LFA-1 integrin redistribution during T-cell hybridoma invasion of hepatocyte cultures and manganese-induced adhesion to ICAM-1

Metalloimmunology: The metal ion-controlled immunity

Metals are essential components in all forms of life required for the function of nearly half of all enzymes and are critically involved in virtually all fundamental biological processes. Especially, the transition metals iron (Fe), zinc (Zn), manganese (Mn), nickel (Ni), copper (Cu) and cobalt (Co) are crucial micronutrients known to play vital roles in metabolism as well due to their unique redox properties. Metals carry out three major functions within metalloproteins: to provide structural support, to serve as enzymatic cofactors, and to mediate electron transportation. Metal ions are also involved in the immune system from metal allergies to nutritional immunity. Within the past decade, much attention has been drawn to the roles of metal ions in the immune system, since increasing evidence has mounted to suggest that metals are critically implicated in regulating both the innate immune sensing of and the host defense against invading pathogens. The importance of ions in immunity is also evidenced by the identification of various immunodeficiencies in patients with mutations in ion channels and transporters. In addition, cancer immunotherapy has recently been conclusively demonstrated to be effective and important for future tumor treatment, although only a small percentage of cancer patients respond to immunotherapy because of inadequate immune activation. Importantly, metal ion-activated immunotherapy is becoming an effective and potential way in tumor therapy for better clinical application. Nevertheless, we are still in a primary stage of discovering the diverse immunological functions of ions and mechanistically understanding the roles of these ions in immune regulation. This review summarizes recent advances in the understanding of metal-controlled immunity. Particular emphasis is put on the mechanisms of innate immune stimulation and T cell activation by the essential metal ions like calcium (Ca²⁺), zinc (Zn²⁺), manganese (Mn²⁺), iron (Fe²⁺/Fe³⁺), and potassium (K⁺), followed by a few unessential metals, in order to draw a general diagram of metalloimmunology.

Apicobasal polarity controls lymphocyte adhesion to hepatic epithelial cells

Loss of apicobasal polarity is a hallmark of epithelial pathologies. Leukocyte infiltration and crosstalk with dysfunctional epithelial barriers are crucial for the inflammatory response. Here, we show that apicobasal architecture regulates the adhesion between hepatic epithelial cells and lymphocytes. Polarized hepatocytes and epithelium from bile ducts segregate the intercellular adhesion molecule 1 (ICAM-1) adhesion receptor onto their apical, microvilli-rich membranes, which are less accessible by circulating immune cells. Upon cell depolarization, hepatic ICAM-1 becomes exposed and increases lymphocyte binding. Polarized hepatic cells prevent ICAM-1 exposure to lymphocytes by redirecting basolateral ICAM-1 to apical domains. Loss of ICAM-1 polarity occurs in human inflammatory liver diseases and can be induced by the inflammatory cytokine tumor necrosis factor alpha (TNF-α). We propose that adhesion receptor polarization is a parenchymal immune checkpoint that allows functional epithelium to hamper leukocyte binding. This contributes to the haptotactic guidance of leukocytes toward neighboring damaged or chronically inflamed epithelial cells that expose their adhesion machinery.

From rolling to arrest on blood vessels: leukocyte tap dancing on endothelial integrin ligands and chemokines at sub-second contacts

In order to extravasate the bloodstream at specific sites of inflammation or antigen presentation, circulating leukocytes must rapidly translate specific adhesive and stimulatory signals into firm adhesion. Leukocyte arrest is nearly exclusively mediated by integrin receptors. Recent in vitro and in vivo evidence suggests that specialized integrins support reversible tethers that slow down selectin-initiated rolling of leukocytes prior to their arrest. In situ activation of integrin avidity by ligand and chemokine signaling can take place within fractions of seconds, resulting either in augmented reversible adhesions or immediate arrest on the vascular endothelium. The ability of leukocyte integrins to rapidly respond to these in situ avidity modulators appears to depend on preformed affinity and clustering states, which are internally regulated by cytoskeletal constraints on integrin conformation and mobility. We discuss potential regulatory mechanisms by which a given set of chemokine receptors and integrins may interact to rapidly generate high avidity, shear-resistant integrin-mediated leukocyte arrest on vascular endothelium.

