Chronic infection of Toxoplasma gondii downregulates miR-132 expression in multiple brain regions in a sex-dependent manner

Elevated matrix Metalloproteinase-9 associated with reduced cerebellar perineuronal nets in female mice with toxoplasmosis

Brain infection by the parasite Toxoplasma gondii is thought to impair learning and memory, although the underlying mechanisms remain largely unknown. Recent studies suggest that perineuronal nets (PNNs) and their key regulator, matrix metalloproteinase-9 (MMP-9), have essential roles in synaptic plasticity associated with learning and memory. We investigated their roles in a chronic toxoplasmosis model using female mice. In mice with a high parasite burden of chronic infection, we found that MMP-9 expression was increased in the peripheral circulation and the brain. A correlation was found between the serum levels of MMP-9 and antibodies to the Toxoplasma matrix antigen MAG1, a surrogate marker for Toxoplasma tissue cysts in the brain. MMP-9 elevation was accompanied by increased expression of its endogenous regulators, TIMP-1 and NGAL. An increase in the levels of GSK-3α/β was observed, alongside a decrease in inhibitory GSK-3α/β (Ser-21/Ser-9) phosphorylation. MMP-9 expression was notably associated with the loss of PNNs but increased expression of the synaptic vesicle protein synaptophysin. There was a trend toward a negative correlation between MMP-9 and aggrecan expression, a critical PNN component. Together, these results suggest that chronic Toxoplasma infection can cause an increase in MMP-9 expression, resulting in the degradation of PNNs, which provides a possible mechanism for Toxoplasma-associated deficits in learning and memory.

A Systematic Review of Apicomplexa Looking into Epigenetic Pathways and the Opportunity for Novel Therapies

Interest in host epigenetic changes during apicomplexan infections increased in the last decade, mainly due to the emergence of new therapies directed to these alterations. This review aims to carry out a bibliometric analysis of the publications related to host epigenetic changes during apicomplexan infections and to summarize the main studied pathways in this context, pointing out those that represent putative drug targets. We used four databases for the article search. After screening, 116 studies were included. The bibliometric analysis revealed that the USA and China had the highest number of relevant publications. The evaluation of the selected studies revealed that Toxoplasma gondii was considered in most of the studies, non-coding RNA was the most frequently reported epigenetic event, and host defense was the most explored pathway. These findings were reinforced by an analysis of the co-occurrence of keywords. Even though we present putative targets for repurposing epidrugs and ncRNA-based drugs in apicomplexan infections, we understand that more detailed knowledge of the hosts' epigenetic pathways is still needed before establishing a definitive drug target.

Behavioral Changes Induced by Latent Toxoplasmosis Could Arise from CNS Inflammation and Neuropathogenesis

Chronic infection with Toxoplasma gondii, a neurotropic parasite, has been linked to multiple behavioral changes in rodents and humans. The pathogenic mechanisms underlying these correlations are not known. I discuss here from animal studies the distribution of tissue cysts, the constant immune surveillance, the critical role of cyst burden, and the time-dependent consequences, which I believe are crucial to explaining the behavioral changes. In line with the brain-wide distribution of tissue cysts and chronic neuroinflammation, infected mice displayed a broad range of behavioral phenotypes. Many studies suggest that behavioral changes in mice are directly associated with tissue cyst presence or cyst burden and the host immune response. Cyst burden may not exert direct effects; however, the mechanisms causing behavioral and neuropathological changes are potentially the consequence of cyst burden over time, such as the neuroinflammation required to control the reactivation of tissue cysts. The reduction of neuroinflammation has proven that neuropathogenesis and behavioral abnormalities can be reversed, at least partially, in infected mice. Overall, Toxoplasma-induced behavioral changes are likely to be an indirect consequence of the host immune response in a parasite burden-dependent manner.

Strain-specific pre-existing immunity: A key to understanding the role of chronic Toxoplasma infection in cognition and Alzheimer's diseases?

