TIGIT mediates activation-induced cell death of ILC2s during chronic airway allergy

While group-2 innate lymphoid cells (ILC2s) are highly proliferative in allergic inflammation, the removal of overactivated ILC2s in allergic diseases has not been investigated. We previously showed that chronic airway allergy induces "exhausted-like" dysfunctional ILC2s expressing T cell immunoreceptor with Ig and ITIM domains (TIGIT). However, the physiological relevance of these cells in chronic allergy remains elusive. To precisely identify and monitor TIGIT+ ILC2s, we generated TIGIT lineage tracer mice. Chronic allergy stably induced TIGIT+ ILC2s, which were highly activated, apoptotic, and were quickly removed from sites of chronic allergy. Transcripts from coding genes were globally suppressed in the cells, possibly due to reduced chromatin accessibility. Cell death in TIGIT+ ILC2s was enhanced by interactions with CD155 expressed on macrophages, whereas genetic ablation of Tigit or blockade by anti-TIGIT antagonistic antibodies promoted ILC2 survival, thereby deteriorating chronic allergic inflammation. Our work demonstrates that TIGIT shifts the fate of ILC2s toward activation-induced cell death, which could present a new therapeutic target for chronic allergies.

Omicron infection-associated T- and B-cell immunity in antigen-naive and triple-COVID-19-vaccinated individuals

Since early 2022, various Omicron variants have dominated the SARS-CoV-2 pandemic in most countries. All Omicron variants are B-cell immune escape variants, and antibodies induced by first-generation COVID-19 vaccines or by infection with earlier SARS-CoV-2 variants largely fail to protect individuals from Omicron infection. In the present study, we investigated the effect of Omicron infections in triple-vaccinated and in antigen-naive individuals. We show that Omicron breakthrough infections occurring 2-3.5 months after the third vaccination restore B-cell and T-cell immune responses to levels similar to or higher than those measured 14 days after the third vaccination, including the induction of Omicron-neutralizing antibodies. Antibody responses in breakthrough infection derived mostly from cross-reacting B cells, initially induced by vaccination, whereas Omicron infections in antigen-naive individuals primarily generated B cells binding to the Omicron but not the Wuhan spike protein. Although antigen-naive individuals mounted considerable T-cell responses after infection, B-cell responses were low, and neutralizing antibodies were frequently below the limit of detection. In summary, the detection of Omicron-associated B-cell responses in primed and in antigen-naive individuals supports the application of Omicron-adapted COVID-19 vaccines, but calls into question their suitability if they also contain/encode antigens of the original Wuhan virus.

Establishment and Functional Characterization of Murine Monoclonal Antibodies Recognizing Neuritin

Neuritin represents a neurotrophic factor that is not only important in neuronal development and plasticity but also impacts endothelial angiogenesis, cell migration, tumor growth and the production of antibodies by B cells. We established monoclonal mouse anti-mouse neuritin antibodies by immunizing knock-out mice with two different neuritin-derived peptides. Because neuritin is well conserved between species, these new monoclonal antibodies recognize the neuritin of a wide variety of species, including human. Moreover, they not only recognize specifically surface-bound neuritin expressed by murine follicular regulatory T cells but also the block binding of recombinant neuritin to germinal center B cells. This suggests that these newly generated tools will be of great use in studying neuritin expression and function.

Longitudinal Tracking of Immune Responses in COVID-19 Convalescents Reveals Absence of Neutralization Activity Against Omicron and Staggered Impairment to Other SARS-CoV-2 Variants of Concern

Evaluating long-term protection against SARS-CoV-2 variants of concern in convalescing individuals is of high clinical relevance. In this prospective study of a cohort of 46 SARS-CoV-2 patients infected with the Wuhan strain of SARS-CoV-2 we longitudinally analyzed changes in humoral and cellular immunity upon early and late convalescence. Antibody neutralization capacity was measured by surrogate virus neutralization test and cellular responses were investigated with 31-colour spectral flow cytometry. Spike-specific, isotype-switched B cells developed already during the disease phase, showed a memory phenotype and did not decrease in numbers even during late convalescence. Otherwise, no long-lasting perturbations of the immune compartment following COVID-19 clearance were observed. During convalescence anti-Spike (S1) IgG antibodies strongly decreased in all patients. We detected neutralizing antibodies against the Wuhan strain as well as the Alpha and Delta but not against the Beta, Gamma or Omicron variants for up to 7 months post COVID-19. Furthermore, correlation analysis revealed a strong association between sera anti-S1 IgG titers and their neutralization capacity against the Wuhan strain as well as Alpha and Delta. Overall, our data suggest that even 7 month after the clearance of COVID-19 many patients possess a protective layer of immunity, indicated by the persistence of Spike-specific memory B cells and by the presence of neutralizing antibodies against the Alpha and Delta variants. However, lack of neutralizing antibodies against the Beta, Gamma and Omicron variants even during the peak response is of major concern as this indicates viral evasion of the humoral immune response.

Identification of Follicular T Cells in the Gut

Humoral adaptive immune responses trigger the establishment of plasma B cells secreting antibodies of various isotypes that bind antigen specifically and with high affinity. Moreover, memory B cells will be generated. To accomplish this, B cells need assistance from a special subset of CD4 T cells, the so called follicular T cells that differentiate from naïve T cells in the course of the immune response. Therefore, the study of follicular T cells is of primordial interest when investigating the molecular and cellular determinants of adaptive immune responses. This is done by direct analysis of the cells isolated from mice following an immunological challenge but in many instances such analyses must involve follow-up studies in cell culture requiring living cells. Especially, in vitro experimentation necessitates isolation and sorting of follicular T cells. However, follicular T cells are generally difficult to handle because they are prone to apoptosis and cell death. This is particularly evident when dealing with follicular T cells residing in the gut since we observed that isolation and processing from murine gut notoriously results in very high loss rates when compared for example to cells obtained from immunized peripheral lymph nodes. To bypass these limitations, we developed a protocol that allows for efficient isolation of intact follicular T cells. The protocol introduced here illustrates isolation and handling of follicular T cells using murine Peyer's Patches as an example because they constantly harbor significant amounts of these cells.

