Breakdown Of Immune Tolerance Research Articles

Viewing Autoimmune Pathogenesis from the Perspective of Antigen Processing and Determinant Hierarchy.

Autoimmunity results from the breakdown of immune tolerance to defined target self antigens. Like any foreign antigen, a self antigen is continuously processed by antigen-presenting cells (APCs) and its epitopes are displayed by the major histocompatibility complex on the cell surface (dominant epitopes). However, this self antigen fails to induce a T cell response as the T cells against its dominant epitopes have been purged in the thymus during negative selection. In contrast, the T cells against poorly processed (cryptic) self epitopes escape tolerance induction in the thymus and make it to the periphery. Such T cells are generally harmless as their cognate epitopes in the periphery are not presented efficiently. But, under conditions of inflammation and immune activation, previously cryptic epitopes can be revealed on the APC surface for activation of ambient T cells. This can initiate autoimmunity in individuals who are susceptible owing to their genetic and environmental constellation. Subsequent waves of enhanced processing of other epitopes on the same or different self antigens then cause "diversification" or "spreading" of the initial T cell response, resulting in propagation of autoimmunity. However, depending on the disease process and the self antigen involved, "epitope spreading" may instead contribute to natural regression of autoimmunity. This landmark conceptual framework developed by Eli Sercarz and his team ties together determinant hierarchy, selection of epitope-specific T cells, and the induction/progression of autoimmunity. I am extremely fortunate to have worked with Eli and to have been a part of this fascinating research endeavor.

Pathophysiology of paraneoplastic and autoimmune encephalitis: genes, infections, and checkpoint inhibitors.

Paraneoplastic neurological syndromes (PNSs) are rare complications of systemic cancers that can affect all parts of the central and/or peripheral nervous system. A body of experimental and clinical data has demonstrated that the pathogenesis of PNSs is immune-mediated. Nevertheless, the mechanisms leading to immune tolerance breakdown in these conditions remain to be elucidated. Despite their rarity, PNSs offer a unique perspective to understand the complex interplay between cancer immunity, effect of immune checkpoint inhibitors (ICIs), and mechanisms underlying the attack of neurons in antibody-mediated neurological disorders, with potentially relevant therapeutic implications. In particular, it is reported that ICI treatment can unleash PNSs and that the immunopathological features of PNS-related tumors are distinctive, showing prominent tumor-infiltrating lymphocytes and germinal center reactions. Intriguingly, similar pathological substrates have gained further attention as potential biomarkers of ICI-sensitivity and oncological prognosis. Moreover, the genetic analysis of PNS-associated tumors has revealed specific molecular signatures and mutations in genes encoding onconeural proteins, leading to the production of highly immunogenic neoantigens. Other than PNSs, autoimmune encephalitides (AEs) comprise a recently described group of disorders characterized by prominent neuropsychiatric symptoms, diverse antibody spectrum, and less tight association with cancer. Other triggering factors seem to be involved in AEs. Recent data have shed light on the importance of preceding infections (in particular, herpes simplex virus encephalitis) in inducing neurological autoimmune disorders in susceptible individuals (those with a selective deficiency in the innate immune system). In addition, in some AEs (e.g. LGI1-antibody encephalitis) an association with specific host-related factors [e.g., human leukocyte antigen (HLA)] was clearly demonstrated. We provide herein a comprehensive review of the most recent findings in the field of PNSs and AEs, with particular focus on their triggering factors and immunopathogenesis.

JS1.1 Specific genetic alterations of breast tumors lead to Yo paraneoplastic cerebellar syndromes

