Lack of ICAM-1 on APCs during T cell priming leads to poor generation of central memory cells

The Monocytic Cell Line THP-1 as a Validated and Robust Surrogate Model for Human Dendritic Cells

We have implemented an improved, cost-effective, and highly reproducible protocol for a simple and rapid differentiation of the human leukemia monocytic cell line THP-1 into surrogates for immature dendritic cells (iDCs) or mature dendritic cells (mDCs). The successful differentiation of THP-1 cells into iDCs was determined by high numbers of cells expressing the DC activation markers CD54 (88%) and CD86 (61%), and the absence of the maturation marker CD83. The THP-1-derived mDCs are characterized by high numbers of cells expressing CD54 (99%), CD86 (73%), and the phagocytosis marker CD11b (49%) and, in contrast to THP-1-derived iDCs, CD83 (35%) and the migration marker CXCR4 (70%). Treatment of iDCs with sensitizers, such as NiSO4 and DNCB, led to high expression of CD54 (97%/98%; GMFI, 3.0/3.2-fold induction) and CD86 (64%/96%; GMFI, 4.3/3.2-fold induction) compared to undifferentiated sensitizer-treated THP-1 (CD54, 98%/98%; CD86, 55%/96%). Thus, our iDCs are highly suitable for toxicological studies identifying potential sensitizing or inflammatory compounds. Furthermore, the expression of CD11b, CD83, and CXCR4 on our iDC and mDC surrogates could allow studies investigating the molecular mechanisms of dendritic cell maturation, phagocytosis, migration, and their use as therapeutic targets in various disorders, such as sensitization, inflammation, and cancer.

Targeting the tissue-complosome for curbing inflammatory disease

Hyperactivated local tissue is a cardinal feature of immune-mediated inflammatory diseases of various organs such as the joints, the gut, the skin, or the lungs. Tissue-resident structural and stromal cells, which get primed during repeated or long-lasting bouts of inflammation form the basis of this sensitization of the tissue. During priming, cells change their metabolism to make them fit for the heightened energy demands that occur during persistent inflammation. Epigenetic changes and, curiously, an activation of intracellularly expressed parts of the complement system drive this metabolic invigoration and enable tissue-resident cells and infiltrating immune cells to employ an arsenal of inflammatory functions, including activation of inflammasomes. Here we provide a current overview on complement activation and inflammatory transformation in tissue-occupying cells, focusing on fibroblasts during arthritis, and illustrate ways how therapeutics directed at complement C3 could potentially target the complosome to unprime cells in the tissue and induce long-lasting abatement of inflammation.

Identification of WP1066, an inhibitor of JAK2 and STAT3, as a KV 1.3 potassium channel blocker

BACKGROUND AND PURPOSE

K_V 1.3 potassium channels play a predominant role in regulating calcium signalling that is essential for the activation and proliferation of effector memory T (T_EM ) cells. This ion channel has been recognized as a promising therapeutic target against various autoimmune diseases.

EXPERIMENTAL APPROACH

In a high-throughput screening programme, WP1066 was identified as a K_V 1.3 channel inhibitor. Using molecular biology and electrophysiological methods, the mechanism(s) underlying WP1066 blockade of Kv1.3 channels was investigated. Using T_EM cell proliferation assay and mouse delayed-type hypersensitivity (DTH) model, the effects of WP1066 were examined.

KEY RESULTS

WP1066 blocked K_V 1.3 channels in a dose-dependent manner with an IC₅₀ of 3.2 μM and induced a hyperpolarizing shift of the steady-state inactivation curve. This blockade was use-dependent, as WP1066 interacted preferentially with channels in their open state, rather than the closed state or inactivated state. When the residues located in the S6 domain scaffolding the inner vestibule, were sequentially mutated, the potency of WP1066 was significantly impaired, especially by mutations A413C and I420C, indicating a higher affinity of interacting sites for WP1066. Moreover, WP1066 effectively suppressed mouse T_EM cell proliferation in vitro and mouse DTH reaction in vivo.

CONCLUSIONS AND IMPLICATIONS

The results presented here have identified WP1066 as a K_V 1.3 channel blocker with an open-state-dependent property, providing fundamental evidence for the application of WP1066 in further immunomodulatory studies targeting K_V 1.3 channels.

Possible Role of CD11a in Primary Immune Thrombocytopenia Patients on Immunosuppressive Therapy

Background and Objectives

Immune thrombocytopenia (ITP) is one of the autoimmune diseases that presented by thrombocytopenia and increased risk of bleeding. Etiology of immune thrombocytopenia (ITP) is very complex. Lymphocyte function associated antigen-1 (LFA-1) plays important role in ITP. The aim of this study was evaluation of expression of CD11a on lymphocytes to explore its possible role in primary ITP patients also, regarding severity and response to immunosuppressive treatment.