The impact of stress on the transcriptomic signature of iNKT1 cells

Invariant natural killer T (iNKT) cells develop in thymus before emigrating and settling peripheral tissues and organs. In contrast to regular naïve T cells, most iNKT cells do not continuously recirculate but are rather sessile and can adopt phenotypically as well as functionally to their tissue environment. To explore this in more detail, we focused on the most widely distributed CD4⁺iNKT1 cells and compared the transcriptome of cells isolated from liver and spleen. Whereas there are only very few genuine differences in the transcriptomes of CD4⁺iNKT1 cells of these two organs, the mode of cell isolation left clear marks in the transcriptomic signature. In contrast to liver cell isolated in the cold, cells prepared by enzymatic tissue digestion upregulated quickly a series of genes known to respond to stress. Therefore, to avoid erroneous conclusions, a comparison of expression profiles must take into consideration the history of cell preparation.

Targeted delivery of regulatory macrophages to lymph nodes interferes with T cell priming by preventing the formation of stable immune synapses

Immunosuppressive myeloid cells are frequently induced in tumors and attenuate anti-tumor effector functions. In this study, we differentiate immunosuppressive regulatory macrophages (Mregs) from hematopoietic progenitors and test their potential to suppress adaptive immune responses in lymph nodes. Targeted delivery of Mregs to lymph nodes is facilitated by retroviral overexpression of the chemokine receptor CCR7 and intra-lymphatic cell application. Delivery of Mregs completely abolishes the priming of cognate CD8 cells and strongly reduces delayed-type hypersensitivity reactions. Mreg-mediated T cell suppression requires cell-cell contact-regulated nitric oxide production. Two-photon microscopy reveals that nitric oxide produced by Mregs reduces the interaction duration between dendritic cells and T cells. Exposure of activated T cells to nitric oxide strongly reduces their binding to ICAM-1, indicating that nitrosylation of proteins involved in cell adhesion affects synapse formation. Thus, this study identifies a mechanism of myeloid cell-mediated immune suppression and provides an approach for its therapeutic use.

Impact of Aging on the Phenotype of Invariant Natural Killer T Cells in Mouse Thymus

Invariant natural killer T (iNKT) cells represent a subclass of T cells possessing a restricted repertoire of T cell receptors enabling them to recognize lipid derived ligands. iNKT cells are continuously generated in thymus and differentiate into three main subpopulations: iNKT1, iNKT2, and iNKT17 cells. We investigated the transcriptomes of these subsets comparing cells isolated from young adult (6–10 weeks old) and aged BALB/c mice (25–30 weeks of age) in order to identify genes subject to an age-related regulation of expression. These time points were selected to take into consideration the consequences of thymic involution that radically alter the existing micro-milieu. Significant differences were detected in the expression of histone genes affecting all iNKT subsets. Also the proliferative capacity of iNKT cells decreased substantially upon aging. Several genes were identified as possible candidates causing significant age-dependent changes in iNKT cell generation and/or function such as genes coding for granzyme A, ZO-1, EZH2, SOX4, IGF1 receptor, FLT4, and CD25. Moreover, we provide evidence that IL2 differentially affects homeostasis of iNKT subsets with iNKT17 cells engaging a unique mechanism to respond to IL2 by initiating a slow rate of proliferation.

Low serum neutralizing anti-SARS-CoV-2 S antibody levels in mildly affected COVID-19 convalescent patients revealed by two different detection methods

Neutralizing antibodies targeting the receptor-binding domain (RBD) of the SARS-CoV-2 spike (S) block severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) entry into cells via surface-expressed angiotensin-converting enzyme 2 (ACE2). We used a surrogate virus neutralization test (sVNT) and SARS-CoV-2 S protein-pseudotyped vesicular stomatitis virus (VSV) vector-based neutralization assay (pVNT) to assess the degree to which serum antibodies from coronavirus disease 2019 (COVID-19) convalescent patients interfere with the binding of SARS-CoV-2 S to ACE2. Both tests revealed neutralizing anti-SARS-CoV-2 S antibodies in the sera of ~90% of mildly and 100% of severely affected COVID-19 convalescent patients. Importantly, sVNT and pVNT results correlated strongly with each other and to the levels of anti-SARS-CoV-2 S1 IgG and IgA antibodies. Moreover, levels of neutralizing antibodies correlated with the duration and severity of clinical symptoms but not with patient age. Compared to pVNT, sVNT is less sophisticated and does not require any biosafety labs. Since this assay is also much faster and cheaper, sVNT will not only be important for evaluating the prevalence of neutralizing antibodies in a population but also for identifying promising plasma donors for successful passive antibody therapy.

Increasing the throughput of label-free cell assays to study the activation of G-protein-coupled receptors by using a serial agonist exposure protocol

Label-free, holistic assays, monitoring, for example, the impedance of cells on electrodes, are gaining increasing popularity in the evaluation of G-protein-coupled receptor (GPCR) ligands. It is the strength of these approaches to provide the integrated cellular response non-invasively, highly automated and with a device-dependent time resolution down to several milliseconds. With an increasing number of samples to be studied in parallel, the available time resolution is, however, reduced and the cost for the disposable sensor arrays may become limiting. Inspired by protocols from organ pharmacology, we investigated a simple serial agonist addition assay that circumvents these limitations in impedance-based cellular assays. Using a serial addition of increasing concentrations of a GPCR agonist while continuously monitoring the sample's impedance, we were able to establish a full concentration-response curve for the endogenous agonist histamine on a single layer of U-373 MG cells endogenously expressing the histamine 1 receptor (H1R). This approach is validated with respect to conventional, parallel agonist addition protocols and studies using H1R antagonists such as mepyramine. Applicability of the serial agonist addition assay was shown for other GPCRs known for their signaling via one of the canonical G-protein pathways, Gq, Gi/0 or Gs as well. The serial agonist addition protocol has the potential to further strengthen the output of label-free analysis of GPCR activation.

Laquinimod, a prototypic quinoline-3-carboxamide and aryl hydrocarbon receptor agonist, utilizes a CD155-mediated natural killer/dendritic cell interaction to suppress CNS autoimmunity

Background

Quinoline-3-carboxamides, such as laquinimod, ameliorate CNS autoimmunity in patients and reduce tumor cell metastasis experimentally. Previous studies have focused on the immunomodulatory effect of laquinimod on myeloid cells. The data contained herein suggest that quinoline-3-carboxamides improve the immunomodulatory and anti-tumor effects of NK cells by upregulating the adhesion molecule DNAX accessory molecule-1 (DNAM-1).