Abstract BACKGROUND Paraneoplastic cerebellar degenerations with anti-Yo antibodies (Yo-PCD) are rare syndromes associated with ovarian or breast cancers and caused by an auto-immune response against neuronal antigens expressed by tumor cells. We previously demonstrated in Yo-PCD ovarian cancers an association between massive infiltration of ovarian tumors by activated immune effector cells and recurrent gains and/or mutations of onconeural Yo genes (CDR2L and CDR2), suggesting that such genetic alterations in ovarian tumor cells may trigger immune tolerance breakdown and initiation of the auto-immune reaction against Purkinje cells. MATERIAL AND METHODS We pursued the characterization of Yo-PCD tumors and specifically studied breast cancer by IHC, FISH, CGH array and RNA sequencing analysis of 17 breast Yo-PCD tumors and by comparing their genetic characteristics with 10 sporadic breast tumors and public databases. RESULTS We confirmed that specific genetic alterations were also present in breast cancers associated with Yo-PCD. Moreover, this study provides additional evidence for a role of tumor cell specificities in PCD immunopathology by revealing peculiarities in Yo-PCD breast tumors compared to Yo-PCD ovarian cancer. Indeed, not only the CDR2L Yo gene was amplified in 8/9 breast Yo-PCD cancers but also the Erb2/Her2 gene in 15/16 (both genes are on chromosome 17q). In addition to this original Her2 and Yo antigen amplification confirmed by FISH, we observed an overexpression of these proteins by IHC analysis. These Yo-PCD breast cancers are also all negative for hormone receptors (HR). Thus, Yo-PCD breast tumors seem to belong to the molecularly and clinically distinct class of HR-negative and Her2-enriched breast cancers, which represents less than 10 % of breast cancers in the general population. Transcriptomic analysis confirmed that breast Yo-PCD tumors differ by their expression programs from classical breast cancers molecular subtypes. CONCLUSION Understanding the tumor genetic features leading to the immune breakdown and anti-tumor immune response as well as nervous tissue attack remains challenging and seems to be specific according to the tumor subtypes. Herein, our results suggest that, despite sharing common genetic alterations (copy number variations and mutations affecting Yo genes), the Yo-PCD immunopathogenesis of breast and ovarian cancers differ by involving different tumor-specific molecular pathways.

Bcl11b prevents catastrophic autoimmunity by controlling multiple aspects of a regulatory T cell gene expression program.

Foxp3 and its protein partners establish a regulatory T (Treg) cell transcription profile and promote immunological tolerance. However, molecular features contributing to a Treg-specific gene expression program are still incompletely understood. We find that the transcription factor Bcl11b is a prominent Foxp3 cofactor with multifaceted functions in Treg biology. Optimal genomic recruitment of Foxp3 and Bcl11b is critically interdependent. Genome-wide occupancy studies coupled with gene expression profiling reveal that Bcl11b, in association with Foxp3, is primarily responsible in establishing a Treg-specific gene activation program. Furthermore, Bcl11b restricts misdirected recruitment of Foxp3 to sites, which would otherwise result in an altered Treg transcriptome profile. Consequently, Treg-specific ablation of Bcl11b results in marked breakdown of immune tolerance, leading to aggressive systemic autoimmunity. Our study provides previously underappreciated mechanistic insights into molecular events contributing to basic aspects of Treg function. Furthermore, it establishes a therapeutic target with potential implications in autoimmunity and cancer.

013 NETs generate structured antimicrobial peptide-nucleosome immune complexes with inter-DNA spacings optimal for TLR9 activation

The molecular pathogenesis of psoriasis is characterized in part by breakdown of immune tolerance to self-DNA. Recent work demonstrates that the human antimicrobial peptide (AMP) LL37 overexpressed in psoriasis organizes naked DNA into periodic nanocrystals to potently hyperactivate Toll-like receptor 9 (TLR9) in plasmacytoid dendritic cells (pDCs). Interestingly, a subset of self-DNA in psoriatic lesions remain bound to histones as histone-DNA nucleosome core particles (NCPs) released from neutrophil extracellular traps (NETs). At present, it is unknown how NET components like AMPs interact with NCPs, and whether AMP-NCP complexes form structures compatible with TLR9 activation in psoriasis. Here, we combine synchrotron X-ray scattering, cryo-electron microscopy, and computer simulations to demonstrate that under a broad range of conditions, NCPs stack into columns that present periodically arranged dsDNA ligands like threads on a screw, allowing for optimal interdigitation with clusters of TLR9. Remarkably, simulations and electron microscopy indicate that the superhelical pitch of DNA wrapped around the NCP column relaxes to a value that is well-matched with the steric size of TLR9, which predicts strong immune activation. Taken together, our results suggest that AMPs can remodel the structural organization of nucleosomes from NETs into potent amplifiers of inflammation. Preliminary immune activation experiments will be presented.

Acquired Hemophilia A Associated with Dipeptidyl Peptidase-4 Inhibitors for the Treatment of Type 2 Diabetes Mellitus: A Single-Center Case Series in Japan.