Patients and Methods

This is a cross-sectional case-control study. Forty adult patients aged (18:58) years, 29 females and 11 males were enrolled as newly diagnosed primary ITP. Forty age and sex matched control subjects were randomly selected. The expression of CD11a on lymphocyte subpopulations (CD3+ T cells, CD3+CD4+ T cells and CD19+ B cells) was analyzed by flowcytometry at the start of the study and after 6 months of follow-up.

Results

The mean fluorescence intensity (MFI) of CD11a on CD3+ T and CD19+ B lymphocytes was significantly highly increased in ITP patients compared to healthy controls while MFI of CD11a on CD3+ CD4+Tclls was non-significant. MFI of CD11a on CD3+ and CD19+ B lymphocytes showed non-significant elevation with platelet count or bleeding score. MFI of CD11a on CD3+ showed significant highly increased level in refractory ITP compared with responder cases.

Conclusion

CD11a had possible role in the pathogenesis of ITP. Immunosuppressive therapy in ITP did not affect the level of CD11a expression on T and B lymphocytes. Levels of CD11a do not reflect the severity of ITP neither platelet count nor bleeding score. Increased MFI of CD11a in CD3+T lymphocytes of ITP patients may cause resistance to immunosuppressive therapy.

A committed tissue-resident memory T cell precursor within the circulating CD8+ effector T cell pool

An increasing body of evidence emphasizes the role of tissue-resident memory T cells (T_RM) in the defense against recurring pathogens and malignant neoplasms. However, little is known with regard to the origin of these cells and their kinship to other CD8⁺ T cell compartments. To address this issue, we followed the antigen-specific progeny of individual naive CD8⁺ T cells to the T effector (T_EFF), T circulating memory (T_CIRCM), and T_RM pools by lineage-tracing and single-cell transcriptome analysis. We demonstrate that a subset of T cell clones possesses a heightened capacity to form T_RM, and that enriched expression of T_RM–fate-associated genes is already apparent in the circulating T_EFF offspring of such clones. In addition, we demonstrate that the capacity to generate T_RM is permanently imprinted at the clonal level, before skin entry. Collectively, these data provide compelling evidence for early stage T_RM fate decisions and the existence of committed T_RM precursor cells in the circulatory T_EFF compartment.

Complement Has Brains-Do Intracellular Complement and Immunometabolism Cooperate in Tissue Homeostasis and Behavior?

The classical liver-derived and serum-effective complement system is well appreciated as a key mediator of host protection via instruction of innate and adaptive immunity. However, recent studies have discovered an intracellularly active complement system, the complosome, which has emerged as a central regulator of the core metabolic pathways fueling human immune cell activity. Induction of expression of components of the complosome, particularly complement component C3, during transmigration from the circulation into peripheral tissues is a defining characteristic of monocytes and T cells in tissues. Intracellular complement activity is required to induce metabolic reprogramming of immune cells, including increased glycolytic flux and OXPHOS, which drive the production of the pro-inflammatory cytokine IFN-γ. Consequently, reduced complosome activity translates into defects in normal monocyte activation, faulty Th1 and cytotoxic T lymphocyte responses and loss of protective tissue immunity. Intriguingly, neurological research has identified an unexpected connection between the physiological presence of innate and adaptive immune cells and certain cytokines, including IFN-γ, in and around the brain and normal brain function. In this opinion piece, we will first review the current state of research regarding complement driven metabolic reprogramming in the context of immune cell tissue entry and residency. We will then discuss how published work on the role of IFN-γ and T cells in the brain support a hypothesis that an evolutionarily conserved cooperation between the complosome, cell metabolism and IFN-γ regulates organismal behavior, as well as immunity.

Diapedesis-Induced Integrin Signaling via LFA-1 Facilitates Tissue Immunity by Inducing Intrinsic Complement C3 Expression in Immune Cells

Intrinsic complement C3 activity is integral to human T helper type 1 (Th1) and cytotoxic T cell responses. Increased or decreased intracellular C3 results in autoimmunity and infections, respectively. The mechanisms regulating intracellular C3 expression remain undefined. We identified complement, including C3, as among the most significantly enriched biological pathway in tissue-occupying cells. We generated C3-reporter mice and confirmed that C3 expression was a defining feature of tissue-immune cells, including T cells and monocytes, occurred during transendothelial diapedesis, and depended on integrin lymphocyte-function-associated antigen 1 (LFA-1) signals. Immune cells from patients with leukocyte adhesion deficiency type 1 (LAD-1) had reduced C3 transcripts and diminished effector activities, which could be rescued proportionally by intracellular C3 provision. Conversely, increased C3 expression by T cells from arthritis patients correlated with disease severity. Our study defines integrins as key controllers of intracellular complement, demonstrates that perturbations in the LFA-1-C3-axis contribute to primary immunodeficiency, and identifies intracellular C3 as biomarker of severity in autoimmunity.