Methods

We explored how NK cell activation by laquinimod inhibits CNS autoimmunity in experimental autoimmune encephalomyelitis (EAE), the most utilized model of MS, and improves immunosurveillance of experimental lung melanoma metastasis. Functional manipulations included in vivo NK and DC depletion experiments and in vitro assays of NK cell function. Clinical, histological, and flow cytometric read-outs were assessed.

Results

We demonstrate that laquinimod activates natural killer (NK) cells via the aryl hydrocarbon receptor and increases their DNAM-1 cell surface expression. This activation improves the cytotoxicity of NK cells against B16F10 melanoma cells and augments their immunoregulatory functions in EAE by interacting with CD155⁺ dendritic cells (DC). Noteworthy, the immunosuppressive effect of laquinimod-activated NK cells was due to decreasing MHC class II antigen presentation by DC and not by increasing DC killing.

Conclusions

This study clarifies how DNAM-1 modifies the bidirectional crosstalk of NK cells with CD155⁺ DC, which can be exploited to suppress CNS autoimmunity and strengthen tumor surveillance.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1437-0) contains supplementary material, which is available to authorized users.

Initial Characterization of Transgenic Mice Overexpressing Human Histamine H2 Receptors

In an integrative approach, we studied the role of histamine H₂ receptors in the mouse heart. We noted that histamine, added cumulatively to the organ bath, failed to affect the force of contraction in left atrial preparations and did not change spontaneous heart rate in right atrial preparations from wild-type mice. By contrast, in the same preparations from mice that overexpressed the human H₂ receptor in a cardiac-specific way, histamine exerted concentration- and time-dependent positive inotropic and positive chronotropic effects. Messenger RNA of the human H₂ receptor was only detected in transgenic mice. Likewise, immunohistology and autoradiography only gave signals in transgenic but not in wild-type cardiac preparations. Similarly, a positive inotropic and positive chronotropic effect was observed with histamine in echocardiography of living transgenic mice and isolated perfused hearts (Langendorff preparation). Phosphorylation of phospholamban was increased in atrial and ventricular preparations from transgenic mice, but not in wild-type animals. The effects of histamine were mimicked by dimaprit and amthamine and antagonized by cimetidine. In summary, we generated a new model to study the physiologic and pathophysiologic cardiac role of the human H₂ receptor.

The negative effect of unloading exceeds the bone-sparing effect of alkaline supplementation: a bed rest study

Potassium bicarbonate was administrated to an already alkaline diet in seven male subjects during a 21-day bed rest study and was able to decrease bed rest induced increased calcium excretion but failed to prevent bed rest-induced bone resorption.

INTRODUCTION

Supplementation with alkali salts appears to positively influence calcium and bone metabolism and, thus, could be a countermeasure for population groups with an increased risk for bone loss. However, the extent to which alkalization counteracts acid-induced bone resorption or whether it merely has a calcium and bone maintenance effect is still not completely understood. In the present study, we hypothesized that additional alkalization to an already alkaline diet can further counteract bed rest-induced bone loss.

METHODS

Seven healthy male subjects completed two parts of a crossover designed 21-day bed rest study: bed rest only (control) and bed rest supplemented with 90 mmol potassium bicarbonate (KHCO₃) daily.

RESULTS

KHCO₃supplementation during bed rest resulted in a more alkaline status compared to the control intervention, demonstrated by the increase in pH and buffer capacity level (pH p = 0.023, HCO₃p = 0.02, ABE p = 0.03). Urinary calcium excretion was decreased during KHCO₃ supplementation (control 6.05 ± 2.74 mmol/24 h; KHCO₃ 4.87 ± 2.21 mmol/24 h, p = 0.03); whereas, bone formation was not affected by additional alkalization (bAP p = 0.58; PINP p = 0.60). Bone resorption marker UCTX tended to be lower during alkaline supplementation (UCTX p = 0.16).

CONCLUSIONS

The more alkaline acid-base status, achieved by KHCO₃ supplementation, reduced renal calcium excretion during bed rest, but was not able to prevent immobilization-induced bone resorption. However, advantages of alkaline salts on bone metabolism may occur under acidic metabolic conditions or with respect to the positive effect of reduced calcium excretion within a longer time frame.

TRIAL REGISTRATION

Trial number: NCT01509456.

Coming of Age: CD96 Emerges as Modulator of Immune Responses

CD96 represents a type I transmembrane glycoprotein belonging to the immunoglobulin superfamily. CD96 is expressed mainly by cells of hematopoietic origin, in particular on T and NK cells. Upon interaction with CD155 present on target cells, CD96 was found to inhibit mouse NK cells, and absence of this interaction either by blocking with antibody or knockout of CD96 showed profound beneficial effects in containment of tumors and metastatic spread in murine model systems. However, our knowledge regarding CD96 functions remains fragmentary. In this review, we will discuss structural features of CD96 and their putative impact on function as well as some unresolved issues such as a potential activation that may be conferred by human but not mouse CD96. This is of importance for translation into human cancer therapy. We will also address CD96 activities in the context of the immune regulatory network that consists of CD155, CD96, CD226, and TIGIT.

Shared and Unique Features Distinguishing Follicular T Helper and Regulatory Cells of Peripheral Lymph Node and Peyer's Patches

Follicular helper (TFH) and regulatory (TFR) cells are critical players in managing germinal center (GC) reactions that accomplish effective humoral immune responses. Transcriptome analyses were done comparing gene regulation of TFH and TFR cells isolated from Peyer’s Patches (PP) and immunized peripheral lymph nodes (pLNs) revealing many regulatory patterns common to all follicular cells. However, in contrast to TFH cells, the upregulation or downregulation of many genes was attenuated substantially in pLN TFR cells when compared to those of PP. Additionally, PP but not pLN TFR cells were largely unresponsive to IL2 and expressed Il4 as well as Il21. Together with fundamental differences in gene expression that were found between cells of both compartments this emphasizes specific adaptations of follicular T cell functions to their micro-milieu. Moreover, although GL7 expression distinguishes matured follicular T cells, GL7⁺ as well as GL7⁻ cells are present in the GC.

Blocking the ART2.2/P2X7-system is essential to avoid a detrimental bias in functional CD4 T cell studies

Murine T cell subsets differ in their expression level of P2X7. Depending on several parameters like extracellular NAD⁺ , P2X7 can be ADP-ribosylated rapidly by adjacent ARTC2.2 resulting in susceptibilities to apoptosis to a varying extent. This detrimental effect can be prevented when drugs like KN-62 are present during cell preparations.

