mg(2+) concentration gradient. This demonstrates that amoebae can respond to both developing and stationary gradients, depending upon the nature of the chemoattractant. We also investigated the effects of chosen inhibitors of signalling pathways upon chemotaxis of D. discoideum amoebae in the positively developing (temporal) gradients of tested chemoattractants. Verapamil was found to abolish the chemotaxis of amoebae only in the Ca(2+) gradients. Pertussis toxin suppressed the chemotactic response of cells in the gradients of folic acid and cAMP but did not prevent chemotaxis in those of Ca(2+) and Mg(2+), while quinacrine inhibited chemotaxis in the gradients of folic acid, cAMP, and Ca(2+) but only slightly affected chemotaxis in the Mg(2+) gradient. None of the tested inhibitors causes inhibition of cell random movement, when applied in isotropic solution. Also EDTA and EGTA up to 50 mM concentration did not inhibit locomotion of amoebae in control isotropic solutions.

Interaction between Src homology 2 domain bearing protein tyrosine phosphatase substrate-1 and CD47 mediates the adhesion of human B lymphocytes to nonactivated endothelial cells

CD47 modulates a variety of cell functions such as adhesion, spreading, and migration. Using a fusion protein consisting of the extracellular region of Src homology 2 domain bearing protein tyrosine phosphatase substrate-1 (SHPS-1) and the Fc portion of human Ig (SHPS-1-Ig) we investigated the effects of SHPS-1 as a ligand for CD47 on B lymphocytes. Although SHPS-1-Ig binding to human B cell lines was solely mediated via CD47, their binding capacity for soluble and immobilized SHPS-1-Ig varied among cell lines irrespective of the similar expression levels of CD47, suggesting that distinctive affinity/avidity states exist during B cell maturation. Nalm6 cell line and tonsilar B lymphocytes adhered to immobilized SHPS-1-Ig and showed polarization-like morphology. These effects of SHPS-1-Ig were blocked by anti-CD47 mAbs (B6H12 and SE5A5). Wortmannin, a phosphatidylinositol-3 kinase inhibitor, but not pertussis toxin significantly inhibited the polarization induced by the immobilized SHPS-1-Ig. Thus, SHPS-1 acts as an adhesive substrate via CD47 in human B lymphocyte. Immunohistochemical analyses indicated that SHPS-1 is expressed on high endothelial venule as well as macrophages in human tonsils. HUVECs also express SHPS-1 in the absence of any stimuli, and the adhesion of tonsilar B lymphocytes to nonactivated HUVECs was significantly inhibited by SE5A5, indicating that SHPS-1/CD47 interaction is involved in the adhesion. Our findings suggest that SHPS-1/CD47 interaction may contribute to the recruitment of B lymphocytes via endothelial cells under steady state conditions.

Intracellular signaling events at the leading edge of migrating cells

Cell migration is an important facet of the life cycle of immune and other cell types. A complex set of events must take place at the leading edge of motile cells before these cells can migrate. Chemokines induce the motility of various cell types by activating multiple intracellular signaling pathways. These include the activation of chemokine receptors, which are coupled to the heterotrimeric G proteins. The release of G beta gamma subunits from chemokine receptors results in the recruitment to the plasma membrane, with subsequent activation of various down-stream signaling molecules. Among these molecules are the pleckstrin homology domain-containing proteins and the phosphoinositide 3-kinase gamma which phosphorylates phospholipids and activates members of the GTP exchange factors (GEFs). These GEFs facilitate the exchange of GTP for GDP in members of GTPases. The latter are important for reorganizing the cell cytoskeleton, and in inducing chemotaxis. Chemokines also induce the mobilization of intracellular calcium from intracellular stores. Second messengers such as inositol 1,4,5 trisphosphate, and cyclic adenosine diphosphate ribose are among those induced by chemokines. In addition, the G beta gamma subunits recruit members of the G protein-coupled receptor kinases, which phosphorylate chemokine receptors, resulting in desensitization and termination of the motility signals. This review will discuss the intracellular signaling pathways induced by chemokines, particularly those activated at the leading edge of migrating cells which lead to cell polarization, cytoskeleton reorganization and motility.