Herein we describe four patients with acquired hemophilia A (AHA) caused by factor VIII (FVIII) inhibitor and histories of dipeptidyl peptidase-4 inhibitor (DPP4-I) treatment for diabetes mellitus (DM). Drug exposure can cause a breakdown of immune tolerance to FVIII associated with CD4 T cells, resulting in the induction of autoantibodies against FVIII. In patient 1 in the present series, FVIII inhibitor disappeared after DPP4-I treatment. The DPP4-I treatment was stopped faster in patient 1 than it was in patient 2, whose FVIII inhibitor titer was higher than patient 1’s. Two patients died: patient 3 due to brain infarction after recurrence associated with the development of sigmoid colon rupture, and patient 4 due to multiple organ failure associated with Clostridium difficile colitis. DPP4-I treatment may create an ideal environment for the induction of new antibodies and AHA onset associated with tumor necrosis factor-α reduction. These are the first reported cases of the potential development and/or prolonging of AHA after DDP4-I treatment for DM, and they suggest possible disease associations.Electronic supplementary materialThe online version of this article (10.1007/s13300-019-0609-3) contains supplementary material, which is available to authorized users.

Gliptin-Associated Bullous Pemphigoid: A Valuable Model of the Mechanism of Breakdown of Immune Tolerance against BP180

The study by Plaquevent etal. strongly supports the recent discovery that the use of gliptins is a risk factor for bullous pemphigoid (BP). However, regarding the phenotype of gliptin-associated BP and the necessity of gliptin withdrawal, clinical data remain scarce. We predict that future studies of gliptin-associated BP will offer valuable information concerning autoimmunity against BP180 and may also shed light on the pathology of autoimmune diseases in general.

Pathophysiology of Autoimmune Thrombocytopenia: Current Insight with a Focus on Thrombopoiesis.

Immune thrombocytopenia (ITP) is an autoimmune disease characterized by a significant reduction in the number of circulating platelets which is frequently associated with bleeding. The total count of platelets in the body is finely regulated by the balance between platelet production and destruction. Although the pathogenesis of ITP is still not completely elucidated, it is largely recognized that the low platelet count observed in ITP patients is due to alterations of both mechanisms. An abnormal proliferation of autoreactive T cells leading to the breakdown of immune tolerance to platelet antigens is suggested to be responsible for the up-regulated proliferation of autoantibody producing B cells. Consequently, the immune response induces enhanced T cell-mediated cytotoxicity and antibody-mediated platelet destruction through phagocytosis, complement activation and apoptosis. An additional contribution to the pathophysiology of ITP is given by alterations of thrombopoiesis caused by platelet-reactive autoantibodies or cytotoxic T cells leading to impaired megakaryocyte differentiation and platelet production. All these processes involved in ITP pathophysiology account for the complexity and heterogeneity in the clinical manifestation and therapy responsiveness of this disorder. For this reason, a better understanding of the different underlying mechanisms in ITP is necessary to develop more efficient therapeutic treatments in the future. In this review, we will provide an update on the pathophysiology of ITP with a particular focus on the impact of impaired thrombopoiesis.

Mesenchymal stem cells improve platelet counts in mice with immune thrombocytopenia.

Immune thrombocytopenia (ITP) is a common autoimmune bleeding disorder. The breakdown of immune tolerance (regulatory T [Treg] cells and suppressor cytokines) plays an important role in ITP pathophysiology, especially in refractory ITP. Bone marrow-derived mesenchymal stem cells (BM-MSCs) show immunomodulatory properties and have been extensively utilized for autoimmune diseases. However, it has not been fully elucidated how BM-MSCs affect ITP. In this study, we explore the therapeutic mechanism of BM-MSCs on ITP in mice. Dose-escalation passive ITP mice were inducted by injection of MWReg30. BALB/c mice were randomly divided into two groups: ITP with BM-MSC transplantation and ITP controls. The serum levels of cytokines (interleukin 10 [IL-10] and transforming growth factor-β1 [TGF-β1]) were examined by enzyme-linked immunosorbent assays. The frequency of Treg cells in both peripheral blood and spleen mononuclear cells was analyzed by flow cytometry, and the forkhead box P3 (Foxp3) messenger RNA (mRNA) level was measured by real-time polymerase chain reaction. After BM-MSC treatment, the platelet (PLT) counts were significantly elevated. Meanwhile, cytokines (TGF-β1 and IL-10), the ratios of Treg cells, and the Foxp3 mRNA expression level were significantly higher in the BM-MSC group. Our results show that BM-MSCs can improve PLT counts mainly by secreting suppressive cytokines and upregulating Tregs, which may provide new therapeutic potential for human ITP.