CD96 targeted antibodies need not block CD96-CD155 interactions to promote NK cell anti-metastatic activity

CD96 is a transmembrane glycoprotein Ig superfamily receptor, expressed on various T cell subsets and NK cells, that interacts with nectin and nectin-like proteins, including CD155/polio virus receptor (PVR). Here, we have compared three rat anti-mouse CD96 mAbs, including two that block CD96-CD155 (3.3 and 6A6) and one that does not block CD96-CD155 (8B10). Using flow cytometry, we demonstrated that both mAbs 3.3 and 6A6 bind to the first Ig domain of mouse CD96 and compete with CD155 binding, while mAb 8B10 binds to the second Ig domain and does not block CD155. While Fc isotype was irrelevant concerning the anti-metastatic activity of 3.3 mAb, in four different experimental metastases models and one spontaneous metastasis model, the relative order of anti-metastatic potency was 6A6 > 3.3 > 8B10. The metastatic burden control of all of the anti-CD96 clones was highly dependent on NK cells and IFN-γ. Consistent with its inability to block CD96-CD155 interactions, 8B10 retained anti-metastatic activity in CD155-deficient mice, whereas 3.3 and 6A6 lost potency in CD155-deficient mice. Furthermore, 8B10 retained most of its anti-metastatic activity in IL-12p35-deficient mice whereas the activity of 3.3 and 6A6 were partially lost. All three mAbs were inactive in CD226-deficient mice. Altogether, these data demonstrate anti-CD96 need not block CD96-CD155 interactions (ie. immune checkpoint blockade) to promote NK cell anti-metastatic activity.

Expression of CD226 is associated to but not required for NK cell education

DNAX accessory molecule-1 (DNAM-1, also known as CD226) is an activating receptor expressed on subsets of natural killer (NK) and T cells, interacts with its ligands CD155 or CD112, and has co-varied expression with inhibitory receptors. Since inhibitory receptors control NK-cell activation and are necessary for MHC-I-dependent education, we investigated whether DNAM-1 expression is also involved in NK-cell education. Here we show an MHC-I-dependent correlation between DNAM-1 expression and NK-cell education, and an association between DNAM-1 and NKG2A that occurs even in MHC class I deficient mice. DNAM-1 is expressed early during NK-cell development, precedes the expression of MHC-I-specific inhibitory receptors, and is modulated in an education-dependent fashion. Cd226^−/− mice have missing self-responses and NK cells with a normal receptor repertoire. We propose a model in which NK-cell education prevents or delays downregulation of DNAM-1. This molecule endows educated NK cells with enhanced effector functions but is dispensable for education.

CD226 is an activating receptor expressed in a co-varied manner with inhibitory receptors on natural killer (NK) cells, but whether CD226 is involved in NK cell education is unclear. Here the authors show that CD226 expression is plastic depending on the MHC environment and endows educated NK cells enhanced effector functions.

Label-free versus conventional cellular assays: Functional investigations on the human histamine H1 receptor

A set of histamine H₁ receptor (H₁R) agonists and antagonists was characterized in functional assays, using dynamic mass redistribution (DMR), electric cell-substrate impedance sensing (ECIS) and various signaling pathway specific readouts (Fura-2 and aequorin calcium assays, arrestin recruitment (luciferase fragment complementation) assay, luciferase gene reporter assay). Data were gained from genetically engineered HEK293T cells and compared with reference data from GTPase assays and radioligand binding. Histamine and the other H₁R agonists gave different assay-related pEC₅₀ values, however, the order of potency was maintained. In the luciferase fragment complementation assay, the H₁R preferred β-arrestin2 over β-arrestin1. The calcium and the impedimetric assay depended on G_q coupling of the H₁R, as demonstrated by complete inhibition of the histamine-induced signals in the presence of the G_q inhibitor FR900359 (UBO-QIC). Whereas partial inhibition by FR900359 was observed in DMR and the gene reporter assay, pertussis toxin substantially decreased the response in DMR, but increased the luciferase signal, reflecting the contribution of both, G_q and G_i, to signaling in these assays. For antagonists, the results from DMR were essentially compatible with those from conventional readouts, whereas the impedance-based data revealed a trend towards higher pK_b values. ECIS and calcium assays apparently only reflect G_q signaling, whereas DMR and gene reporter assays appear to integrate both, G_q and G_i mediated signaling. The results confirm the value of the label-free methods, DMR and ECIS, for the characterization of H₁R ligands. Both noninvasive techniques are complementary to each other, but cannot fully replace reductionist signaling pathway focused assays.

Distinct gene expression patterns correlate with developmental and functional traits of iNKT subsets

Invariant natural killer T (iNKT) cells comprise a subpopulation of innate lymphocytes developing in thymus. A new model proposes subdividing murine iNKT cells into iNKT1, 2 and 17 cells. Here, we use transcriptome analyses of iNKT1, 2 and 17 subsets isolated from BALB/c and C57BL/6 thymi to identify candidate genes that may affect iNKT cell development, migration or function. We show that Fcɛr1γ is involved in generation of iNKT1 cells and that SerpinB1 modulates frequency of iNKT17 cells. Moreover, a considerable proportion of iNKT17 cells express IL-4 and IL-17 simultaneously. The results presented not only validate the usefulness of the iNKT1/2/17-concept but also provide new insights into iNKT cell biology.

[The Effect of Intraoperative Screw Monitoring (Root Monitoring) with the INS-1 System (NUVASIVE) on the Radiological Outcome of Dorsal Instrumentation of the Lumbar Spine]

INTRODUCTION

Transpedicular screw fixation of spinal segments has been described for a variety of surgical indications and is a key element in spinal surgery. The aim of transpedicular screw fixation is to achieve maximal stability. Screw malposition should be obviated to avoid neurological complications. There are published methods of applying evoked EMG to control screw position in relation to neural structures. These studies demonstrated that an intact bony pedicle wall acts as an electrical isolator between the screw and spinal nerve root. The aim of our study was to evaluate the impact of intraoperative pedicle screw monitoring on screw positioning.

