Sphk2 deletion is involved in structural abnormalities and Th17 response but does not aggravate colon inflammation induced by sub-chronic stress.

The chronic inflammatory process that characterizes inflammatory bowel diseases (IBD) is mainly driven by T-cell response to microbial and environmental antigens. Psychological stress is a potential trigger of clinical flares of IBD, and sphingosine-1-phosphate (S1P) is involved in T-cell recruitment. Hence, stress impact and the absence of sphingosine kinase 2 (Sphk2), an enzyme of S1P metabolism, were evaluated in the colon of mice after sub-chronic stress exposure. Here, we show that sub-chronic stress increased S1P in the mouse colon, possibly due to a decrease in its degradation enzymes and Sphk2. S1P accumulation could lead to inflammation and immune dysregulation reflected by upregulation of toll-like receptor 4 (TLR4) pathway, inhibition of anti-inflammatory mechanisms, cytokine-expression profile towards a T-helper lymphocyte 17 (Th17) polarization, plasmacytosis, decrease in IgA+ lymphoid lineage cells (CD45+)/B cells/plasmablasts, and increase in IgM+ B cells. Stress also enhanced intestinal permeability. Sphk2 knockout mice presented a cytokine-expression profile towards a boosted Th17 response, lower expression of claudin 3,4,7,8, and structural abnormalities in the colon. Intestinal pathophysiology should consider stress and S1P as modulators of the immune response. S1P-based drugs, including Sphk2 potentiation, represent a promising approach to treat IBD.

Arabidopsis inositol polyphosphate kinases IPK1 and ITPK1 modulate crosstalk between SA-dependent immunity and phosphate-starvation responses.

KEY MESSAGE: Selective Arabidopsis thaliana inositol phosphate kinase functions modulate response amplitudes in innate immunity by balancing signalling adjustments with phosphate homeostasis networks. Pyrophosphorylation of InsP6 generates InsP7 and/or InsP8 containing high-energy phosphoanhydride bonds that are harnessed during energy requirements of a cell. As bona fide co-factors for several phytohormone networks, InsP7/InsP8 modulate key developmental processes. With requirements in transducing jasmonic acid (JA) and phosphate-starvation responses (PSR), InsP8 exemplifies a versatile metabolite for crosstalks between different cellular pathways during diverse stress exposures. Here we show that Arabidopsis thaliana INOSITOL PENTAKISPHOSPHATE 2-KINASE 1 (IPK1), INOSITOL 1,3,4-TRISPHOSPHATE 5/6-KINASE 1 (ITPK1), and DIPHOSPHOINOSITOL PENTAKISPHOSPHATE KINASE 2 (VIH2) implicated in InsP8 biosynthesis, suppress salicylic acid (SA)-dependent immunity. In ipk1, itpk1 or vih2 mutants, constitutive activation of defenses lead to enhanced resistance against the Pseudomonas syringae pv tomato DC3000 (PstDC3000) strain. Our data reveal that upregulated SA-signaling sectors potentiate increased expression of several phosphate-starvation inducible (PSI)-genes, previously known in these mutants. In reciprocation, upregulated PSI-genes moderate expression amplitudes of defense-associated markers. We demonstrate that SA is induced in phosphate-deprived plants, however its defense-promoting functions are likely diverted to PSR-supportive roles. Overall, our investigations reveal selective InsPs as crosstalk mediators in defense-phosphate homeostasis and in reprogramming stress-appropriate response intensities.

The role of the sphingosine axis in immune regulation: A dichotomy in the anti-inflammatory effects between sphingosine kinase 1 and sphingosine kinase 2-dependent pathways.

