Testosterone and other gonadal factor(s) restrict the efficacy of genes controlling resistance to Plasmodium chabaudi malaria

Effects of gonadectomy on the incidence rate of babesiosis and the risk of severe babesiosis in dogs aged 6 months and older at a veterinary academic hospital in South Africa: A case-control and retrospective cohort study

Gonadectomy in dogs is associated with changes in risks of a variety of non-infectious health conditions, but few studies have examined its effects on infectious disease outcomes. The objectives of our study were to estimate the causal effect of gonadectomy on the incidence rate of babesiosis diagnosis, and on the risk of severe babesiosis in diagnosed cases, in dogs 6 months and older seen at a veterinary academic hospital in South Africa from 2013 through 2020. To estimate the effect of gonadectomy on the incidence rate of babesiosis diagnosis in dogs, we conducted a case-control study with incidence density sampling of dogs seen through the hospital's primary care service, adjusting for sex, age, breed category and weight. We identified 811 cases and selected 3244 time-matched controls. To estimate the effect of gonadectomy on disease severity in dogs with babesiosis, we conducted a retrospective cohort study among all dogs with a diagnosis of babesiosis (n=923), including these 811 cases and a further 112 referred to the hospital, also adjusting for sex, age, breed category and weight. Gonadectomy substantially reduced the incidence rate of babesiosis (total effect incidence rate ratio [IRR] 0.5; 95 % confidence interval [CI] 0.41-0.60) and the risk of severe babesiosis among diagnosed dogs (total effect risk ratio [RR] 0.72; 95 % CI 0.60-0.86). Tipping point sensitivity analysis shows that these effect estimates are robust to unmeasured confounding bias. There was no evidence for modification of the effect of gonadectomy by sex, with effect estimates qualitatively similar for males and females for both outcomes. Compared to females, males had a higher incidence rate of babesiosis (IRR 1.74; 95 % CI 1.49-2.04) and a higher risk of severe disease (RR 1.12; 95 % CI 0.98-1.28). In conclusion, our study shows a robust protective effect of gonadectomy on the incidence and severity of babesiosis in both male and female dogs 6 months of age and older, and contributes important evidence to the debate on the overall risks and benefits of gonadectomy to dogs in this population.

Schoolchildren with asymptomatic malaria are potential hotspot for malaria reservoir in Ethiopia: implications for malaria control and elimination efforts

BACKGROUND

Schoolchildren with asymptomatic malaria infections often go undiagnosed and untreated, serving as reservoirs for infection that hamper malaria control and elimination efforts. In this context, little is known about the magnitude of asymptomatic malaria infections in apparently healthy schoolchildren in Ethiopia. This study was aimed at determining the prevalence of asymptomatic malaria infection and its associated factors in apparently healthy schoolchildren in Ethiopia.

METHODS

From September 2021 to January 2022, a school-based cross-sectional study was conducted on 994 apparently healthy schoolchildren (aged 6-15 years) selected from 21 primary schools in the Gomma district, of Jimma zone, southwestern Oromia, Ethiopia. A multi-stage sampling technique was used to select schools and participants. After allocating the total sample proportionally to each school and then to each grade, participants were selected using the lottery method from a list of student records (rosters). Finger-pricked blood samples were collected for microscopy blood film preparation and malaria rapid diagnostic test (RDT) (SD Bioline Malaria Ag Pf/Pv). Moreover, dry blood spots (DBSs) were prepared onto filter papers for quantitative real time polymerase chain reaction (qPCR) analysis.

RESULTS

As determined by RDT and microscopy, the prevalence of asymptomatic malaria was 2.20% and 1.51%, respectively. Using qPCR, the overall prevalence was 5.03% (50/994). Of this, Plasmodium falciparum, Plasmodium vivax and mixed infections accounted for 90%, 6% and 4%, respectively. Submicroscopic asymptomatic malaria infection was also accounted for 70% (35/50) of the overall prevalence. Household head age, nighttime outdoor activities of household heads, family history of malaria, absence of insecticide-treated nets (ITN), and presence of stagnant water around the houses are all significantly associated with asymptomatic malaria infections among schoolchildren.