Stable contacts of naïve CD4 T cells with migratory dendritic cells are ICAM-1-dependent but dispensable for proliferation in vivo

It is unclear if naïve T cells require dendritic cell ICAMs to proliferate inside lymph nodes. To check if and when CD4 lymphocytes use ICAMs on migratory DCs, wild-type and ICAM-1 and 2 double knock out bone marrow-derived DCs pulsed with saturating levels of an OT-II transgene-specific ovalbumin-derived peptide were co-transferred into skin-draining lymph nodes. Intravital imaging of OT-II lymphocytes entering these lymph nodes revealed that ICAM-1 and -2 deficient migratory DCs formed fewer stable conjugates with OT-II lymphocytes but promoted normal T cell proliferation. DC ICAMs were also not required for unstable TCR-dependent lymphocyte arrests on antigen presenting migratory DCs. Thus, rare antigen-stimulated ICAM-stabilized T-DC conjugates are dispensable for CD4 lymphocyte proliferation inside lymph nodes.

LFA-1 in T Cell Migration and Differentiation

Maintenance of homeostatic immune surveillance and development of effective adaptive immune responses require precise regulation of spatial and temporal lymphocyte trafficking throughout the body to ensure pathogen clearance and memory generation. Dysregulation of lymphocyte activation and migration can lead to impaired adaptive immunity, recurrent infections, and an array of autoimmune diseases and chronic inflammation. Central to the recruitment of T cells, integrins are cell surface receptors that regulate adhesion, signal transduction, and migration. With 24 integrin pairs having been discovered to date, integrins are defined not only by the composition of the heterodimeric pair but by cell-type specific expression and their ligands. Furthermore, integrins not only facilitate adhesion but also induce intracellular signaling and have recently been uncovered as mechanosensors providing additional complexity to the signaling pathways. Among several leukocyte-specific integrins, lymphocyte function-associated antigen-1 (LFA-1 or α_Lβ₂; CD11a/CD18) is a key T cell integrin, which plays a major role in regulating T cell activation and migration. Adhesion to LFA-1's ligand, intracellular adhesion receptor 1 (ICAM-1) facilitates firm endothelium adhesion, prolonged contact with antigen-presenting cells, and binding to target cells for killing. While the downstream signaling pathways utilized by LFA-1 are vastly conserved they allow for highly disparate responses. Here, we summarize the roles of LFA-1 and ongoing studies to better understand its functions and regulation.

Integrins in T Cell Physiology

From the thymus to the peripheral lymph nodes, integrin-mediated interactions with neighbor cells and the extracellular matrix tune T cell behavior by organizing cytoskeletal remodeling and modulating receptor signaling. LFA-1 (αLβ2 integrin) and VLA-4 (α4β1 integrin) play a key role throughout the T cell lifecycle from thymocyte differentiation to lymphocyte extravasation and finally play a fundamental role in organizing immune synapse, providing an essential costimulatory signal for the T cell receptor. Apart from tuning T cell signaling, integrins also contribute to homing to specific target organs as exemplified by the importance of α4β7 in maintaining the gut immune system. However, apart from those well-characterized examples, the physiological significance of the other integrin dimers expressed by T cells is far less understood. Thus, integrin-mediated cell-to-cell and cell-to-matrix interactions during the T cell lifespan still represent an open field of research.

Reversible Transgene Expression Reduces Fratricide and Permits 4-1BB Costimulation of CAR T Cells Directed to T-cell Malignancies

T cells expressing second-generation chimeric antigen receptors (CARs) specific for CD5, a T-cell surface marker present on normal and malignant T cells, can selectively kill tumor cells. We aimed to improve this killing by substituting the CD28 costimulatory endodomain (28.z) with 4-1BB (BB.z), as 28.z CD5 CAR T cells rapidly differentiated into short-lived effector cells. In contrast, 4-1BB costimulation is known to promote development of the central memory subpopulation. Here, we found BB.z CD5 CAR T cells had impaired growth compared with 28.z CD5.CAR T cells, due to increased T-cell-T-cell fratricide. We demonstrate that TRAF signaling from the 4-1BB endodomain upregulated the intercellular adhesion molecule 1, which stabilized the fratricidal immunologic synapse between CD5 CAR T cells. As the surviving BB.z CD5 CAR T cells retained the desired central memory phenotype, we aimed to circumvent the 4-1BB-mediated toxicity using a regulated expression system that reversibly inhibits CAR expression. This system minimized CAR signaling and T-cell fratricide during in vitro expansion in the presence of a small-molecule inhibitor, and restored CAR expression and antitumor function of transduced T cells in vivo These studies reveal a mechanism by which 4-1BB costimulation impairs expansion of CD5 CAR T cells and offer a solution to mitigate this toxicity. Cancer Immunol Res; 6(1); 47-58. ©2017 AACR.