Stromal cell-derived factor-1-induced LFA-1 activation during in vivo migration of T cell hybridoma cells requires Gq/11, RhoA, and myosin, as well as Gi and Cdc42

Dissemination of T cell hybridomas in mice, a model for in vivo migration of memory T cells and for T lymphoma metastasis, depends on the chemokine stromal cell-derived factor-1 (SDF-1) and the integrin LFA-1 and correlates well with invasion into fibroblast cultures. In addition to the known role of the pertussis toxin-sensitive heterotrimeric GTPase G(i), we show that also the pertussis toxin-insensitive GTPase G(q/11) is required for dissemination and invasion. Furthermore, we show that the small GTPases, Cdc42 and RhoA, are involved, and that invasion is blocked by inhibitors of actinomyosin contraction. G(q/11), RhoA, and contraction are specifically required for LFA-1 activation, since 1) they are essential for LFA-1-dependent migration toward low SDF-1 concentrations through ICAM-1-coated filters, but not for migration toward high SDF-1 levels, which is LFA-1 independent; 2) G protein (AlF(4)(-))-induced adhesion to ICAM-1 requires RhoA and contraction; 3) constitutively active G(q) induces aggregation, mediated by LFA-1. We previously reported that binding of this activated LFA-1 to ICAM-1 triggers a signal, transduced by the zeta-associated protein 70 tyrosine kinase, that activates additional LFA-1 molecules. This amplification of LFA-1 activation is essential for invasion. We show here that zeta-associated protein 70-induced LFA-1 activation requires neither Cdc42 and RhoA nor contraction and is thus quite different from that induced by SDF-1. We conclude that two modes of LFA-1 activation, with distinct underlying mechanisms, are required for the in vivo migration of T cell hybridomas.

Liver metastases are enhanced in homozygous deletionally mutant ICAM-1 or LFA-1 mice

BACKGROUND

Adhesion molecules play an integral role in tumor growth, invasion, and metastasis and have been shown to influence the immune response to malignant cells. The interaction of intercellular adhesion molecule-1 (ICAM-1) with lymphocyte function antigen-1 (LFA-1) is important for the adhesion of leukocytes, monocytes and lymphocytes to endothelial cells in vitro and in vivo. In order to explore the role of the ICAM-1/LFA-1 interaction in liver metastases, we utilized homozygous deletionally mutant (gene knockout) mice for ICAM-1 or LFA-1 which had been derived from the C57BL6/J background.

MATERIALS AND METHODS

Wild-type C57BL6/J mice were used as controls. Animals were anesthetized and underwent a 1-cm midline lower abdominal incision. The ileocolic vein was identified and B16 melanoma cells (10(4)) were injected. The incisions were closed with skin clips. Two weeks following surgery, mice were sacrificed and their livers resected for gross and histological analysis.

RESULTS

LFA-1 deficient mice developed 13 times the number of metastases compared to wild-type controls and ICAM-1 deficient mice developed 7 times that number [13.5 (n = 17) vs 1.0 (n = 19) and 36 (n = 10) vs 5.0 (n = 16), P values of 0.0003 and 0.0002 by Wilcoxon Rank Sum Test, respectively]: Histologically, multiple areas of inflammatory cells consisting of T-cells and macrophages were noted in wild-type mice. Only sparse inflammatory cells were noted surrounding the metastases in the null mice.

CONCLUSIONS

Liver metastases of the B16 melanoma are markedly enhanced in ICAM-1 null and LFA-1 null mice. The ICAM-1/LFA-1 interaction is crucial to the immune response to liver metastases.

Efficacy of anti-intercellular adhesion molecule-1 immunotherapy on immune responses to allogeneic hepatocytes in mice

Adhesion molecules appear to play important roles in vascularized organ allograft rejection, because antibodies directed against them are effective in prolonging survival of vascularized organ allografts in rodents. However, the efficacy of these agents for cellular allografts is unknown. The current studies were undertaken to determine the role of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) on host immune responses to purified hepatocytes. Host mice (C3H, H-2(k)) grafted with hepatocytes in sponge matrix allografts (HC-SMA) received IgG isotype control, anti-ICAM-1, or anti-VCAM-1 monoclonal antibody (mAb) on days 0 through 9 after grafting. Twelve to 14 days later, host cells infiltrating the HC-SMA were assessed for the development of allospecific cytolytic T cells (allo-CTLs). Treatment with anti-ICAM-1 or anti-VCAM-1 mAb resulted in significantly decreased recruitment of host cells into HC-SMA (P < .035). However, only anti-ICAM-1 mAb resulted in abrogation of development of allo-CTLs in HC-SMA (P = .001). C3H (H-2(k)) hosts grafted with allogeneic hepatocytes from control C57BL/6 (H-2(b)) or ICAM-1 knockout [H-2(b)] mice elicited the development of allo-CTLs in HC-SMA (P = not significant). Furthermore, there was no difference in the development of allo-CTLs in HC-SMA of control hosts [C57BL/6, H-2(b)] compared with ICAM-1 knockout hosts (H-2(b)) (P = not significant). Treatment with anti-ICAM-1 mAb had no effect on the development of allo-CTLs in ICAM-1 knockout (H-2(b)) hosts bearing HC-SMA. The immunosuppressive effect of host treatment with anti-ICAM-1 mAb does not appear to be a consequence of simple blockage of donor hepatocyte or host immune cell expression of ICAM-1, but suggests a potential inhibitory effect on host immune cell activation or function, as well as an effect on recruitment of host cells to the allograft.