MATERIAL AND METHODS

We enrolled 22 patients in this prospective randomised study, who underwent spinal instrumentation after being split into two equal groups. In the first group, dorsal instrumentation was supplemented with intraoperative nerve root monitoring using the INS-1-System (NuVasive, San Diego USA). In the second group, screws were inserted without additional pedicle monitoring. All patients underwent monosegmental instrumentation with "free hand implanted" pedicle screws. 44 screws were inserted in each group. The screw position was evaluated postoperatively using CT scans. The position of the screws in relation to the pedicle was measured in three different planes: sagittal, axial and coronal. The accuracy of the screw position was described using the Berlemann classification system. Screw position is classified in three groups: type 1 correct screw position, type 2 encroachment on the inner cortical wall, type 3 pedicle cortical perforation. Screw angulation and secondary operative criteria were also evaluated.

RESULTS

The use of neuromonitoring did not influence the distance between the centre of the screws and the pedicle wall. Distances only depended on the implantation side (right and left) and the height of implantation (caudal or cranial screw). Because of the low number of cases, no conclusion could be reached about the influence of root monitoring on the correct positioning of the screws. There was at least a non-significant trend towards more frequent perforation of the pedicle in the monitor group. In the present study, we showed that root monitoring had a significant effect on the scattering of transversal angles. These were increased compared to the control group. Otherwise, the implantation angle was not shown to depend on the use of neuromonitoring. Neuromonitoring did not influence blood loss or operative time.

DISCUSSION

The data did not permit any conclusion as to whether this technique can minimise the frequency of pedicle screw malposition. The four coronal plane distances did not depend on the use of neuromonitoring. The inclination angle was also unaffected by neuromonitoring. The only parameter for which we found any effect was the transverse angle. The mean values were similar in both groups, but the variances were not equal. The effect of monitoring on the only parameter which could not be evaluated by fluoroscopy is thus rather unfavourable.

Sensitivity of dendritic cells to NK-mediated lysis depends on the inflammatory environment and is modulated by CD54/CD226-driven interactions

Previous studies have suggested that NK cells may limit T cell responses by their ability to eradicate dendritic cells, as demonstrated by NK cell-mediated killing of dendritic cells generated from mouse bone marrow cells or human monocytes with GM-CSF. In the present study, we demonstrated that conventional dendritic cells, generated in vitro with Flt3 ligand or from spleens, were resistant to NK cell-mediated lysis. However, upon stimulation with GM-CSF, NK cells could mediate lysis of these dendritic cells. GM-CSF-stimulated Flt3 ligand dendritic cells or splenic dendritic cells increased surface expression of costimulatory molecules and known NK cell ligands. Likewise, NK cells could target dendritic cells in vivo, which could be inhibited, in part, by anti-GM-CSF antibodies. The blocking of CD54 or CD226 inhibited NK cell-mediated cytotoxicity of the GM-CSF-stimulated Flt3 ligand conventional dendritic cells. Furthermore, the CD226⁺NKG2A^- subset of NK cells was selectively better at targeting GM-CSF-stimulated Flt3 ligand conventional dendritic cells. However, CD155, a known ligand for CD226, could also act as an inhibitor of NK cell-mediated lysis, as dendritic cells lacking CD155 were more sensitive to NK cell-mediated lysis than wild-type dendritic cells. We hypothesize that by only permitting a subset of NK cells to target activated dendritic cells during inflammation, this would allow the immune system to balance between dendritic cells able to drive adaptive immune responses and dendritic cells targeted for elimination by NK cells to hinder, e.g., spread of infection.

Suppression of Metastases Using a New Lymphocyte Checkpoint Target for Cancer Immunotherapy

CD96 has recently been shown as a negative regulator of mouse natural killer (NK)-cell activity, with Cd96(-/-)mice displaying hyperresponsive NK cells upon immune challenge. In this study, we have demonstrated that blocking CD96 with a monoclonal antibody inhibited experimental metastases in three different tumor models. The antimetastatic activity of anti-CD96 was dependent on NK cells, CD226 (DNAM-1), and IFNγ, but independent of activating Fc receptors. Anti-CD96 was more effective in combination with anti-CTLA-4, anti-PD-1, or doxorubicin chemotherapy. Blocking CD96 in Tigit(-/-)mice significantly reduced experimental and spontaneous metastases compared with its activity in wild-type mice. Co-blockade of CD96 and PD-1 potently inhibited lung metastases, with the combination increasing local NK-cell IFNγ production and infiltration. Overall, these data demonstrate that blocking CD96 is a new and complementary immunotherapeutic strategy to reduce tumor metastases.

SIGNIFICANCE

This article illustrates the antimetastatic activity and mechanism of action of an anti-CD96 antibody that inhibits the CD96-CD155 interaction and stimulates NK-cell function. Targeting host CD96 is shown to complement surgery and conventional immune checkpoint blockade.

Differential Effects of Gut-Homing Molecules CC Chemokine Receptor 9 and Integrin-β7 during Acute Graft-versus-Host Disease of the Liver

Homing of allogeneic donor T cells to recipient tissue is imperative for the development of acute graft-versus-host disease (GVHD) after bone marrow transplantation (BMT). In this study we show that alteration of T cell homing due to integrin-β7 deficiency on T cells or its ligand MAdCAM-1 in BMT recipients contributes to the pathophysiology of experimental GVHD. In contrast, lack of CC chemokine receptor 9 on donor T cells alters tissue homing but does not impact GVHD survival. We further demonstrate that MAdCAM-1 is aberrantly expressed in hepatic murine GVHD as well as in patients with active liver GVHD. However, infiltration of donor T cells in gut but not liver was dependent of MAdCAM-1 expression, indicating, that homing and/or retention of donor T cells rests on divergent molecular pathways depending on the GVHD target tissue.

Molecular determinants for the high constitutive activity of the human histamine H4 receptor: functional studies on orthologues and mutants

BACKGROUND AND PURPOSE

Some histamine H4 receptor ligands act as inverse agonists at the human H4 receptor (hH4 R), a receptor with exceptionally high constitutive activity, but as neutral antagonists or partial agonists at the constitutively inactive mouse H4 receptor (mH4 R) and rat H4 receptor (rH4 R). To study molecular determinants of constitutive activity, H4 receptor reciprocal mutants were constructed: single mutants: hH4 R-F169V, mH4 R-V171F, hH4 R-S179A, hH4 R-S179M; double mutants: hH4 R-F169V+S179A, hH4 R-F169V+S179M and mH4 R-V171F+M181S.