Time-delayed model of autoimmune dynamics.

Among various environmental factors associated with triggering or exacerbating autoimmune response, an important role is played by infections. A breakdown of immune tolerance as a byproduct of immune response against these infections is one of the major causes of autoimmune disease. In this paper we analyse the dynamics of immune response with particular emphasis on the role of time delays characterising the infection and the immune response, as well as on interactions between different types of T cells and cytokines that mediate their behaviour. Stability analysis of the model provides insights into how different model parameters affect the dynamics. Numerical stability analysis and simulations are performed to identify basins of attraction of different dynamical states, and to illustrate the behaviour of the model in different regimes.

Genetic Versus Non-genetic Drivers of SLE: Implications of IRF5 Dysregulation in Both Roads Leading to SLE.

Systemic lupus erythematosus (SLE) is characterized by a breakdown of immune tolerance, resulting in inflammation and tissue destruction. While the primary causes of SLE are still obscure, the disorder is highly heritable. Genetic risk variants, on their own, are rarely causal or fully explain disease pathogenesis. We discuss the possibility that IRF5, a SLE susceptibility gene, has both genetic and non-genetic contributions to disease pathogenesis. Genetic variants within and around IRF5 robustly associate with SLE risk. In SLE blood cells, IRF5 risk variants associate with elevated IRF5 expression and IFN production. Whether the observed increase in expression is due to risk variants or other disease-associated factors is not clear. Data from Irf5-/- mice backcrossed to multiple models of murine lupus support that IRF5's role in disease pathogenesis is non-genetic. Studies of IRF5 expression and function in genotyped healthy donors will address the question of whether IRF5 dysregulation in SLE is driven by genetic or non-genetic factors.

Frequency of bovine viral diarrhea virus detected in subpopulations of peripheral blood mononuclear cells in persistently infected animals and health outcome

Bovine viral diarrhea viruses (BVDV) cause acute and persistent infections. Acute infection results in generalized immunosuppression characterized by a decrease in circulating lymphocytes as a result of depletion of CD4+ and CD8 + T cell populations. Persistent infection with BVDV is the result of immune tolerance and is generally not associated with lymphocytopenia. The health outcome of persistently infected (PI) calves varies widely; some die of mucosal disease, some succumb to ill thrift and others appear normal and survive to adulthood. Detection of BVDV at the single lymphoid cell level is important to the study of subpopulations of peripheral blood mononuclear cells (PBMC) during BVDV infections, however there are few methods available for the detection and quantification of BVDV at this level. To circumvent this difficulty, a novel flow cytometry-based PrimeFlow RNA assay using in-situ detection of BVDV was developed. This assay was used to evaluate differences in viral distribution within subpopulations of PBMC over time in PI calves carrying one of two different species of BVDV (type 1 and type 2). Calves were sampled at 3 different time points approximately one month apart. During the course of the study, a subset of the calves died from ill thrift. Mucosal disease was not indicated in any of the deaths. Using RNA probes specific for the BVDV Npro-Erns coding regions for each respective virus, BVDV RNA was detected in all PBMC of PI that appeared clinically healthy. Calves that succumbed to ill thrift were found to have no or little virus in T cells. The clearance of virus from T cells suggests a breakdown in immune tolerance in these calves. This is the first report of a pattern observed in the viral load in the T cell subpopulations and survival in PI calves.

The Immunogenetic Conundrum of Preeclampsia.