Background: Sphingosine kinase has been identified as playing a central role in the immune cascade, being a common mediator in the cellular response to a variety of signals. The different effects of sphingosine kinase 1 and 2 (SphK1 and SphK2, respectively) activity have not been completely characterized. Aim: To determine the different roles played by SphK1 and SphK2 in the regulation of immune-mediated disorders. Methods: Nine groups of mice were studied. Concanavalin A (ConA) injection was used to induce immune-mediated hepatitis. Mice were treated with SphK1 inhibitor (termed SphK-I) and SphK2 inhibitor (termed ABC294640), prior to ConA injection, and effects of treatment on liver enzymes, subsets of T lymphocytes, and serum levels of cytokines were observed. Results: While liver enzyme elevation was ameliorated by administration of SphK1 inhibitor, SphK2 inhibitor-treated mice did not show this tendency. A marked decrease in expression of CD25+ T-cells and Foxp+ T-cells was observed in mice treated with a high dose of SphK1 inhibitor. Alleviation of liver damage was associated with a statistically significant reduction of serum IFNγ levels in mice treated with SphK1 inhibitor and not in those treated with SphK2 inhibitor. Conclusions: Early administration of SphK1 inhibitor in a murine model of immune-mediated hepatitis alleviated liver damage and inflammation with a statistically significant reduction in IFN-γ levels. The data support a dichotomy in the anti-inflammatory effects of SphK1 and SphK2, and suggests that isoenzyme-directed therapies can improve the effect of targeting these pathways.

Sphingosine kinase 2 restricts T cell immunopathology but permits viral persistence.

Chronic viral infections are often established by the exploitation of immune-regulatory mechanisms that result in nonfunctional T cell responses. Viruses that establish persistent infections remain a serious threat to human health. Sphingosine kinase 2 (SphK2) generates sphingosine 1-phosphate, which is a molecule known to regulate multiple cellular processes. However, little is known about SphK2's role during the host immune responses to viral infection. Here, we demonstrate that SphK2 functions during lymphocytic choriomeningitis virus Cl 13 (LCMV Cl 13) infection to limit T cell immune pathology, which subsequently aids in the establishment of virus-induced immunosuppression and the resultant viral persistence. The infection of Sphk2-deficient (Sphk2-/-) mice with LCMV Cl 13 led to the development of nephropathy and mortality via T cell-mediated immunopathology. Following LCMV infection, Sphk2-/- CD4+ T cells displayed increased activity and proliferation, and these cells promoted overactive LCMV Cl 13-specific CD8+ T cell responses. Notably, oral instillation of an SphK2-selective inhibitor promoted protective T cell responses and accelerated the termination of LCMV Cl 13 persistence in mice. Thus, SphK2 is indicated as an immunotherapeutic target for the control of persistent viral infections.

Effects of triptolide on the sphingosine kinase - Sphingosine-1-phosphate signaling pathway in colitis-associated colon cancer.

BACKGROUNDS: Triptolide (TP) exhibits effective activity against colon cancer in multiple preclinical models, but the mechanisms underlying the observed effects are not fully understood. Sphingosine-1-phosphate (S1P) is a potent bioactive sphingolipid involved in the regulation of colon cancer progression. The aim of this study was to investigate the effect of TP on the sphingosine kinase (SPHK)-S1P signaling pathway in colitis-associated colon cancer. METHODS: An azoxymethane (AOM)/dextran sulfate sodium (DSS) mouse model and the THP-1 cell line were used to evaluate the therapeutic effects and mechanisms of TP in colitis-associated colon cancer (CACC). Various molecular cell biology experiments, including Western blotting, real-time PCR and immunofluorescence, were used to obtain relevant experimental data. A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was also established to detect the levels of S1P in tissue and plasma. RESULTS: In the AOM/DSS mouse model, TP treatment induced a dose-dependent decrease in tumor incidence and inhibited macrophage recruitment and M2 polarization in the tumors. TP also efficiently decreased the S1P levels and SPHK1/S1PR1/S1PR2 expression and significantly inhibited activation of the S1P-mediated phosphorylation of ERK protein in macrophages. CONCLUSIONS: The results indicated that TP might influence the recruitment and polarization of tumor-associated macrophages by suppressing the SPHK-S1P signaling pathway.

Talin1 controls dendritic cell activation by regulating TLR complex assembly and signaling.

Talin critically controls integrin-dependent cell migration, but its regulatory role in skin dendritic cells (DCs) during inflammatory responses has not been investigated. Here, we show that talin1 regulates not only integrin-dependent Langerhans cell (LC) migration, but also MyD88-dependent Toll-like receptor (TLR)-stimulated DC activation. Talin1-deficient LCs failed to exit the epidermis, resulting in reduced LC migration to skin-draining lymph nodes (sdLNs) and defective skin tolerance induction, while talin1-deficient dermal DCs unexpectedly accumulated in the dermis despite their actomyosin-dependent migratory capabilities. Furthermore, talin1-deficient DCs exhibited compromised chemotaxis, NFκB activation, and proinflammatory cytokine production. Mechanistically, talin1 was required for the formation of preassembled TLR complexes in DCs at steady state via direct interaction with MyD88 and PIP5K. Local production of PIP2 by PIP5K then recruited TIRAP to the preassembled complexes, which were required for TLR signalosome assembly during DC activation. Thus, talin1 regulates MyD88-dependent TLR signaling pathways in DCs through a novel mechanism with implications for antimicrobial and inflammatory immune responses.