Integrin-associated protein/CD47 regulates motile activity in human B-cell lines through CDC42

Cell migration requires a dynamic interaction between the cell, its substrate, and the cytoskeleton-associated motile apparatus. Integrin-associated protein (IAP)/CD47 is a 50-kd cell surface protein that is physically associated with β3 integrins and that modulates the functions of β3 integrins in various cells. However, in B-lymphocytes that express β1 integrins but few β3 integrins, the roles of IAP/CD47 remain to be determined. Cross-linking of IAP/CD47 by the immobilized anti-IAP/CD47 monoclonal antibody (mAb) B6H12, but not 2D3, produced signals to promote polarization with lamellipodia, a characteristic morphology during leukocyte migration, in pre-B and mature B-cell lines (BALL, Nalm6, ONHL-1, Daudi), but not in myeloma cell lines (RPMI8226, OPM-2). In the presence of the immobilized fibronectin (FN), soluble B6H12 could increase the rate of the polarization and activate migratory activity of BALL cells to FN in a transwell filter assay. Furthermore, the dominant-negative form of CDC42 completely blocked B6H12-induced morphologic and functional changes without inhibiting phorbol 12-myristate 13-acetate–induced spreading on FN in BALL cells, whereas the dominant-negative form of Rac1 inhibited all these changes. These findings demonstrate that in B-lymphocytes, IAP/CD47 may transduce the signals to activate the migratory activity, in which CDC42 may be specifically involved, and that IAP/CD47 shows synergistic effect with 4β1 on B-cell migration. These findings would provide new insight into the role of IAP/CD47 on B-cell function.

Integrin-associated protein/CD47 regulates motile activity in human B-cell lines through CDC42

Cell migration requires a dynamic interaction between the cell, its substrate, and the cytoskeleton-associated motile apparatus. Integrin-associated protein (IAP)/CD47 is a 50-kd cell surface protein that is physically associated with β3 integrins and that modulates the functions of β3 integrins in various cells. However, in B-lymphocytes that express β1 integrins but few β3 integrins, the roles of IAP/CD47 remain to be determined. Cross-linking of IAP/CD47 by the immobilized anti-IAP/CD47 monoclonal antibody (mAb) B6H12, but not 2D3, produced signals to promote polarization with lamellipodia, a characteristic morphology during leukocyte migration, in pre-B and mature B-cell lines (BALL, Nalm6, ONHL-1, Daudi), but not in myeloma cell lines (RPMI8226, OPM-2). In the presence of the immobilized fibronectin (FN), soluble B6H12 could increase the rate of the polarization and activate migratory activity of BALL cells to FN in a transwell filter assay. Furthermore, the dominant-negative form of CDC42 completely blocked B6H12-induced morphologic and functional changes without inhibiting phorbol 12-myristate 13-acetate–induced spreading on FN in BALL cells, whereas the dominant-negative form of Rac1 inhibited all these changes. These findings demonstrate that in B-lymphocytes, IAP/CD47 may transduce the signals to activate the migratory activity, in which CDC42 may be specifically involved, and that IAP/CD47 shows synergistic effect with 4β1 on B-cell migration. These findings would provide new insight into the role of IAP/CD47 on B-cell function.

Chemotactic activities of avian lymphocytes

Chicken lymphocytes, enriched chicken T and B lymphocytes, and a turkey B-lymphoblastoid cell line, the RP-9 cells, are used in the studies of chemotaxis in a Boyden-type chamber assay. The chemoattractants used are lipopolysaccharide, fMLP, interleukin-8, MIP1-beta, rabbit anti-chicken IgG and IgM. The results indicate that all these cells can migrate into the polycarbonate membranes in the absence of chemoattractants. When the chemoattractants are present, the numbers of migrating cells are greatly increased. It is, therefore, concluded that avian lymphocytes have the ability to migrate, and can respond to chemical signals which result in chemotaxis and accumulation of lymphocytes at the sites where the signals originate.