EXPERIMENTAL APPROACH

Site-directed mutagenesis with pVL1392 plasmids containing hH4 or mH4 receptors were performed. Wild-type or mutant receptors were co-expressed with Gαi2 and Gβ1 γ2 in Sf9 cells. Membranes were studied in saturation and competition binding assays ([(3) H]-histamine), and in functional [(35) S]-GTPγS assays with inverse, partial and full agonists of the hH4 receptor.

KEY RESULTS

Constitutive activity decreased from the hH4 receptor via the hH4 R-F169V mutant to the hH4 R-F169V+S179A and hH4 R-F169V+S179M double mutants. F169 alone or in concert with S179 plays a major role in stabilizing a ligand-free active state of the hH4 receptor. Partial inverse hH4 receptor agonists like JNJ7777120 behaved as neutral antagonists or partial agonists at species orthologues with lower or no constitutive activity. Some partial and full hH4 receptor agonists showed decreased maximal effects and potencies at hH4 R-F169V and double mutants. However, the mutation of S179 in the hH4 receptor to M as in mH4 receptor or A as in rH4 receptor did not significantly reduce constitutive activity.

CONCLUSIONS AND IMPLICATIONS

F169 and S179 are key amino acids for the high constitutive activity of hH4 receptors and may also be of relevance for other constitutively active GPCRs.

LINKED ARTICLES

This article is part of a themed issue on Histamine Pharmacology Update published in volume 170 issue 1. To view the other articles in this issue visit http://onlinelibrary.wiley.com/doi/10.1111/bph.2013.170.issue-1/issuetoc.

Increased CD112 expression in methylcholanthrene-induced tumors in CD155-deficient mice

Tumor recognition by immune effector cells is mediated by antigen receptors and a variety of adhesion and costimulatory molecules. The evidence accumulated since the identification of CD155 and CD112 as ligands for DNAM-1 in humans and mice has suggested that the interactions between DNAM-1 and its ligands play an important role in T cell– and natural killer (NK) cell–mediated recognition and lysis of tumor cells. We have previously demonstrated that methylcholanthrane (MCA) accelerates tumor development in DNAM-1–deficient mice, and the Cd155 level on MCA-induced tumors is significantly higher in DNAM-1–deficient mice than in wild-type (WT) mice. By contrast, Cd112 expression on the tumors is similar in WT and DNAM-1-deficient mice, suggesting that CD155 plays a major role as a DNAM-1 ligand in activation of T cells and NK cells for tumor immune surveillance. To address this hypothesis, we examined MCA-induced tumor development in CD155-deficient mice. Unexpectedly, we observed no significant difference in tumor development between WT and CD155-deficient mice. Instead, we found that Cd112 expression was significantly higher in the MCA-induced tumors of CD155-deficient mice than in those of WT mice. We also observed higher expression of DNAM-1 and lower expression of an inhibitory receptor, TIGIT, on CD8⁺ T cells in CD155-deficient mice. These results suggest that modulation of the expression of receptors and CD112 compensates for CD155 deficiency in immune surveillance against MCA-induced tumors.

Poliomyelitis in transgenic mice expressing CD155 under the control of the Tage4 promoter after oral and parenteral poliovirus inoculation

An important step in poliovirus (PV) infection by the oral route in humans is replication of the virus in lymphatic tissues of the gastrointestinal (GI) tract, thought to be mainly in the Peyer's patches of the small intestine. No immunocompetent transgenic (tg) mice that express human PV receptor (CD155) under the control of different promoters can be infected orally. The mouse orthologue of human CD155 is Tage4, a protein expressed at the surface of enterocytes and in the Peyer's patches. We describe here the generation of a tg mouse model in which the Tage4 promoter was used to drive expression of the human PV receptor-coding region (Tage4-CD155tg mice). In this model, CD155 expression was observed by immunostaining in different regions in the Peyer's patches but not in their germinal centres. Although a similar pattern of staining was observed between 3- and 6-week-old Tage4-CD155tg mice, poliomyelitis was only seen in the younger mice after PV infection by the oral route. When compared with TgPVR21 mice that expressed CD155 driven by its human promoter, 3-week-old Tage4-CD155tg mice were more susceptible to gut infection and paralysis following feeding with PV. Also, Tage4-CD155tg mice exhibited higher susceptibility to poliomyelitis after parenteral inoculation of PV. Remarkably, the LD50 after intracerebral inoculation of PV was similar in both CD155 tg mouse strains. The CD155 tg mouse model reported here, although moderately susceptible to oral infection, may be suitable to study mechanisms of PV replication in the gastrointestinal tract and to dissect important aspects of PV neuroinvasiveness.

Lck availability during thymic selection determines the recognition specificity of the T cell repertoire

Thymic selection requires signaling by the protein tyrosine kinase Lck to generate T cells expressing αβ T cell antigen receptors (TCR). For reasons not understood, the thymus selects only αβTCR that are restricted by major histocompatibility complex (MHC)-encoded determinants. Here, we report that Lck proteins that were coreceptor associated promoted thymic selection of conventionally MHC-restricted TCR, but Lck proteins that were coreceptor free promoted thymic selection of MHC-independent TCR. Transgenic TCR with MHC-independent specificity for CD155 utilized coreceptor-free Lck to signal thymic selection in the absence of MHC, unlike any transgenic TCR previously described. Thus, the thymus can select either MHC-restricted or MHC-independent αβTCR depending on whether Lck is coreceptor associated or coreceptor free. We conclude that the intracellular state of Lck determines the specificity of thymic selection and that Lck association with coreceptor proteins during thymic selection is the mechanism by which MHC restriction is imposed on a randomly generated αβTCR repertoire.

On the road to tolerance--generation and migration of gut regulatory T cells

The intestinal immune system potently supports the generation of induced Treg (iTreg) cells. Within intestinal lymphoid compartments iTreg cells receive homing cues, which direct these cells to the gut lamina propria where they expand and locally suppress immune responses. Yet iTreg cells are but one side of a coin, the other side of which comprises natural Treg (nTreg) cells generated in the thymus. nTreg cells, which act in concert with iTreg cells, also acquire a diversified pattern of homing receptors. Thus iTreg and nTreg cells can enter the gut, and draining lymph nodes to cooperatively ensure intestinal homeostasis.