A novel intracellular pool of LFA-1 is critical for asymmetric CD8+ T cell activation and differentiation

The integrin lymphocyte function-associated antigen 1 (LFA-1; CD11a/CD18) is a key T cell adhesion receptor that mediates stable interactions with antigen-presenting cell (APC), as well as chemokine-mediated migration. Using our newly generated CD11a-mYFP knock-in mice, we discovered that naive CD8+ T cells reserve a significant intracellular pool of LFA-1 in the uropod during migration. Intracellular LFA-1 quickly translocated to the cell surface with antigenic stimulus. Importantly, the redistribution of intracellular LFA-1 at the contact with APC was maintained during cell division and led to an unequal inheritance of LFA-1 in divided T cells. The daughter CD8+ T cells with disparate LFA-1 expression showed different patterns of migration on ICAM-1, APC interactions, and tissue retention, as well as altered effector functions. In addition, we identified Rab27 as an important regulator of the intracellular LFA-1 translocation. Collectively, our data demonstrate that an intracellular pool of LFA-1 in naive CD8+ T cells plays a key role in T cell activation and differentiation.

The Role of Lymphatic Niches in T Cell Differentiation

Long-term immunity to many viral and bacterial pathogens requires CD8(+) memory T cell development, and the induction of long-lasting CD8(+) memory T cells from a naïve, undifferentiated state is a major goal of vaccine design. Formation of the memory CD8(+) T cell compartment is highly dependent on the early activation cues received by naïve CD8(+) T cells during primary infection. This review aims to highlight the cellularity of various niches within the lymph node and emphasize recent evidence suggesting that distinct types of T cell activation and differentiation occur within different immune contexts in lymphoid organs.

The dendritic cell cytoskeleton promotes T cell adhesion and activation by constraining ICAM-1 mobility

Integrity of the dendritic cell (DC) actin cytoskeleton is essential for T cell priming, but the underlying mechanisms are poorly understood. We show that the DC F-actin network regulates the lateral mobility of intracellular cell adhesion molecule 1 (ICAM-1), but not MHCII. ICAM-1 mobility and clustering are regulated by maturation-induced changes in the expression and activation of moesin and α-actinin-1, which associate with actin filaments and the ICAM-1 cytoplasmic domain. Constrained ICAM-1 mobility is important for DC function, as DCs expressing a high-mobility ICAM-1 mutant lacking the cytoplasmic domain exhibit diminished antigen-dependent conjugate formation and T cell priming. These defects are associated with inefficient induction of leukocyte functional antigen 1 (LFA-1) affinity maturation, which is consistent with a model in which constrained ICAM-1 mobility opposes forces on LFA-1 exerted by the T cell cytoskeleton, whereas ICAM-1 clustering enhances valency and further promotes ligand-dependent LFA-1 activation. Our results reveal an important new mechanism through which the DC cytoskeleton regulates receptor activation at the immunological synapse.

ICAM-1 deficiency exacerbates sarcoid-like granulomatosis induced by Propionibacterium acnes through impaired IL-10 production by regulatory T cells

Propionibacterium acnes has been implicated as one of the suggested causative antigens for sarcoidosis, a systemic granulomatous disease. By injecting heat-killed P. acnes into the dorsal skin of C57BL/6J mice on days 1, 3, 5, and 14, sarcoid-like granulomatosis was induced in skin and lungs of these mice on day 28. To clarify the role of cell adhesion molecules in cutaneous sarcoidosis, we induced sarcoid-like granulomatosis in mice deficient of intercellular adhesion molecule (ICAM)-1, L-selectin, P-selectin, or E-selectin via repeated P. acnes injection. Histopathologic analysis revealed that granuloma formation was aggravated in the skin and lungs of ICAM-1-deficient mice compared with wild-type mice. Within skin granulomas of ICAM-1-deficient mice, P. acnes immunization up-regulated mRNA expression of tumor necrosis factor-α, although it failed to induce IL-10 mRNA expression in contrast to wild-type mice. Infiltration of regulatory T cells into skin granuloma was similar between wild-type mice and ICAM-1-deficient mice. P. acnes immunization induced IL-10 production by CD4(+)CD25(+)Foxp3(+) regulatory T cells in lymph nodes of wild-type mice in vivo, which was absent in regulatory T cells of ICAM-1-deficient mice. Our results indicate that ICAM-1 is imperative for inducing regulatory T cells to produce IL-10 in vivo, which would prevent granuloma formation.

Regulation of CD4(+) T cells by pleural mesothelial cells via adhesion molecule-dependent mechanisms in tuberculous pleurisy

Background

Intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) have been demonstrated to be expressed on pleural mesothelial cells (PMCs), and to mediate leukocyte adhesion and migration; however, little is known about whether adhesion molecule-dependent mechanisms are involved in the regulation of CD4⁺ T cells by PMCs in tuberculous pleural effusion (TPE).

Methods

Expressions of ICAM-1 and VCAM-1 on PMCs, as well as expressions of CD11a and CD29, the counter-receptors for ICAM-1 and VCAM-1, respectively, expressed on CD4⁺ T cells in TPE were determined using flow cytometry. The immune regulations on adhesion, proliferation, activation, selective expansion of CD4⁺ helper T cell subgroups exerted by PMCs via adhesion molecule-dependent mechanisms were explored.