Pregnancy is an immunological challenge to the mother. The fetal tissues including the placenta must be protected from activation of the maternal immune system. On the other hand, the placental tissue sheds into the maternal circulation and must be adequately identified and phagocytized by the maternal immune system. During a healthy pregnancy, numerous immunosuppressive processes take place that allow the allograft fetus to thrive under exposure to humoral and cellular components of the maternal immune system. Breakdown of immune tolerance may result in sterile inflammation and cause adverse pregnancy outcomes such as preeclampsia, a vascular disease of the pregnancy with unpredictable course and symptoms from several organs. Immunological incompatibility between mother and fetus is strongly indicated in preeclampsia. Recently, genetic factors linking immunological pathways to predisposition to preeclampsia have been identified. In this mini-review genetic variation in immunological factors are discussed in the context of preeclampsia. Specifically, we explore immunogenetic and immunomodulary mechanisms contributing to loss of tolerance, inflammation, and autoimmunity in preeclampsia.

The pathogenesis of thyroid autoimmune diseases: New T lymphocytes – Cytokines circuits beyond the Th1−Th2 paradigm

Autoimmune thyroid disease (AITD) is one of the most common organ-specific autoimmune disorders. It mainly manifests as Hashimoto's thyroiditis (HT) and Graves' disease (GD). HT is characteristic of hypothyroidism resulting from the destruction of the thyroid while GD is characteristic of hyperthyroidism due to excessive production of thyroid hormone induced by thyrotropin receptor-specific stimulatory autoantibodies. T lymphocytes and their secretory cytokines play indispensable roles in modulating immune responses, but their roles are often complex and full of interactions among distinct components of the immune system. Dysfunction of these T cells or aberrant expressions of these cytokines can cause the breakdown of immune tolerance and result in aberrant immune responses during the development of AITDs. This review summarizes recently identified T subsets and related cytokines and their roles in the pathogenesis of AITDs with the hope to provide a better understanding of the precise roles of notably identified T subsets in AITDs and facilitate the discovery of functional molecules or novel immune therapeutic targets for AITDs.

Cytokines and Inflammatory Mediators in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterised by a breakdown in immune tolerance that induces an attack on normal tissues by the immune system. The dysfunction within both the innate and adaptive immune systems increases cytokine production, B lymphocytic overproduction of autoantibodies, and T lymphocyte activity. Cytokines and inflammatory mediators have been associated with several clinical endpoints, including the activity of disease and outcomes. In fact, some of them have been associated with different clinical subphenotypes (e.g., lupus nephritis), suggesting their role as biomarkers, and, in some cases, therapeutic targets. Thus, knowledge of the pathophysiological processes associated with the development of SLE could aid in setting up better diagnostic and therapeutic approaches to reduce the high burden of disease, and thus improve quality of life and outcomes. Herein, the authors have compiled a concise review of the clinically relevant cytokines and inflammatory mediators associated with SLE and its manifestations.

The autoimmune ecology: an update.

The autoimmune ecology refers to the interactions between individuals and their environment leading to a breakdown in immune tolerance and, therefore, to the development of one or more autoimmune diseases in such an individual. Herein, an update is offered on four specific factors associated with autoimmune diseases, namely, vitamin D, smoking, alcohol and coffee consumption from the perspective of exposome and metabolomics. Smoking is associated with an increased risk for most of the autoimmune diseases. Carbamylation of proteins as well as NETosis have emerged as possible new pathophysiological mechanisms for rheumatoid arthritis. Low-to-moderate alcohol consumption seems to decrease the risk of systemic lupus erythematosus and rheumatoid arthritis, and studies of vitamin have suggested a beneficial effect on these conditions. Coffee intake appears to be a risk factor for type 1 diabetes mellitus and rheumatoid arthritis and a protective factor for multiple sclerosis and primary biliary cholangitis. Recent studies support the previously established positive associations between environmental factors and most of the autoimmune diseases. Nevertheless, further studies from the perspective of metabolomics, proteomics and genomics will help to clarify the effect of environment on autoimmune diseases.

TLR4+CXCR4+ plasma cells drive nephritis development in systemic lupus erythematosus

ObjectivesIn patients with systemic lupus erythematosus (SLE), immune tolerance breakdown leads to autoantibody production and immune-complex glomerulonephritis. This study aimed to identify pathogenic plasma cells (PC) in the development of...