αβ T cell receptors that do not undergo major histocompatibility complex-specific thymic selection possess antibody-like recognition specificities

Major histocompatibility complex (MHC) restriction is the cardinal feature of T cell antigen recognition and is thought to be intrinsic to αβ T cell receptor (TCR) structure because of germline-encoded residues that impose MHC specificity. Here, we analyzed αβTCRs from T cells that had not undergone MHC-specific thymic selection. Instead of recognizing peptide-MHC complexes, the two αβTCRs studied here resembled antibodies in recognizing glycosylation-dependent conformational epitopes on a native self-protein, CD155, and they did so with high affinity independently of MHC molecules. Ligand recognition was via the αβTCR combining site and involved the identical germline-encoded residues that have been thought to uniquely impose MHC specificity, demonstrating that these residues do not only promote MHC binding. This study demonstrates that, without MHC-specific thymic selection, αβTCRs can resemble antibodies in recognizing conformational epitopes on MHC-independent ligands.

IRF-1 expression is essential for natural killer cells to suppress metastasis

IFN-γ promotes tumoral immune surveillance, but its involvement in controlling metastases is less clear. Using a mouse model of pulmonary metastases, we show that local IFN-γ treatment inhibits formation of metastases through its regulation of IRF-1 in tumor cells. IRF-1 is an IFN-γ-induced transcription factor pivotal in the regulation of infection and inflammation. IRF-1 blockade abolished the inhibitory effect of IFN-γ on tumor metastases, whereas ectopic expression of IRF-1 phenocopied the inhibitory effects of IFN-γ. IRF-1 did not affect the survival of tumor cells in the circulation or their infiltration into lungs, but it was essential to support the pulmonary attraction and activation of natural killer (NK) cells. Depleting NK cells from mice abolished the protective effect of IFN-γ or IRF-1 on metastases. In addition, cytotoxicity assays revealed that tumor cells expressing IRF-1 were targeted more effectively by NK cells than IRF-1 nonexpressing tumor cells. Moreover, NK cells isolated from lungs inoculated with IRF-1-expressing tumor cells exhibit a greater cytotoxic activity. Mechanistic investigations revealed that IRF-1-induced NK cell cytotoxicity was independent of perforin and granzyme B but dependent on the NK cell activating receptor DNAM-1. Taken together, our findings establish IRF-1 as an essential mediator of the cross-talk between tumor cells and NK cells that mediate immune surveillance in the metastatic niche.

Intranodal interaction with dendritic cells dynamically regulates surface expression of the co-stimulatory receptor CD226 protein on murine T cells

Dendritic cells (DCs) are the most potent antigen-presenting cells of the immune system. Depending on their maturation status, they prime T cells to induce adaptive immunity or tolerance. DCs express CD155, an immunoglobulin-like receptor binding CD226 present on T and natural killer (NK) cells. CD226 represents an important co-stimulator during T cell priming but also serves as an activating receptor on cytotoxic T and NK cells. Here, we report that cells of the T and NK cell lineage of CD155(-/-) mice express markedly elevated protein levels of CD226 compared with wild type (WT). On heterozygous CD155(+/-) T cells, CD226 up-regulation is half-maximal, implying an inverse gene-dosis effect. Moreover, CD226 up-regulation is independent of antigen-driven activation because it occurs already in thymocytes and naïve peripheral T cells. In vivo, neutralizing anti-CD155 antibody elicits up-regulation of CD226 on T cells demonstrating, that the observed modulation can be triggered by interrupting CD155-CD226 contacts. Adoptive transfers of WT or CD155(-/-) T cells into CD155(-/-) or WT recipients, respectively, revealed that CD226 modulation is accomplished in trans. Analysis of bone marrow chimeras showed that regulators in trans are of hematopoietic origin. We demonstrate that DCs are capable of manipulating CD226 levels on T cells in vivo but not in vitro, suggesting that the process of T cells actively scanning antigen-presenting DCs inside secondary lymphoid organs is required for CD226 modulation. Hence, a CD226 level divergent from WT may be exploited as a sensor to detect abnormal DC/T-cell cross-talk as illustrated for T cells in mice lacking CCR7.

The puzzle of intestinal lamina propria dendritic cells and macrophages

A specialized network of immune cells is positioned directly in the mucosa of the intestinal tract. In this Viewpoint, we discuss the nature and function of DC and macrophages occupying the intestinal lamina propria of mice. DC and macrophages share phenotypic traits and functional plasticity, properties that preclude simple classification of the two cell types. Nevertheless, the information available appears to have reached "critical mass" to allow for a clear demarcation between intestinal macrophages and DC.

The origin and maturity of dendritic cells determine the pattern of sphingosine 1-phosphate receptors expressed and required for efficient migration

Dendritic cells (DCs) represent the most potent inducers of adaptive immune responses. Depending on their activation phenotype, DCs drive naive T cells into distinct differentiation pathways. To achieve this, DCs are present in virtually all tissues where they sample Ag and migrate to the T cell areas of lymph nodes (LNs) and spleen. Ample evidence exists demonstrating that sphingosine 1-phosphate (S1P) is an important modulator of these processes, exerting its effects by binding to the S1P receptor S1P(1) and/or S1P(3). However, published data are contradictory, in part. We show in this study that the expression pattern, as well as the regulation of the S1P receptors, differs among in vitro-generated DCs experiencing different kinds and duration of stimuli. Moreover, the influence of S1P(1) and S1P(3) on the in vivo migration of maturing DCs depends on the origin of these cells. Thus, in vitro-generated DCs require S1P(1) and S1P(3) to accomplish this, whereas skin-derived DCs migrate unhindered in the absence of S1P(3) but not when S1P(1) signaling is blocked. Migration of lamina propria DCs to the mesenteric LNs depends on S1P(1) and S1P(3). In contrast, relocation of maturing spleen-resident DCs to the T cell zone is independent of S1P(1) and S1P(3). However, intrasplenic positioning of immature DCs to the bridging channels depends on S1P(1) activity, with no noticeable contribution of S1P(3). These observations reveal a tissue-dependent contribution of S1P(3) to DC migration and suggest a fundamental role for S1P(1) for maturing DCs migrating from periphery to draining LNs.