Results

Percentages of ICAM-1-positive and VCAM-1‒positive PMCs in TPE were increased compared with PMC line. Interferon-γ enhanced fluorescence intensity of ICAM-1, while IL-4 promoted VCAM-1 expression on PMCs. Percentages of CD11a^highCD4⁺ and CD29^highCD4⁺ T cells in TPE significantly increased as compared with peripheral blood. Prestimulation of PMCs with anti‒ICAM-1 or ‒VCAM-1 mAb significantly inhibited adhesion, activation, as well as effector regulatory T cell expansion induced by PMCs.

Conclusions

Our current data showed that adhesion molecule pathways on PMCs regulated adhesion and activation of CD4⁺ T cells, and selectively promoted the expansion of effector regulatory T cells.

ICAM-1-dependent homotypic aggregates regulate CD8 T cell effector function and differentiation during T cell activation

A hallmark of T cell activation in vitro and in vivo is the clustering of T cells with each other via interaction of the LFA-1 integrin with ICAM-1. The functional significance of these homotypic aggregates in regulating T cell function remains unknown. We used an APC-free in vitro activation system to demonstrate that stimulation of purified naive CD8 T cells results in enhanced expression of ICAM-1 on T cells that is sustained by the inflammatory cytokine IL-12 and associated with robust T cell aggregates. ICAM-1-deficient CD8 T cells proliferate normally but demonstrate a striking failure to aggregate. Interestingly, loss of ICAM-1 expression results in elevated levels of IFN-γ and granzyme B, as well as enhanced cytotoxicity. Similar results were obtained when anti-LFA-1 Ab was used to block the clustering of wild-type T cells. ICAM-1 ligation is not required for IFN-γ regulation, as clustering of ICAM-1-deficient CD8 T cells with wild-type T cells reduces IFN-γ expression. Analysis using a fluorescent reporter that monitors TCR signal strength indicates that T cell clustering limits T cell exposure to Ag during activation. Furthermore, T cell clustering promotes the upregulation of the CTLA-4 inhibitory receptor and the downregulation of eomesodermin, which controls effector molecule expression. Activation of ICAM-1-deficient CD8 T cells in vivo results in an enhanced percentage of KLRG-1(+) T cells indicative of short-lived effectors. These results suggest that T cell clustering represents a mechanism that allows continued proliferation but regulates T cell effector function and differentiation.

CD11a regulates effector CD8 T cell differentiation and central memory development in response to infection with Listeria monocytogenes

β2 (CD18) integrins with α-chains CD11a, -b, -c, and -d are important adhesion molecules necessary for leukocyte migration and cellular interactions. CD18 deficiency leads to recurrent bacterial infections and poor wound healing due to reduced migration of leukocytes to inflammatory sites. CD8 T cells also upregulate CD11a, CD11b, and CD11c upon activation. However, the role these molecules play for CD8 T cells in vivo is not known. To determine the function of individual β2 integrins, we examined CD8 T cell responses to Listeria monocytogenes infection in CD11a-, CD11b-, and CD11c-deficient mice. The absence of CD11b or CD11c had no effect on the generation of antigen-specific CD8 T cells. In contrast, the magnitude of the primary CD8 T cell response in CD11a-deficient mice was significantly reduced. Moreover, the response in CD11a(-/-) mice exhibited reduced differentiation of short-lived effector cells (KLRG1(hi) CD127(lo)), although cytokine and granzyme B production levels were unaffected. Notably, CD11a deficiency resulted in greatly enhanced generation of CD62L(+) central memory cells. Surprisingly, CD8 T cells lacking CD11a mounted a robust secondary response to infection. Taken together, these findings demonstrated that CD11a expression contributes to expansion and differentiation of primary CD8 T cells but may be dispensable for secondary responses to infection.

ICAM-1-dependent tuning of memory CD8 T-cell responses following acute infection

CD8 T-cell responses are critical for protection against intracellular pathogens and tumors. The induction and properties of these responses are governed by a series of integrated processes that rely heavily on cell-cell interactions. Intercellular adhesion molecule (ICAM)-1 functions to enhance the strength of antigenic stimulation, extend the duration of contact with antigen-presenting cells, and augment cytokine signals, which are all factors that influence peripheral CD8 T-cell differentiation. Although previous studies suggest that ICAM-1 is essential for establishing memory T-cell populations following peptide immunization, the roles of ICAM-1 in antiviral cellular immunity are less well understood. Here we show that, following a prototypic acute viral infection, the formation and maintenance of memory-phenotype CD127(hi), KLRG-1(lo) CD8 T cells does not require ICAM-1. Nevertheless, ICAM-1 expression on nonlymphocytes dictates the phenotypic and functional attributes of the antiviral CD8 T-cell populations that develop and promotes the gradual attrition of residual effector-like CD127(lo), KLRG-1(hi) CD8 T cells during the memory phase of the response. Although memory T cells do emerge and are maintained if ICAM-1 expression is abolished, the secondary proliferative capacity of these T cells is severely curtailed. Collectively, these studies reveal potential dual roles for ICAM-1 in both promoting the decay of effector responses and programming the sensitivity of memory CD8 T cells to secondary stimuli.