Toxoplasma exposure can elicit cellular and humoral immune responses. In the case of chronic Toxoplasma infection, these immune responses are long-lasting. Some studies suggest that pre-existing immunity from Toxoplasma infection can shape immune responses and resistance to other pathogens and brain insults later in life. Much evidence has been generated suggesting Toxoplasma infection may contribute to cognitive impairment in the elderly. However, there have also been studies that disagree with the conclusion. Toxoplasma has many strain types, with virulence being the most notable difference. There is also considerable variation in the outcomes following Toxoplasma exposure ranging from resolved to persistent infection. Therefore, the brain microenvironment, particularly cellular constituents, differs based on the infecting strain (virulent versus hypovirulent) and infection stage (resolved versus persistent). Such difference might play a critical role in determining the outcome of the host on subsequent challengings to the brain. The ability of Toxoplasma strains to set up distinct stages for neurodegenerative pathology through varying degrees of virulence provides unique experimental tools for characterizing these pathways.

Toxoplasmosis: Targeting neurotransmitter systems in psychiatric disorders

The most common form of the disease caused by Toxoplasma gondii (T. gondii) is latent toxoplasmosis due to the formation of tissue cysts in various organs, such as the brain. Latent toxoplasmosis is probably a risk factor in the development of some neuropsychiatric disorders. Behavioral changes after infection are caused by the host immune response, manipulation by the parasite, central nervous system (CNS) inflammation, as well as changes in hormonal and neuromodulator relationships. The present review focused on the exact mechanisms of T. gondii effect on the alteration of behavior and neurotransmitter levels, their catabolites and metabolites, as well as the interaction between immune responses and this parasite in the etiopathogenesis of psychiatric disorders. The dysfunction of neurotransmitters in the neural transmission is associated with several neuropsychiatric disorders. However, further intensive studies are required to determine the effect of this parasite on altering the level of neurotransmitters and the role of neurotransmitters in the etiology of host behavioral changes.

Toxoplasma gondii: A possible etiologic agent for Alzheimer's disease

Toxoplasma gondii (T. gondii) is one of the most pervasive neurotropic pathogens causing different lesions in a wide variety of mammals as intermediate hosts, including humans. It is estimated that one-third of the world population is infected with T. gondii; however, for a long time, there has been much interest in the examination of the possible role of this parasite in the development of mental disorders, such as Alzheimer's disease (AD). T. gondii may play a role in the progression of AD using mechanisms, such as the induction of the host's immune responses, inflammation of the central nervous system (CNS), alteration in the levels of neurotransmitters, and activation of indoleamine-2,3-dyoxigenase. This paper presents an appraisal of the literature, reports, and studies that seek to the possible role of T. gondii in the development of AD. For achieving the purpose of the current study, a search of six English databases (PubMed, ScienceDirect, Web of Science, Scopus, ProQuest, and Google Scholar) was performed. The results support the involvement of T. gondii in the induction and development of AD. Indeed, T. gondii can be considered a risk factor for the development of AD and requires the special attention of specialists and patients. Furthermore, the results of this study may contribute to prevent or delay the progress of AD worldwide. Therefore, it is required to carry out further studies in order to better perceive the parasitic mechanisms in the progression of AD.

Toxoplasmosis and Psychiatric and Neurological Disorders: A Step toward Understanding Parasite Pathogenesis

Toxoplasmosis, a disease that disrupts fetal brain development and severely affects the host's brain, has been linked to many behavioral and neurological disorders. There is growing interest in how a single-celled neurotropic parasite, Toxoplasma gondii, can control or change the behavior of the host as well as how it dominates the host's neurons. Secrets beyond these could be answered by decoding the Toxoplasma gondii genome, unravelling the function of genomic sequences, and exploring epigenetics and mRNAs alterations, as well as the postulated mechanisms contributing to various neurological and psychiatric symptoms caused by this parasite. Substantial efforts have been made to elucidate the action of T. gondii on host immunity and the biology of its infection. However, the available studies on the molecular aspects of toxoplasmosis that affect central nervous system (CNS) circuits remain limited, and much research is still needed on this interesting topic. In my opinion, this parasite is a gift for studying the biology of the nervous system and related diseases. We should utilize the unique features of Toxoplasma, such as its abilities to modulate brain physiology, for neurological studies or as a possible tool or approach to cure neurological disease.