Development and functional specialization of CD103+ dendritic cells

CD103 (alpha(E)) integrin expression distinguishes a population of dendritic cells (DCs) that can be found in many if not all lymphoid and non-lymphoid organs. CD103(+) DCs display distinct functional activities. Migratory CD103(+) DCs derived from skin, lung, and intestine efficiently present exogenous antigens in their corresponding draining lymph nodes to specific CD8(+) T cells through a mechanism known as cross-presentation. On the T cells they prime, intestinal CD103(+) DCs can drive the induction of the chemokine receptor CCR9 and alpha(4)beta(7) integrin, both known as gut-homing receptors. CD103(+) DCs also contribute to control inflammatory responses and intestinal homeostasis by fostering the conversion of naive T cells into induced Foxp3(+) regulatory T cells, a mechanism that relies on transforming growth factor-beta and retinoic acid signaling. This review discusses recent findings that identify murine CD103(+) DCs as important regulators of the immune response.

CD155 is involved in negative selection and is required to retain terminally maturing CD8 T cells in thymus

During their final maturation in the medulla, semimature single-positive (SP) thymocytes downregulate activation markers and subsequently exit into the periphery. Although semimature CD4(+) SP cells are sensitive to negative selection, the timing of when negative selection occurs in the CD8 lineage remains elusive. We show that the abundance of terminally matured CD8(+) SP cells in adult thymus is modulated by the genetic background. Moreover, in BALB/c mice, the frequency of terminally matured CD8(+) SP cells, but not that of CD4(+) SP cells present in thymus, varies depending on age. In mice lacking expression of the adhesion receptor CD155, a selective deficiency of mature CD8(+) SP thymocytes was observed, emerging first in adolescent animals at the age when these cells start to accumulate in wild-type thymus. Evidence is provided that the mature cells emigrate prematurely when CD155 is absent, cutting short their retention time in the medulla. Moreover, in nonmanipulated wild-type mice, semimature CD8(+) SP thymocytes are subjected to negative selection, as reflected by the diverging TCR repertoires present on semimature and mature CD8(+) T cells. In CD155-deficient animals, a shift was found in the TCR repertoire displayed by the pool of CD8(+) SP cells, demonstrating that CD155 is involved in negative selection.

Mesenteric lymph node stroma cells in the generation of intestinal immune responses

Lymph nodes at different anatomical locations share similar architecture and operate on the basis of identical principles. Still, the quality of immune responses is modified substantially by the local peculiarities at the site of its induction. Here, we discuss how lymph node stroma cells contribute to functional differences between various lymph nodes, thus helping to explain why and how an immune response induced in skin draining peripheral lymph nodes differs from that elicited in the gut draining mesenteric lymph nodes. Stroma cells constitute a major part of the lymph node scaffold and control the flow of immune cells as well as soluble substances within the organ. Moreover, stroma cells express cytokines, chemokines as well as adhesion factors and thereby actively influence immune status. Lymph node transplantations and adoptive transfers of dendritic cells demonstrated that regional lymph node stroma cells differ in their ability to support mucosal tolerance, the induction of tissue tropism, and humoral immunity. This suggests that stroma cells shape tissue-specific immune responses and equip lymph nodes with unique functional properties that might originate during lymph node organogenesis.

Heterogeneous expression of the adhesion receptor CD226 on murine NK and T cells and its function in NK-mediated killing of immature dendritic cells

The adhesion receptor CD226 (DNAM-1) is a member of the Ig superfamily possessing two extracellular V-like domains. In humans, CD226 was shown to be expressed by NK as well as T cells. During T cell priming, CD226-mediated costimulatory signals may skew the subsequent differentiation into the Th1 pathway. In addition, CD226 expressed on NK and cytotoxic T cells is engaged by its counter-receptor CD155, present on target cells, thereby triggering their elimination. We established mAb specifically recognizing mCD226, demonstrating that CD226 is expressed by precursor and mature but not developing T cells. In contrast, NK cells are distinguished by a rather heterogeneous CD226 expression profile. In addition, expression of CD226 appears coupled to that of other NK cell receptors, as high expression of CD226 was found to correlate with decreased proportions of Ly49D and H positive NK cells. Upon injection into mice, the anti-CD226 antibodies caused selective depletion of CD8(+) T cells. Moreover, these antibodies as well as a naturally occurring CD226 splice variant lacking the outermost V-like domain were instrumental in determining that CD226 adheres to CD155 via its first domain. In addition, antibodies were identified as capable of blocking the CD226/CD155 interaction and to prevent NK-driven killing of immature DC. CD226 is thus the first mNK receptor identified to be essential for the elimination of this particular cell type.

CD96 interaction with CD155 via its first Ig-like domain is modulated by alternative splicing or mutations in distal Ig-like domains

The adhesion receptor CD96 (TACTILE) is a transmembrane glycoprotein possessing three extracellular immunoglobulin-like domains. Among peripheral blood cells, CD96 is expressed on T cells as well as NK cells and a subpopulation of B cells. A possible function of this receptor in NK cell-mediated killing activities was suggested recently. Moreover, CD96 was described as a tumor marker for T-cell acute lymphoblastic leukemia and acute myeloid leukemia. CD96 binds to CD155 (poliovirus receptor) and nectin-1, an adhesion receptor related to CD155. Here we report that human but not mouse CD96 is expressed in two splice variants possessing either an I-like (variant 1) or V-like (variant 2) second domain. With the notable exception of an AML tumor sample, variant 2 predominates in all the CD96-expressing cell types and tissues examined. Using chimeric human/murine CD96 receptors, we show that the interaction with its ligands is mediated via the outermost V-like domain. In contrast to mouse, however, the binding of human CD96 to CD155 is sensitive to the characteristics of the two downstream domains. This is illustrated by a significantly weaker CD96/CD155 interaction mediated by variant 1 when compared with variant 2. Moreover, recent evidence suggested that mutations in human CD96 correlate with the occurrence of a rare form of trigonocephaly. One such mutation causing a single amino acid exchange in the third domain of human CD96 decreased the capacity of both variants to bind to CD155 considerably, suggesting that a CD96-driven adhesion to CD155 may be crucial in developmental processes.

Homeostatic chemokines in development, plasticity, and functional organization of the intestinal immune system

In the past decade accumulating evidence supported the view that the immune system should be regarded as trust consisting of several branches. In this review, we will first introduce the architectural features comprising the intestinal immune system emphasising its plasticity and subsequently discuss the concepts describing its development. We then focus on the chemokine/receptor system as a key integrator managing coordinated migration of and communication among the cells mediating intestinal immunity. Thus, chemokines control development and maintain functionality of the intestinal immune system that is required to perform the unique balancing act between tolerating food, curtailing commensals activities and eliminating pathogenic infections.