Ligation of the beta2 integrin triggers activation and degranulation of human eosinophils

Evidence suggests that cellular adhesion is critical for eosinophil effector functions. Here, we tested the hypothesis that an adhesion molecule, specifically beta2 integrin, participates in intracellular signaling events of eosinophils. Eosinophils stimulated with interleukin (IL)-5 and adherent to protein-coated tissue culture plates via beta2 integrin (CD18) showed tyrosine phosphorylation of a number of proteins. Among these proteins, tyrosine phosphorylation of the 105 kD and 115 kD proteins and the product of the c-cbl protooncogene, Cbl, was specifically inhibited using soluble anti-CD18 monoclonal antibody (mAb) to block eosinophil cell adhesion. Furthermore, phosphoinositide turnover of IL-5-stimulated adherent eosinophils was also inhibited by anti-CD18 mAb, suggesting that cellular adhesion plays important roles in eosinophil signal transduction. alphaM beta2 (Mac-1, CD11b/18) was one of the beta2 integrins involved in eosinophil adhesion to protein-coated plates. We found that direct ligation of eosinophil alphaM beta2 with anti-CD11b mAb coupled to polystyrene microbeads induced tyrosine phosphorylation of a 115 kD protein and Cbl. Furthermore, anti-CD11b mAb microbeads induced increases in both phosphoinositide hydrolysis and the eosinophil degranulation response. Control antibodies, such as mouse myeloma IgG1 and anti-HLA class I antigen mAb, did not induce these cellular responses. These results suggest that engagement of beta2 integrin either by cell adhesion or by anti-CD11b mAb triggers activation of an intracellular signaling cascade, including protein tyrosine phosphorylation and phosphoinositide turnover, and subsequent cellular degranulation in human eosinophils. Tyrosine phosphorylation of a 115 kD protein and Cbl may play important roles in adhesion-dependent cellular functions of eosinophils.

Substance P promotes lymphocyte-endothelial cell adhesion preferentially via LFA-1/ICAM-1 interactions

Substance P (SP), an 11 amino acid peptide, is released by C and A delta sensory nerve fibers during tissue insult and inflammation. We investigated the effect of SP on the expression and avidity of adhesion molecules, on lymphocytes and endothelial cells, which are central to the inflammatory cascade. Using in vitro adhesion assays we found that pretreatment of murine endothelial cells with SP enhanced their adhesiveness to splenocytes, the murine T cell hybridoma EL4 and nylon-enriched primary murine T cells in a dose and time dependent manner, the optimum dose being 10(-10) M and the optimum time 6 h. SP at 10(-10) M was also able to stimulate the splenocytes, EL4 T cells and primary T cells to enhance their adhesiveness for endothelial cells. The increased adhesiveness was associated with enhanced expression of ICAM-1 on endothelial cells and increased avidity of LFA-1 on lymphocytes. Further SP was chemotactic for T cells. These data suggest that SP modulates lymphocyte-endothelial cell interactions by preferentially upregulating LFA-1 and ICAM-1 interactions.

Alpha L beta 2 integrin/LFA-1 binding to ICAM-1 induced by cytohesin-1, a cytoplasmic regulatory molecule

The avidity of integrin adhesion receptors for extracellular ligands is subject to dynamic regulation by intracellular programs that have yet to be elucidated. We describe here a protein, cytohesin-1, which specifically interacts with the intracellular portion of the integrin beta 2 chain (CD18). The molecule shows homology to the yeast SEC7 gene product and bears a pleckstrin homology (PH) domain. Overexpression of either the full-length cytohesin-1 or the SEC7 domain induces beta 2 integrin-dependent binding of Jurkat cells to ICAM-1, whereas expression of the isolated cytohesin-1 PH domain inhibits T cell receptor-stimulated adhesion. Similar inhibition is not exhibited by PH domains taken from other proteins, showing that the interaction is specific and that individual PH domains are capable of discriminating between alternative targets.

Ins and outs of LFA-1

Leukocyte function-associated molecule 1 (LFA-1) is an integrin that plays a major role in the immune system. Recent findings demonstrate that LFA-1 has a two-way signaling function, mediating cell adhesion and stimulating intracellular processes at the same time. Here, Marijke Lub, Yvette van Kooyk and Carl Figdor discuss the 'inside-out' and 'outside-in' signaling properties of LFA-1, as a prototype leukocyte integrin, in normal and malignant T cells. They integrate data into a model that highlights the role of the cytoskeleton in the regulation of LFA-1.