Discovery and Differential Processing of HLA Class II-Restricted Minor Histocompatibility Antigen LB-PIP4K2A-1S and Its Allelic Variant by Asparagine Endopeptidase.

Minor histocompatibility antigens are the main targets of donor-derived T-cells after allogeneic stem cell transplantation. Identification of these antigens and understanding their biology are a key requisite for more insight into how graft vs. leukemia effect and graft vs. host disease could be separated. We here identified four new HLA class II-restricted minor histocompatibility antigens using whole genome association scanning. For one of the new antigens, i.e., LB-PIP4K2A-1S, we measured strong T-cell recognition of the donor variant PIP4K2A-1N when pulsed as exogenous peptide, while the endogenously expressed variant in donor EBV-B cells was not recognized. We showed that lack of T-cell recognition was caused by intracellular cleavage by a protease named asparagine endopeptidase (AEP). Furthermore, microarray gene expression analysis showed that PIP4K2A and AEP are both ubiquitously expressed in a wide variety of healthy tissues, but that expression levels of AEP were lower in primary acute myeloid leukemia (AML). In line with that, we confirmed low activity of AEP in AML cells and demonstrated that HLA-DRB1*03:01 positive primary AML expressing LB-PIP4K2A-1S or its donor variant PIP4K2A-1N were both recognized by specific T-cells. In conclusion, LB-PIP4K2A-1S not only represents a novel minor histocompatibility antigen but also provides evidence that donor T-cells after allogeneic stem cell transplantation can target the autologous allelic variant as leukemia-associated antigen. Furthermore, it demonstrates that endopeptidases can play a role in cell type-specific intracellular processing and presentation of HLA class II-restricted antigens, which may be explored in future immunotherapy of AML.

Emerging Connections of S1P-Metabolizing Enzymes with Host Defense and Immunity During Virus Infections.

The sphingosine 1-phosphate (S1P) metabolic pathway is a dynamic regulator of multiple cellular and disease processes. Identification of the immune regulatory role of the sphingosine analog FTY720 led to the development of the first oral therapy for the treatment of an autoimmune disease, multiple sclerosis. Furthermore, inhibitors of sphingosine kinase (SphK), which mediate S1P synthesis, are being evaluated as a therapeutic option for the treatment of cancer. In conjunction with these captivating discoveries, S1P and S1P-metabolizing enzymes have been revealed to display vital functions during virus infections. For example, S1P lyase, which is known for metabolizing S1P, inhibits influenza virus replication by promoting antiviral type I interferon innate immune responses. In addition, both isoforms of sphingosine kinase have been shown to regulate the replication or pathogenicity of many viruses. Pro- or antiviral activities of S1P-metabolizing enzymes appear to be dependent on diverse virus-host interactions and viral pathogenesis. This review places an emphasis on summarizing the functions of S1P-metabolizing enzymes during virus infections and discusses the opportunities for designing pioneering antiviral drugs by targeting these host enzymes.

Acylglycerol Kinase Maintains Metabolic State and Immune Responses of CD8+ T Cells.

CD8+ T cell expansions and functions rely on glycolysis, but the mechanisms underlying CD8+ T cell glycolytic metabolism remain elusive. Here, we show that acylglycerol kinase (AGK) is required for the establishment and maintenance of CD8+ T cell metabolic and functional fitness. AGK deficiency dampens CD8+ T cell antitumor functions in vivo and perturbs CD8+ T cell proliferation in vitro. Activation of phosphatidylinositol-3-OH kinase (PI3K)-mammalian target of rapamycin (mTOR) signaling, which mediates elevated CD8+ T cell glycolysis, is tightly dependent on AGK kinase activity. Mechanistically, T cell antigen receptor (TCR)- and CD28-stimulated recruitment of PTEN to the plasma membrane facilitates AGK-PTEN interaction and AGK-triggered PTEN phosphorylation, thereby restricting PTEN phosphatase activity in CD8+ T cells. Collectively, these results demonstrate that AGK maintains CD8+ T cell metabolic and functional state by restraining PTEN activity and highlight a critical role for AGK in CD8+ T cell metabolic programming and effector function.