Impaired social behaviour and molecular mediators of associated neural circuits during chronic Toxoplasma gondii infection in female mice

Toxoplasma gondii (T. gondii) is a neurotropic parasite that is associated with various neuropsychiatric disorders. Rodents infected with T. gondii display a plethora of behavioural alterations, and Toxoplasma infection in humans has been strongly associated with disorders such as schizophrenia, in which impaired social behaviour is an important feature. Elucidating changes at the cellular level relevant to neuropsychiatric conditions can lead to effective therapies. Here, we compare changes in behaviour during an acute and chronic T. gondii infection in female mice. Further, we notice that during chronic phase of infection, mice display impaired sociability when exposed to a novel conspecific. Also, we show that T. gondii infected mice display impaired short-term social recognition memory. However, object recognition memory remains intact. Using c-Fos as a marker of neuronal activity, we show that infection leads to an impairment in neuronal activation in the medial prefrontal cortex, hippocampus as well as the amygdala when mice are exposed to a social environment and a change in functional connectivity between these regions. We found changes in synaptic proteins that play a role in the process of neuronal activation such as synaptophysin, PSD-95 and changes in downstream substrates of cell activity such as cyclic AMP, phospho-CREB and BDNF. Our results point towards an imbalance in neuronal activity that can lead to a wider range of neuropsychiatric problems upon T. gondii infection.

Altered Expression Levels of MicroRNA-132 and Nurr1 in Peripheral Blood of Parkinson's Disease: Potential Disease Biomarkers

MicroRNAs (miRNAs) are small and evolutionary conserved noncoding RNAs that are involved in post-transcriptional gene regulation. Differential expression levels of miRNAs can be used as potential biomarkers of disease. Previous animal studies have indicated that the expression level of miR-132 is negatively correlated with its downstream molecule nuclear receptor related 1 protein (Nurr1), which is one of the key factors for the maintenance of dopaminergic function and is particularly vulnerable in Parkinson's disease (PD). However, this correlation has not been confirmed in human patients with PD. Moreover, the possible involvement of miR-132 during the pathogenesis and progression of PD is not fully investigated. Therefore, in the present study, we determined the peripheral circulation levels of miR-132 and Nurr1 in patients with PD, neurological disease controls (NDC) and healthy controls (HC) by reverse transcription real-time quantitative PCR (RT-qPCR). Our data clearly demonstrated that the plasma miR-132 level in PD was significantly higher than those in HC (178%, p < 0.05) and NDC (188%, p < 0.001). When adjusted for gender and age, higher level of miR-132 expression was associated with the significantly increased risk for PD in males and was closely related with the disease stages and disease severity. Furthermore, peripheral Nurr1 was significantly decreased in PD compared with HC (56%, p < 0.001) and NDC (58%, p < 0.001). Much more interestingly, further analysis revealed a negative correlation between the decreased Nurr1 level and the elevated miR-132 level in PD. All these findings indicated that the combination of a high miR-132 level with the low level of its downstream Nurr1 might be a potential biomarker aiding in the diagnosis of PD and monitoring disease progression.

Impact of Toxoplasma gondii Infection on Host Non-coding RNA Responses

As an intracellular microbe, Toxoplasma gondii must establish a highly intimate relationship with its host to ensure success as a parasite. Many studies over the last decade-and-a-half have highlighted how the host reshapes its immunoproteome to survive infection, and conversely how the parasite regulates host responses to ensure persistence. The role of host non-protein-coding RNA during infection is a vast and largely unexplored area of emerging interest. The potential importance of this facet of the host-parasite interaction is underscored by current estimates that as much as 80% of the host genome is transcribed into non-translated RNA. Here, we review the current state of knowledge with respect to two major classes of non-coding RNA, microRNA (miRNA) and long non-coding RNA (lncRNA), in the host response to T. gondii infection. These two classes of regulatory RNA are known to have profound and widespread effects on cell function. However, their impact on infection and immunity is not well-understood, particularly for the response to T. gondii. Nevertheless, numerous miRNAs have been identified that are upregulated by Toxoplasma, and emerging evidence suggests a functional role during infection. While the field of lncRNA is in its infancy, it is already clear that Toxoplasma is also a strong trigger for this class of regulatory RNA. Non-coding RNA responses induced by T. gondii are likely to be major determinants of the host's ability to resist infection and the parasite's ability to establish long-term latency.