Increased Susceptibility to Allergic Asthma with the Impairment of Respiratory Tolerance Caused by Psychological Stress

Background: Bronchial asthma is characterized by type 2 T helper (Th2) cell inflammation, essentially due to a breakdown of immune tolerance to harmless environmental allergens. Etiologically, experiences of psychological stress can be associated with a heightened prevalence of asthma. However, the mechanisms underlying stress-related asthma development are unclear. In this study, we examined whether psychological stress increases susceptibility to allergic asthma by downregulating immune tolerance. Methods: Female BALB/c mice were sensitized with ovalbumin/alum, followed by ovalbumin inhalation. Ovalbumin inhalation induced immune tolerance before sensitization occurred. Some mice were exposed to restraint stress during tolerance induction or sensitization. Asthma development was evaluated by airway responsiveness, inflammation, cytokine expression, and IgE synthesis. Sensitization was evaluated by measuring proliferation and cytokine production by splenocytes. The effects of stress exposure on the numbers and functions of dendritic cells and regulatory T (Treg) cells in bronchial lymph nodes and spleens were evaluated. To investigate the role of endogenous glucocorticoid in inhibiting immune tolerance after stress exposure, we examined the effects of (i) a glucocorticoid-receptor antagonist administered prior to stress exposure, and (ii) exogenous gluco­corticoid (instead of stress exposure). Results: Asthmatic responses and Th2-biased sensitization, which were suppressed in tolerized mice, re-emerged in tolerized mice stressed during tolerance induction in association with decreased tolerogenic dendritic and Treg cell numbers. The effects of stress exposure on tolerized mice were abolished by administering a glucocorticoid-receptor antagonist and reproduced by administering exogenous glucocorticoid without stress. Conclusions: Our findings suggested that psychological stress can potentially increase allergic asthma susceptibility by inhibiting immune tolerance.

Aberrant T Cell Signaling and Subsets in Systemic Lupus Erythematosus.

Systemic lupus erythematosus (SLE) is a chronic multi-organ debilitating autoimmune disease, which mainly afflicts women in the reproductive years. A complex interaction of genetics, environmental factors and hormones result in the breakdown of immune tolerance to “self” leading to damage and destruction of multiple organs, such as the skin, joints, kidneys, heart and brain. Both innate and adaptive immune systems are critically involved in the misguided immune response against self-antigens. Dendritic cells, neutrophils, and innate lymphoid cells are important in initiating antigen presentation and propagating inflammation at lymphoid and peripheral tissue sites. Autoantibodies produced by B lymphocytes and immune complex deposition in vital organs contribute to tissue damage. T lymphocytes are increasingly being recognized as key contributors to disease pathogenesis. CD4 T follicular helper cells enable autoantibody production, inflammatory Th17 subsets promote inflammation, while defects in regulatory T cells lead to unchecked immune responses. A better understanding of the molecular defects including signaling events and gene regulation underlying the dysfunctional T cells in SLE is necessary to pave the path for better management, therapy, and perhaps prevention of this complex disease. In this review, we focus on the aberrations in T cell signaling in SLE and highlight therapeutic advances in this field.

Association between bovine viral diarrhea virus load in subsets of peripheral blood mononuclear cells (PBMC) in persistently infected animals and health outcome

Abstract Bovine viral diarrhea virus (BVDV) can cause acute and persistent infections. BVDV acute infection results in generalized immunosuppression characterized by lymphocytopenia typically associated with depletion of CD4+ and CD8+ T cells. BVDV persistent infection is the result of immune tolerance and is not associated with lymphocytopenia. The health outcome of persistently infected (PI) calves varies widely; some die of mucosal disease, some succumb to ill thrift and others survive to adulthood. Detection of BVDV at the single lymphoid cell level is important to the study of subsets of PBMC in acute and persistent infections, however there are few methods available for the detection and quantification of BVDV at the single cell level. To circumvent this difficulty, a novel PrimeFlow RNA assay using in-situ detection of BVDV was developed. This assay was used to evaluate differences in viral distribution within subsets of PBMC over time in PI calves carrying one of two different species of BVDV (type 1 and type 2). Calves were sampled at 3 different time points at least one month apart. During the course of the study, a subset of the calves died from ill thrift. Mucosal disease was not indicated in any of the deaths. Using RNA probes specific for the BVDV Npro-Erns coding region for each respective virus, BVDV RNA was detected in all PBMC of PI that appeared clinically healthy. Calves that succumbed to ill thrift were found to have no or little virus in T cells. The clearance of virus from T cells suggests a breakdown in immune tolerance in these calves. This is the first report of an association between viral load in the T cell populations and survival in PI calves.