Sphingosine kinase 2 is a negative regulator of inflammatory macrophage activation.

Sphingosine kinases (SPHK) generate the sphingolipid sphingosine-1-phosphate, which, among other functions, is a potent regulator of inflammation. While SPHK1 produces S1P to promote inflammatory signaling, the role of SPHK2 is unclear due to divergent findings in studies utilizing gene depletion versus inhibition of catalytic activity. We sought to clarify how SPHK2 affects inflammatory signaling in human macrophages, which are main regulators of inflammation. SPHK2 expression and activity were rapidly decreased within 6 h upon stimulating primary human macrophages with lipopolysaccharide (LPS), but was upregulated after 24 h. At 24 h following LPS stimulation, targeting SPHK2 with the inhibitor ABC294640, a specific siRNA or by using Sphk2-/- mouse peritoneal macrophages increased inflammatory cytokine production. Downregulation of SPHK2 in primary human macrophages within 6 h of LPS treatment was blocked by inhibiting autophagy. SPHK2 overexpression or inhibiting autophagy 6 h after human macrophage activation with LPS suppressed inflammatory cytokine release. Mechanistically, SPHK2 suppressed LPS-triggered NF-κB activation independent of its catalytic activity and prevented increased mitochondrial ROS formation downstream of LPS. In conclusion, SPHK2 is an anti-inflammatory protein in human macrophages that is inversely coupled to inflammatory cytokine production. This needs consideration when targeting SPHK2 with specific inhibitors.

From APOBEC to ZAP: Diverse mechanisms used by cellular restriction factors to inhibit virus infections.

Antiviral restriction factors are cellular proteins that inhibit the entry, replication, or spread of viruses. These proteins are critical components of the innate immune system and function to limit the severity and host range of virus infections. Here we review the current knowledge on the mechanisms of action of several restriction factors that affect multiple viruses at distinct stages of their life cycles. For example, APOBEC3G deaminates cytosines to hypermutate reverse transcribed viral DNA; IFITM3 alters membranes to inhibit virus membrane fusion; MXA/B oligomerize on viral protein complexes to inhibit virus replication; SAMHD1 decreases dNTP intracellular concentrations to prevent reverse transcription of retrovirus genomes; tetherin prevents release of budding virions from cells; Viperin catalyzes formation of a nucleoside analogue that inhibits viral RNA polymerases; and ZAP binds virus RNAs to target them for degradation. We also discuss countermeasures employed by specific viruses against these restriction factors, and mention secondary functions of several of these factors in modulating immune responses. These important examples highlight the diverse strategies cells have evolved to combat virus infections.

A virus-packageable CRISPR screen identifies host factors mediating interferon inhibition of HIV.

Interferon (IFN) inhibits HIV replication by inducing antiviral effectors. To comprehensively identify IFN-induced HIV restriction factors, we assembled a CRISPR sgRNA library of Interferon Stimulated Genes (ISGs) into a modified lentiviral vector that allows for packaging of sgRNA-encoding genomes in trans into budding HIV-1 particles. We observed that knockout of Zinc Antiviral Protein (ZAP) improved the performance of the screen due to ZAP-mediated inhibition of the vector. A small panel of IFN-induced HIV restriction factors, including MxB, IFITM1, Tetherin/BST2 and TRIM5alpha together explain the inhibitory effects of IFN on the CXCR4-tropic HIV-1 strain, HIV-1LAI, in THP-1 cells. A second screen with a CCR5-tropic primary strain, HIV-1Q23.BG505, described an overlapping, but non-identical, panel of restriction factors. Further, this screen also identifies HIV dependency factors. The ability of IFN-induced restriction factors to inhibit HIV strains to replicate in human cells suggests that these human restriction factors are incompletely antagonized. Editorial note: This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (see decision letter).

Sphingosine Kinases promote IL-17 expression in human T lymphocytes.