Toxoplasmosis: A pathway to neuropsychiatric disorders

Toxoplasma gondii is an obligate intracellular parasite that resides, in a latent form, in the human central nervous system. Infection with Toxoplasma drastically alters the behaviour of rodents and is associated with the incidence of specific neuropsychiatric conditions in humans. But the question remains: how does this pervasive human pathogen alter behaviour of the mammalian host? This fundamental question is receiving increasing attention as it has far reaching public health implications for a parasite that is very common in human populations. Our current understanding centres on neuronal changes that are elicited directly by this intracellular parasite versus indirect changes that occur due to activation of the immune system within the CNS, or a combination of both. In this review, we explore the interactions between Toxoplasma and its host, the proposed mechanisms and consequences on neuronal function and mental health, and discuss Toxoplasma infection as a public health issue.

Chronic Toxoplasma gondii Infection Induces Anti-N-Methyl-d-Aspartate Receptor Autoantibodies and Associated Behavioral Changes and Neuropathology

Anti-NMDA receptor (NMDAR) autoantibodies have been postulated to play a role in the pathogenesis of NMDAR hypofunction, which contributes to the etiology of psychotic symptoms. Toxoplasma gondii is a pathogen implicated in psychiatric disorders and associated with elevation of NMDAR autoantibodies. However, it remains unclear whether parasite infection is the cause of NMDAR autoantibodies. By using mouse models, we found that NMDAR autoantibody generation had a strong temporal association with tissue cyst formation, as determined by MAG1 antibody seroreactivity (r = 0.96; P < 0.0001), which is a serologic marker for the cyst burden. The presence of MAG1 antibody response, but not T. gondii IgG response, was required for NMDAR autoantibody production. The pathogenic relevance of NMDAR autoantibodies to behavioral abnormalities (blunted response to amphetamine-triggered activity and decreased locomotor activity and exploration) and reduced expression of synaptic proteins (the GLUN2B subtype of NMDAR and PSD-95) has been demonstrated in infected mice. Our study suggests that NMDAR autoantibodies are specifically induced by persistent T. gondii infection and are most likely triggered by tissue cysts. NMDAR autoantibody seroreactivity may be a novel pathological hallmark of chronic toxoplasmosis, which raises questions about NMDAR hypofunction and neurodegeneration in the infected brain.

miR-20a inhibition using locked nucleic acid (LNA) technology and its effects on apoptosis of human macrophages infected by Toxoplasma gondii RH strain

Toxoplasma gondii is a ubiquitous and infectious parasite that multiplies in any nucleated cell of warm-blooded animals and humans worldwide. This parasite has intricate mechanisms to reciprocate host-cell apoptosis to exist in the host cell. So far, the details of the parasite interactions with host cells are not well known. MicroRNAs (miRNAs) are one of the small noncoding RNAs that are now considered as a key mechanism of gene regulation. They are important in physiological and pathological processes such as apoptosis. In this study a Real Time quantitative PCR technique was used to evaluate the levels of miR-20a of miRNAs family in human macrophage during T. gondii infection to determine the role of miR-20a in apoptosis. Then, the inhibition of miR-20a function through interaction with transfection of Locked Nucleic Acid (LNA) antisense oligomer was studied. Furthermore, it was examined whether miR-20a is involved in apoptosis of human macrophages with T. gondii infected cells using flow cytometry. We found that miR-20a expression is up-regulated in human macrophages following T. gondii infection. After LNA anti miR-20a oligomer transfection, miR-20a inhibition was evaluated by quantitative reverse transcriptase polymerase chain reaction. Flow cytometry results showed that LNA anti-miR20a oligomer increased apoptosis. In agreement with this result, we found that specific LNA oligonucleotides prevent the functional activity of miR-20a and promotion of human macrophages apoptosis with T. gondii infection by inhibition of this miRNAs gene. Also, the results support the concept that LNA oligomer antisense may be used as a therapeutic implement for blocking detrimental miRNAs overexpressed in infections.

Advances in Roles of miR-132 in the Nervous System

miR-132 is an endogenous small RNA and controls post-transcriptional regulation of gene expression via controlled degradation of mRNA or transcription inhibition. In the nervous system, miR-132 is significant for regulating neuronal differentiation, maturation and functioning, and widely participates in axon growth, neural migration, and plasticity. The miR-132 is affected by factors like mRNA expression, functional redundancy, and signaling cascades. It targets multiple downstream molecules to influence physiological and pathological neuronal activities. MiR-132 can influence the pathogenesis of many diseases, especially in the nervous system. The dysregulation of miR-132 results in the occurrence and exacerbation of neural developmental, degenerative diseases, like Alzheimer’s disease, Parkinson’s disease and epilepsy, neural infection and psychiatric disorders including disturbance of consciousness, cognition and memory, depression and schizophrenia. Regulation of miR-132 expression relieves symptoms, alleviates severity and finally effects a cure. This review aims to discuss the clinical potentials of miR-132 in the nervous system.