DOCK8 is essential for T-cell survival and the maintenance of CD8+ T-cell memory

Deficiency in the guanine nucleotide exchange factor dedicator of cytokinesis 8 (DOCK8) causes a human immunodeficiency syndrome associated with recurrent sinopulmonary and viral infections. We have recently identified a DOCK8-deficient mouse strain, carrying an ethylnitrosourea-induced splice-site mutation that shows a failure to mature a humoral immune response due to the loss of germinal centre B cells. In this study, we turned to T-cell immunity to investigate further the human immunodeficiency syndrome and its association with decreased peripheral CD4(+) and CD8(+) T cells. Characterisation of the DOCK8-deficient mouse revealed T-cell lymphopenia, with increased T-cell turnover and decreased survival. Egress of mature CD4(+) thymocytes was reduced with increased migration of these cells to the chemokine CXCL12. However, despite the two-fold reduction in peripheral naïve T cells, the DOCK8-deficient mice generated a normal primary CD8(+) immune response and were able to survive acute influenza virus infection. The limiting effect of DOCK8 was in the normal survival of CD8(+) memory T cells after infection. These findings help to explain why DOCK8-deficient patients are susceptible to recurrent infections and provide new insights into how T-cell memory is sustained.

Lung effector memory and activated CD4+ T cells display enhanced proliferation in surfactant protein A-deficient mice during allergen-mediated inflammation

Although many studies have shown that pulmonary surfactant protein (SP)-A functions in innate immunity, fewer studies have addressed its role in adaptive immunity and allergic hypersensitivity. We hypothesized that SP-A modulates the phenotype and prevalence of dendritic cells (DCs) and CD4(+) T cells to inhibit Th2-associated inflammatory indices associated with allergen-induced inflammation. In an OVA model of allergic hypersensitivity, SP-A(-/-) mice had greater eosinophilia, Th2-associated cytokine levels, and IgE levels compared with wild-type counterparts. Although both OVA-exposed groups had similar proportions of CD86(+) DCs and Foxp3(+) T regulatory cells, the SP-A(-/-) mice had elevated proportions of CD4(+) activated and effector memory T cells in their lungs compared with wild-type mice. Ex vivo recall stimulation of CD4(+) T cell pools demonstrated that cells from the SP-A(-/-) OVA mice had the greatest proliferative and IL-4-producing capacity, and this capability was attenuated with exogenous SP-A treatment. Additionally, tracking proliferation in vivo demonstrated that CD4(+) activated and effector memory T cells expanded to the greatest extent in the lungs of SP-A(-/-) OVA mice. Taken together, our data suggested that SP-A influences the prevalence, types, and functions of CD4(+) T cells in the lungs during allergic inflammation and that SP deficiency modifies the severity of inflammation in allergic hypersensitivity conditions like asthma.

Human T cell microparticles circulate in blood of hepatitis patients and induce fibrolytic activation of hepatic stellate cells

Microparticles (MPs) are small cell membrane vesicles that are released from cells during apoptosis or activation. Although circulating platelet MPs have been studied in some detail, the existence and functional role of T cell MPs remain elusive. We show that blood from patients with active hepatitis C (alanine aminotransferase [ALT] level >100 IU/mL) contains elevated numbers of T cell MPs compared with patients with mild hepatitis C (ALT <40 IU/mL) and healthy controls. T cell MPs fuse with cell membranes of hepatic stellate cells (HSCs), the major effector cells for excess matrix deposition in liver fibrosis and cirrhosis. MP uptake is partly intercellular adhesion molecule 1-dependent and leads to activation of nuclear factor kappa B and extracellular signal-regulated kinases 1 and 2 and subsequent up-regulation of fibrolytic genes in HSCs, down-regulation of procollagen α1(I) messenger RNA, and blunting of profibrogenic activities of transforming growth factor β1. Ex vivo, the induced fibrolytic activity is evident in MPs derived from activated CD4+ T cells and is highest in MPs derived from activated and apoptotic CD8+ T cells. Mass spectrometry, fluorescence-activated cell sorting analysis, and function blocking antibodies revealed CD147/Emmprin as a candidate transmembrane molecule in HSC fibrolytic activation by CD8+ T cell MPs.

CONCLUSION

Circulating T cell MPs are a novel diagnostic marker for inflammatory liver diseases, and in vivo induction of T cell MPs may be a novel strategy to induce regression of liver fibrosis.