Sphingosine 1-phosphate (S1P) has a role in many cellular processes. S1P is involved in cell growth and apoptosis, regulation of cell trafficking, production of cytokines and chemokines. The kinases SphK1 and SphK2 (SphKs) phosphorilate Sphingosine (Sph) to S1P and several phosphatases revert S1P to sphingosine, thus assuring a balanced pool that can be depleted by a Sphingosine lyase in hexadecenal compounds and aldehydes. There are evidences that SphK1 and 2 may per se control cellular processes. Here, we report that Sph kinases regulate IL-17 expression in human T cells. SphKs inhibition impairs the production of IL-17, while their overexpression up-regulates expression of the cytokine through acetylation of IL-17 promoter. SphKs were up-regulated also in PBMCs of patients affected by IL-17 related diseases. Thus, S1P/S1P kinases axis is a mechanism likely to promote IL-17 expression in human T cells, representing a possible therapeutic target in human inflammatory diseases.

Natural T-cell ligands that are created by genetic variants can be transferred between cells by extracellular vesicles.

CD4 T cells play a central role as helper cells in adaptive immunity. Presentation of exogenous antigens in MHC class II by professional antigen-presenting cells is a crucial step in induction of specific CD4 T cells in adaptive immune responses. For efficient induction of immunity against intracellular threats such as viruses or malignant transformations, antigens from HLA class II-negative infected or transformed cells need to be transferred to surrounding antigen-presenting cells to allow efficient priming of naive CD4 T cells. Here we show indirect antigen presentation for a subset of natural HLA class II ligands that are created by genetic variants and demonstrated that (neo)antigens can be transferred between cells by extracellular vesicles. Intercellular transfer by extracellular vesicles was not dependent on the T-cell epitope, but rather on characteristics of the full-length protein. This mechanism of (neo)antigen transfer from HLA class II-negative cells to surrounding antigen-presenting cells may play a crucial role in induction of anti-tumor immunity.

Fas/S1P1 crosstalk via NF-κB activation in osteoclasts controls subchondral bone remodeling in murine TMJ arthritis.

Enhanced turnover of subchondral trabecular bone is a hallmark of rheumatoid arthritis (RA) and it results from an imbalance between bone resorption and bone formation activities. To investigate the formation and activation of osteoclasts which mediate bone resorption, a Fas-deficient MRL/lpr mouse model which spontaneously develops autoimmune arthritis and exhibits decreased bone mass was studied. Various assays were performed on subchondral trabecular bone of the temporomandibular joint (TMJ) from MRL/lpr mice and MRL+/+ mice. Initially, greater osteoclast production was observed in vitro from bone marrow macrophages obtained from MRL/lpr mice due to enhanced phosphorylation of NF-κB, as well as Akt and MAPK, to receptor activator of nuclear factor-κB ligand (RANKL). Expression of sphingosine 1-phosphate receptor 1 (S1P1) was also significantly upregulated in the condylar cartilage. S1P1 was found to be required for S1P-induced migration of osteoclast precursor cells and downstream signaling via Rac1. When SN50, a synthetic NF-κB-inhibitory peptide, was applied to the MRL/lpr mice, subchondral trabecular bone loss was reduced and both production of osteoclastogenesis markers and sphingosine kinase (Sphk) 1/S1P1 signaling were reduced. Thus, the present results suggest that Fas/S1P1 signaling via activation of NF-κB in osteoclast precursor cells is a key factor in the pathogenesis of RA in the TMJ.

Sphingolipids in neutrophil function and inflammatory responses: Mechanisms and implications for intestinal immunity and inflammation in ulcerative colitis.

Bioactive sphingolipids are regulators of immune cell function and play critical roles in inflammatory conditions including ulcerative colitis. As one of the major forms of inflammatory bowel disease, ulcerative colitis pathophysiology is characterized by an aberrant intestinal inflammatory response that persists causing chronic inflammation and tissue injury. Innate immune cells play an integral role in normal intestinal homeostasis but their dysregulation is thought to contribute to the pathogenesis of ulcerative colitis. In particular, neutrophils are key effector cells and are first line defenders against invading pathogens. While the activity of neutrophils in the intestinal mucosa is required for homeostasis, regulatory mechanisms are equally important to prevent unnecessary activation. In ulcerative colitis, unregulated neutrophil inflammatory mechanisms promote tissue injury and loss of homeostasis. Aberrant neutrophil function represents an early checkpoint in the detrimental cycle of chronic intestinal inflammation; thus, dissecting the mechanisms by which these cells are regulated both before and during disease is essential for understanding the pathogenesis of ulcerative colitis. We present an analysis of the role of sphingolipids in the regulation of neutrophil function and the implication of this relationship in ulcerative colitis.