Effects of genistein and swimming exercise on spatial memory and expression of microRNA 132, BDNF, and IGF-1 genes in the hippocampus of ovariectomized rats

OBJECTIVES

The aim of the present study was to investigate the effects of genistein and exercise on the spatial memory and expression of microRNA-132, BDNF, and IGF-1 in the hippocampus of ovariectomized rats.

MATERIALS AND METHODS

Sixty animals were divided into six groups of control, sham, ovariectomy (OVX), ovariectomized with 8 weeks of genistein administration (OVX.G), with 8 weeks of swimming training (OVX.E), and with 8 weeks of both of them (OVX.G.E). The effect of genistein and/or exercise was evaluated by measuring microRNA-132, BDNF, and IGF-1 expression levels in the hippocampus tissue. Grafts were analyzed using Real-time polymerase chain reaction for microRNA-132, BDNF, IGF-1, and spatial memory via a Morris water maze (MWM).

RESULTS

Our findings showed that ovariectomy decreased the expression of microRNA-132, BDNF, and IGF-1 in the hippocampus (P<0.05) in comparison with the sham group as well as performance in the water maze (P<0.05). Also according to results ovariectomized groups that were treated with genistein/exercise or both of them showed significant difference in expression of microRNA-132, BDNF, and IGF-1 in the hippocampus (P<0.05) and decreased latency in MWM (P<0.05) compared with the OVX group but combination treatment was more effective in the OVX.G.E group in comparison with OVX.E and OVX.G groups.

CONCLUSION

Overall our results emphasized that combination treatment with genistein and exercise could improve microRNA-132, BDNF, and IGF-1 expression in the hippocampus as well as the spatial memory of ovariectomized rats. These effects may have beneficial impacts on the menopausal period.

Neurophysiological Changes Induced by Chronic Toxoplasma gondii Infection

Although the parasite Toxoplasma gondii is one of the most pervasive neurotropic pathogens in the world, the host-parasite interactions during CNS infection and the consequences of neurological infection are just beginning to be unraveled. The chronic stages of infection have been considered dormant, although several studies have found correlations of infection with an array of host behavioral changes. These may facilitate parasite transmission and impact neurological diseases. During infection, in addition to the presence of the parasites within neurons, host-mediated neuroimmune and hormonal responses to infection are also present. T. gondii induces numerous changes to host neurons during infection and globally alters host neurological signaling pathways, as discussed in this review. Understanding the neurophysiological changes in the host brain is imperative to understanding the parasitic mechanisms and to delineate the effects of this single-celled parasite on health and its contribution to neurological disease.

Cytokine profiles in patients with toxoplasmic lymphadenitis in the setting of pregnancy

INTRODUCTION

Majority of Toxoplasma gondii infections are benign and asymptomatic; however, some patients experience toxoplasmic lymphadenitis (TL). Factors associated as to whether infection will be symptomatic or not are unknown.

METHODS

Dye test titers of patients with acute toxoplasmosis (pregnant and not pregnant) with TL (TL+) were compared with those in patients with asymptomatic acute infection (TL-). Additionally, mean levels of 62 serum cytokines were compared between TL+ and TL- pregnant women and between TL+ pregnant and non-pregnant women.

RESULTS

During acute infection, mean dye test titer was higher in TL+ than in TL- patients (p=0.021). In addition, out of 62 cytokines, CXCL9andCXCL10 levels were higher (p<0.05) and resistin mean levels were lower (p<0.05) in pregnant women with TL+ compared to TL-. Among patients with TL+, levels of VCAM1andCCL2 were lower (p<0.05) in pregnant women than in non-pregnant women.

CONCLUSION

Here we report differences in dye test titers in patients with acute infection. Cytokine responses vary according to the presence of TL+ and to the pregnancy status. Factors underlying these differences are presently unknown and require further studies to define individual and combined roles of cytokines in TL+.