LFA-1 defect-induced effector/memory CD8+ T cell apoptosis is mediated via Bcl-2/Caspase pathways and associated with downregulation of CD27 and IL-15R

LFA-1 signaling is required for the generation of central memory CD8(+) T cells in priming phase. However, its role for effector and memory CD8(+) T cell survival in transition and maintenance phases is elusive. We transferred effector and memory CD8(+) T cells into C57BL/6 and CD54(-/-) mice, which were generated by cultivation of ovalbumin (OVA)-pulsed dendritic cells (DC(OVA)) with naïve CD8(+) T cells derived from transgenic OT I mice and purified from effector CD8(+) T cell-transferred C57BL/6 mice, respectively. We then assessed kinetics of T cell survival using PE-H2-K(b)/OVAI tetramer and FITC-CD8 staining by flow cytometry. We found that survival of transferred effector and memory CD8(+) T cells in CD54(-/-) mice significantly decreased (p<0.05) compared to that in C57BL/6 mice due to an increased T cell apoptosis, which is mediated via downregulation of proapoptotic Bid, anti-apoptotic Bcl-2, Bcl-X(L) and pro-Caspase-8, and up-regulation of apoptotic Bax and cleaved Caspase-3 and -7 by RNA array and Western blotting analyses. Decreased expression of CD27 and IL-15R on transferred CD8(+) T cells with less survival was found to be associated with increased T cell apoptosis, which was confirmed by silencing CD27 with siRNA transfection or using CD8(+) (IL-15R(-/-))T cells for adoptive transfer into C57BL/6 mice. These data indicate that LFA-1 signal defect-induced CD8(+) T cell apoptosis is associated with reduced CD27 costimulation and IL-15R survival signal. Therefore, our study provides important evidence on and elucidates the molecular mechanism associated with the role LFA-1 signaling plays in effector and memory CD8(+) T cell survival.

Memory CD8+ T cell differentiation

In response to infection or effective vaccination, naive antigen-specific CD8+ T cells undergo a dramatic highly orchestrated activation process. Initial encounter with an appropriately activated antigen-presenting cell leads to blastogenesis and an exponential increase in antigen-specific CD8+ T cell numbers. Simultaneously, a dynamic differentiation process occurs, resulting in formation of both primary effector and long-lived memory cells. Current findings have emphasized the heterogeneity of effector and memory cell populations with the description of multiple cellular subsets based on phenotype, function, and anatomic location. Yet, only recently have we begun to dissect the underlying factors mediating the temporal control of the development of distinct effector and memory CD8+ T cell sublineages. In this review we will focus on the requirements for mounting an effective CD8+ T cell response and highlight the elements regulating the differentiation of effector and memory subsets.

Oncostatin M enhances the antiviral effects of type I interferon and activates immunostimulatory functions in liver epithelial cells

Oncostatin M (OSM) is released together with type I interferon (IFN) by activated dendritic cells, suggesting a concerted action of these cytokines in the biological response against infection. We found that OSM increases the antiviral effect of IFN-alpha in Huh7 hepatoma cells infected with hepatitis A or hepatitis C virus and synergizes with IFN-alpha in the induction of antiviral genes. The combination of OSM and IFN-alpha led to upregulation of both STAT1 and STAT3 together with intense and prolonged activation of STAT1, STAT3, and Jak1. OSM with or without IFN-alpha also activated p38 mitogen-activated protein kinase, which is known to enhance transcription of IFN-alpha-inducible genes. Interestingly, OSM combined with IFN-alpha strongly induced immunoproteasome genes and other genes involved in antigen processing and presentation. Moreover, OSM, alone or in combination with IFN-alpha, upregulated relevant innate immunity molecules and increased the expression of intracellular adhesion molecule 1 and interleukin-15 receptor alpha (IL-15Ralpha) in liver cells. Hepatoma cells transfected with a plasmid encoding a viral antigen were able to activate effector T cells when pretreated with IFN-alpha plus OSM but not with each cytokine separately. Also, OSM, more than IFN-alpha, augmented the ability of Huh7 cells to transpresent IL-15 to responding lymphocytes and increased the immunostimulatory activity of liver epithelial cells by presenting a short viral peptide to sensitized cytotoxic T cells. In conclusion, OSM enhances the antiviral effects of type I interferon and cooperates with it in the induction of adaptive immune responses to pathogens. These findings may have therapeutic implications.

Strategic nonmyeloablative conditioning: CD154:CD40 costimulatory blockade at primary bone marrow transplantation promotes engraftment for secondary bone marrow transplantation after engraftment failure

There is an increased risk of failure of engraftment following nonmyeloablative conditioning. Sensitization resulting from failed bone marrow transplantation (BMT) remains a major challenge for secondary BMT. Approaches to allow successful retransplantation would have significant benefits for BMT candidates living with chronic diseases. We used a mouse model to investigate the effect of preparative regimens at primary BMT on outcome for secondary BMT. We found that conditioning with TBI or recipient T cell lymphodepletion at primary BMT did not promote successful secondary BMT. In striking contrast, successful secondary BMT could be achieved in mice conditioned with anti-CD154 costimulatory molecule blockade at first BMT. Blockade of CD154 alone or combined with T cell depletion inhibits generation of the humoral immune response after primary BMT, as evidenced by abrogation of production of anti-donor Abs. The humoral barrier is dominant in sensitization resulting from failed BMT, because almost all CFSE-labeled donor cells were killed at 0.5 and 3 h in sensitized recipients in in vivo cytotoxicity assay, reflecting Ab-mediated cytotoxicity. CD154:CD40 costimulatory blockade used at primary BMT promotes allogeneic engraftment in secondary BMT after engraftment failure at first BMT. The prevention of generation of anti-donor Abs at primary BMT is critical for successful secondary BMT.