Recruitment of Pleckstrin and Phosphoinositide 3-Kinase γ into the Cell Membranes, and Their Association with Gβγ After Activation of NK Cells with Chemokines

The role of phosphoinositide 3 kinases (PI 3-K) in chemokine-induced NK cell chemotaxis was investigated. Pretreatment of NK cells with wortmannin inhibits the in vitro chemotaxis of NK cells induced by lymphotactin, monocyte-chemoattractant protein-1, RANTES, IFN-inducible protein-10, or stromal-derived factor-1α. Introduction of inhibitory Abs to PI 3-Kγ but not to PI 3-Kα into streptolysin O-permeabilized NK cells also inhibits chemokine-induced NK cell chemotaxis. Biochemical analysis showed that within 2–3 min of activating NK cells, pleckstrin is recruited into NK cell membranes, whereas PI 3-Kγ associates with these membranes 5 min after stimulation with RANTES. Recruited PI 3-Kγ generates phosphatidylinositol 3,4,5 trisphosphate, an activity that is inhibited upon pretreatment of NK cells with wortmannin. Further analysis showed that a ternary complex containing the βγ dimer of G protein, pleckstrin, and PI 3-Kγ is formed in NK cell membranes after activation with RANTES. The recruitment of pleckstrin and PI 3-Kγ into NK cell membranes is only partially inhibited by pertussis toxin, suggesting that the majority of these molecules form a complex with pertussis toxin-insensitive G proteins. Our results may have application for the migration of NK cells toward the sites of inflammation.

Goldman C, Waldmann TA. IL-15 Induces the Expression of Chemokines and Their Receptors in T Lymphocytes

IL-15 is a T cell growth factor that shares many biological activities with IL-2 and uses the same β/γ polypeptides of the IL-2R complex for signal transduction. Accumulating evidence implicates an important role for this cytokine in the inflammatory response of the host. Consistent with such a role, IL-15 has been shown to be a chemoattractant for T lymphocytes, NK cells, and neutrophils. Extending these observations, we now show that IL-15 is a potent inducer of CC-, CXC-, and C-type chemokines in T lymphocytes. In addition, we demonstrate that IL-15 induces CC chemokine receptors, but not CXC chemokine receptors, in a dose-dependent manner. Thus, our findings suggest that the proinflammatory effects of IL-15 at least in part may be due to the induction of chemokines and their receptors in T cells. Furthermore, we demonstrate that IL-15 promotes entry and replication of macrophage-tropic HIV in T lymphocytes and suggest a plausible mechanism by which IL-15, a cytokine that is elevated in HIV-infected individuals, may promote the transition of HIV displaying the M-tropic phenotype primarily associated with the initial transmission into the T cell-tropic phenotype that predominates as the disease progresses.

MIP-3alpha, MIP-3beta and fractalkine induce the locomotion and the mobilization of intracellular calcium, and activate the heterotrimeric G proteins in human natural killer cells

We demonstrate here that the CC chemokines macrophage inflammatory protein-3alpha (MIP-3alpha), macrophage inflammatory protein-3beta (MIP-3beta) and the CX3C chemokine fractalkine induce the chemotaxis of interleukin-2 (IL-2)-activated natural killer (IANK) cells. In addition, these chemokines enhance the binding of [gamma-35S]guanine triphosphate ([gamma-35S]GTP) to IANK cell membranes, suggesting that receptors for these chemokines are G protein-coupled. Our results show that MIP-3alpha receptors are coupled to Go, Gq and Gz, MIP-3beta receptors are coupled to Gi, Gq and Gs, whereas fractalkine receptors are coupled to Gi, and Gz. All three chemokines induced a robust calcium response flux in IANK cells. Cross-desensitization experiments show that MIP-3alpha, MIP-3beta or fractalkine use receptors not shared by each other or by the CC chemokine regulated on activation, normal, T-cell expressed, and secreted (RANTES), the CXC chemokines stromal-derived factor-1alpha (SDF-1alpha) and interferon-inducible protein-10 (IP-10), or the C chemokine lymphotactin.

Chemokines activate natural killer cells through heterotrimeric G-proteins: implications for the treatment of AIDS and cancer

Natural killer (NK) cells are anti-tumor and anti-viral effector cells. These cells show increased cytolytic activity upon stimulation with interleukin 2 or chemokines. In addition, members of the C, CC, CXC, or CX3C chemokines induce the in vitro chemotaxis of NK cells and contribute to their in vivo tissue accumulation. Chemokines induce various intracellular signaling pathways in NK cells by activating members of the heterotrimeric G-proteins. Understanding these pathways should provide an insight into NK cell activation, in vivo distribution, and tissue localization. Based on evidence showing the high lytic activity of these effector cells against transformed or virally infected cells, it is suggested that NK cells can be used to maximize the immunotherapeutic protocols for AIDS and cancer patients.