Toxoplasma gondii-A Gastrointestinal Pathogen Associated with Human Brain Diseases

Serious psychiatric disorders such as schizophrenia, bipolar disorder, and major depression are important causes of mortality and morbidity worldwide. While these are primarily diseases involving altered brain functioning, numerous studies have documented increased rates of gastrointestinal inflammation and dysfunction in many individuals with these disorders. Toxoplasma gondii is an apicomplexan protozoan intracellular parasite with a widespread distribution in both developed and developing countries. Toxoplasma organisms enter the ecosystem through the shedding of oocysts by Toxoplasma-infected felines. In almost all cases of postnatal human infection, Toxoplasma enters its hosts through the intestinal tract either by the ingestion of oocysts or by the consumption of meat from food animals which themselves were infected by Toxoplasma oocysts. It had previously been thought that most cases of Toxoplasma infection in immune competent children and adults were inapparent and asymptomatic. However, recent studies cast doubt on this concept as exposure to Toxoplasma has been associated with a range of acute and chronic symptoms. Of particular note has been the finding of an increased rate of a range of neurological and psychiatric disorders associated with serological evidence of Toxoplasma exposure. A role of Toxoplasma infection in brain diseases is also supported by the consistent finding of altered cognition and behavior in animal models of infections. Much of the attention relating to the role of Toxoplasma infection in neuropsychiatric disorders has focused on the brain, where Toxoplasma tissue cysts can persist for extended periods of time. However, recent discoveries relating to the role of the gastrointestinal tract in cognition and behavior suggest that Toxoplasma may also increase susceptibility to human brain diseases through immune activation, particularly involving the gastrointestinal mucosa. The study of the pathways relating to the pathobiology and immunology of Toxoplasma infection may provide insights into the pathogenesis of a range of human neuropsychiatric disorders as well as into cognitive functioning in otherwise healthy individuals.

Behavioral Abnormalities in a Mouse Model of Chronic Toxoplasmosis Are Associated with MAG1 Antibody Levels and Cyst Burden

There is marked variation in the human response to Toxoplasma gondii infection. Epidemiological studies indicate associations between strain virulence and severity of toxoplasmosis. Animal studies on the pathogenic effect of chronic infection focused on relatively avirulent strains (e.g. type II) because they can easily establish latent infections in mice, defined by the presence of bradyzoite-containing cysts. To provide insight into virulent strain-related severity of human toxoplasmosis, we established a chronic model of the virulent type I strain using outbred mice. We found that type I-exposed mice displayed variable outcomes ranging from aborted to severe infections. According to antibody profiles, we found that most of mice generated antibodies against T. gondii organism but varied greatly in the production of antibodies against matrix antigen MAG1. There was a strong correlation between MAG1 antibody level and brain cyst burden in chronically infected mice (r = 0.82, p = 0.0021). We found that mice with high MAG1 antibody level displayed lower weight, behavioral changes, altered levels of gene expression and immune activation. The most striking change in behavior we discovered was a blunted response to amphetamine-trigged locomotor activity. The extent of most changes was directly correlated with levels of MAG1 antibody. These changes were not found in mice with less cyst burden or mice that were acutely but not chronically infected. Our finding highlights the critical role of cyst burden in a range of disease severity during chronic infection, the predictive value of MAG1 antibody level to brain cyst burden and to changes in behavior or other pathology in chronically infected mice. Our finding may have important implications for understanding the heterogeneous effects of T. gondii infections in human.

Chronic infection with Toxoplasma gondii, a common neurotropic pathogen, affects approximately 1 billion people worldwide. There is marked variation in the human response to infection. Epidemiological studies indicate that virulent strains of T. gondii are associated with increased frequency and severity of human toxoplasmosis. However, animal studies on the pathogenic effect of chronic infection have focused on relatively avirulent strains because they can easily establish latent infections in mice. Employing a murine model of chronic infection with virulent strain, we found that mice displayed variable outcomes ranging from aborted to severe infections. Parasite burden, as measured serologically, was found to be the critical determinant of behavioral and pathogenic changes in chronically infected mice. This study demonstrated the predictive value of serologically determined parasite burden to the levels of chronic infection. Our finding highlights the critical role of parasite burden in a range of disease severity during chronic infection. Our finding may have important implications for understanding the heterogeneous effects of T. gondii infections in human.