CD54 is a surrogate marker of antigen presenting cell activation

There is no single universally accepted hallmark of antigen presenting cell (APC) activation. Instead a variety of methods are used to identify APCs and assess their activation state. These activation measures include phenotypic methods [e.g., assessing the increased expression of surface markers such as major histocompatability (MHC) class II] and functional assays (e.g., evaluating the enhanced ability to take up and process antigen, or stimulate naïve T cells). Sipuleucel-T is an investigational autologous active cellular immunotherapy product designed to stimulate a T cell immune response against human prostatic acid phosphatase (PAP), an antigen highly expressed in prostate tissue. Sipuleucel-T consists of peripheral blood mononuclear cells (PBMCs), including activated APCs displaying epitopes of PAP. In order to develop a robust reproducible potency assay that is not hampered by MHC restriction we have developed a method to simply assess the biological activation of antigen presenting cells (APCs). In the course of sipuleucel-T characterization, we analyzed various phenotypic and functional parameters to define the activation state of APCs obtained from peripheral blood. Flow cytometric assays revealed that CD54+ cells are responsible for antigen uptake, and that expression of CD54 predominantly localizes to APCs. Costimulation, as measured by an allogeneic mixed lymphocytic reaction (alloMLR) assay, showed that activity was restricted to the CD54+ cell population. Similarly, CD54+ cells harbor all of the PAP-specific antigen presentation activity, as assayed using a PAP-specific HLA-DRbeta1-restricted T cell hybridoma. Finally we show that CD54 expression is substantially and consistently upregulated on APCs during culture with a GM-CSF fusion protein, and that this upregulation activity can be quantified. Thus these data support the use of CD54 upregulation as a surrogate for assessing human APC activation and validates its utility as a potency measure of sipuleucel-T.

Intercellular adhesion molecule-1-dependent stable interactions between T cells and dendritic cells determine CD8+ T cell memory

The initiation of cytotoxic immune responses requires the direct interaction between naive CD8+ T lymphocytes and dendritic cells (DCs). Multiphoton imaging in intact lymph nodes (LNs) showed that during priming, naive T cells and DCs establish sequentially brief (i.e., minutes) and long (hours) antigen-specific contacts. We show here that the expression of the Intercellular Adhesion Molecule-1 (ICAM-1) by mature DCs is critical for long-lasting contacts with CD8+ T cells but dispensable for short-lived antigen-specific interactions. Serial brief DC-T cell contacts induced early CD8+ T cell activation, proliferation, and differentiation into effector cytotoxic T lymphocytes in the first few days after immunization. ICAM-1-deficient mature DCs, however, failed to induce fully effective priming, because CD8+ T cells produced reduced amounts of interferon gamma and were clonally depleted after 2 weeks. In addition, Icam1(-/-) mice failed to respond to rechallenge. We conclude that ICAM-1-dependent long-lasting interactions between mature DCs and naive CD8+ T cells determine the survival of activated CD8+ T cells and the establishment of effective memory.

Functional characterization of natural killer cells in type I leukocyte adhesion deficiency

In this study, we analyzed IL-2–activated polyclonal natural killer (NK) cells derived from 2 patients affected by leukocyte adhesion deficiency type I (LAD1), an immunodeficiency characterized by mutations of the gene coding for CD18, the β subunit shared by major leukocyte integrins. We show that LAD1 NK cells express normal levels of various triggering NK receptors (and coreceptors) and that mAb-mediated engagement of these receptors results in the enhancement of both NK cytolytic activity and cytokine production. Moreover, these activating NK receptors were capable of recognizing their specific ligands on target cells. Thus, LAD1 NK cells, similarly to normal NK cells, were capable of killing most human tumor cells analyzed and produced high amounts of IFN-γ when cocultured in presence of target cells. Murine target cells represented a common exception, as they were poorly susceptible to LAD1 NK cells. Finally, LAD1 NK cells could efficiently kill or induce maturation of monocyte-derived immature dendritic cells (DCs). Altogether our present study indicates that in LAD1 patients, 3 important functions of NK cells (eg, cytotoxicity, IFN-γ production, and DC editing) are only marginally affected and provides new insight on the cooperation between activating receptors and LFA-1 in the induction of NK cell activation and function.