Unique behavior of Trypanosoma cruzi mevalonate kinase: A conserved glycosomal enzyme involved in host cell invasion and signaling.

Mevalonate kinase (MVK) is an essential enzyme acting in early steps of sterol isoprenoids biosynthesis, such as cholesterol in humans or ergosterol in trypanosomatids. MVK is conserved from bacteria to mammals, and localizes to glycosomes in trypanosomatids. During the course of T. cruzi MVK characterization, we found that, in addition to glycosomes, this enzyme may be secreted and modulate cell invasion. To evaluate the role of TcMVK in parasite-host cell interactions, TcMVK recombinant protein was produced and anti-TcMVK antibodies were raised in mice. TcMVK protein was detected in the supernatant of cultures of metacyclic trypomastigotes (MTs) and extracellular amastigotes (EAs) by Western blot analysis, confirming its secretion into extracellular medium. Recombinant TcMVK bound in a non-saturable dose-dependent manner to HeLa cells and positively modulated internalization of T. cruzi EAs but inhibited invasion by MTs. In HeLa cells, TcMVK induced phosphorylation of MAPK pathway components and proteins related to actin cytoskeleton modifications. We hypothesized that TcMVK is a bifunctional enzyme that in addition to playing a classical role in isoprenoid synthesis in glycosomes, it is secreted and may modulate host cell signaling required for T. cruzi invasion.

Phosphatidylinositol 4-Phosphate 5-Kinase ß Controls Recruitment of Lipid Rafts into the Immunological Synapse.

Phosphatidylinositol 4,5-biphosphate (PIP2) is critical for T lymphocyte activation serving as a substrate for the generation of second messengers and the remodeling of actin cytoskeleton necessary for the clustering of lipid rafts, TCR, and costimulatory receptors toward the T:APC interface. Spatiotemporal analysis of PIP2 synthesis in T lymphocytes suggested that distinct isoforms of the main PIP2-generating enzyme, phosphatidylinositol 4-phosphate 5-kinase (PIP5K), play a differential role on the basis of their distinct localization. In this study, we analyze the contribution of PIP5Kß to T cell activation and show that CD28 induces the recruitment of PIP5Kß to the immunological synapse, where it regulates filamin A and lipid raft accumulation, as well as T cell activation, in a nonredundant manner. Finally, we found that Vav1 and the C-terminal 83 aa of PIP5Kß are pivotal for the PIP5Kß regulatory functions in response to CD28 stimulation.

Cross-Talk between Shp1 and PIPKIγ Controls Leukocyte Recruitment.

Neutrophil recruitment to the site of inflammation plays a pivotal role in host defense. However, overwhelming activation and accumulation of neutrophils in the tissue may cause tissue damage and autoimmunity due to the release of cytokines, oxidants, and proteases. Neutrophil adhesion in acute inflammation is initiated by activation of αLß2 (LFA-1), which can be induced by rolling on E-selectin (slowly) or by exposure to the chemokine CXCL1 (rapidly). Despite the clinical importance, cell-intrinsic molecular mechanisms of negative regulation of integrin adhesiveness and neutrophil recruitment are poorly understood. Mice deficient in the tyrosine phosphatase Src homology 2 domain-containing protein tyrosine phosphatase 1 (Shp1) show increased leukocyte adhesion, but the interpretation of these data is limited by the severe global phenotype of these mice. In this study, we used mice with global and myeloid-restricted deletion of Shp1 to study neutrophil arrest, adhesion, crawling, and transendothelial migration in vitro and in vivo. Shp1 deficiency results in increased neutrophil adhesion in vivo; however, neutrophil crawling, transmigration, and chemotaxis were reduced in these mice. Mechanistically, Shp1 binds and controls PIPKIγ activity and, thereby, modulates phosphatidylinositol (4,5)-bisphosphate levels and adhesion. Thus, Shp1 is involved in the deactivation of integrins and regulation of neutrophil recruitment into inflamed tissue.