CONCLUSIONS

This study found that both RDT and microscopy underestimated the prevalence of asymptomatic malaria in schoolchildren. However, qPCR was able to detect even low levels of parasitaemia and revealed a higher prevalence of asymptomatic submicroscopic malaria infections. The findings imply that schoolchildren with asymptomatic malaria infection are potential hotspot for malaria reservoir that fuels ongoing transmission. Therefore, it is imperative to include schoolchildren and schools in malaria intervention package and equally important is the adoption of more advanced and sensitive diagnostic tools, which would be crucial for successful malaria control and elimination efforts. Targeted interventions for asymptomatic malaria-infected schoolchildren can provide invaluable support to the National Malaria Control Programme in controlling and eventually eliminating the disease.

Immunomodulatory effects of testosterone and letrozole during Plasmodium berghei ANKA infection

Introduction

Malaria is one of the leading health problems globally. Plasmodium infection causes pronounced sexual dimorphism, and the lethality and severity are more remarkable in males than in females. To study the role of testosterone in the susceptibility and mortality of males in malaria, it is common to increase its concentration. However, this strategy does not consider the enzyme CYP19A1 aromatase, which can transform it into oestrogens.

Methods

To avoid the interference of oestrogens, we inhibited in vivo CYP19A1 aromatase with letrozole and increased the testosterone level by exogen administration before infection with Plasmodium berghei ANKA. We measured the impact on free testosterone, 17β-oestradiol and dehydroepiandrosterone levels in plasma; additionally, we evaluated parasitaemia, body temperature, body mass, glucose levels and haemoglobin concentration. Furthermore, we evaluated the effects of testosterone on the immune response; we quantified the CD3+/CD4+, CD3+/CD8+, CD19+, Mac-3+ and NK cells in the spleen and the plasma concentrations of the cytokines IL-2, IL-4, IL-6, IFN-, IL-10, TNF-α and IL-17A. Finally, we quantified the levels of antibodies.

Results

We found that mice treated with the combination of letrozole and testosterone and infected with Plasmodium berghei ANKA had increased concentrations of free testosterone and DHEA but decreased levels of 17β-oestradiol. As a result, parasitaemia increased, leading to severe anaemia. Interestingly, testosterone increased temperature and decreased glucose concentration as a possible testosterone-mediated regulatory mechanism. The severity of symptomatology was related to critical immunomodulatory effects generated by free testosterone; it selectively increased CD3+CD8+ T and CD19+ cells but decreased Mac-3+. Remarkably, it reduced IL-17A concentration and increased IL-4 and TNF-α. Finally, it increased IgG1 levels and the IgG1/IgG2a ratio. In conclusion, free testosterone plays an essential role in pathogenesis in male mice by increasing CD8+ and decreasing Mac3+ cells and mainly reducing IL-17A levels, which is critical in the development of anaemia. Our results are important for understanding the mechanisms that regulate the exacerbated inflammatory response in infectious diseases and would be useful for the future development of alternative therapies to reduce the mortality generated by inflammatory processes.

Sex-Linked Differences in Malaria Risk Across the Lifespan

Despite the high burden of malaria worldwide, there is surprisingly scarce research on sex-based differences in malaria outside of pregnancy. A more thorough understanding of sexual dimorphism in malaria, and what underlies these sex-based differences, could elucidate the underlying mechanisms driving malaria pathogenesis and has the potential to inform malaria control efforts, including new vaccines. This review summarizes our current understanding of sex-based differences in the epidemiology of malaria across the lifespan, potential sex- or gender-based mechanisms driving these differences, and the knowledge gaps that need to be addressed.

Testosterone induces sexual dimorphism during infection with Plasmodium berghei ANKA

Malaria is the most lethal parasitic disease worldwide; men exhibit higher mortality and more severe symptomatology than women; however, in most studies of immune response in malaria, sex is not considered a variable. Sex hormones 17β-oestradiol and testosterone are responsible for the main physiological differences between sexes. When interacting with their receptors on different immune cells, they modify the expression of genes that modulate cell proliferation, differentiation, and synthesis of cytokines. The immunosuppressive activity of testosterone is well accepted; however, its participation in the sexual dimorphism of the immune response to malaria has not been studied. In this work, we analysed whether altering the concentration of testosterone, through increasing the concentration of this hormone for exogenous administration for three weeks, or gonadectomy before infection with Plasmodium berghei ANKA affects different cells of the immune response necessary for parasite clearance. We also assessed the concentration of pro-and anti-inflammatory cytokines in male and female CBA/Ca mice infected or not with the parasite. Our results show that testosterone changes affect females more than males, resulting in sex-associated patterns. Testosterone administration increased parasitaemia in intact males while reducing it in intact females leading to a dimorphic pattern. In addition, gonadectomy increased parasitaemia in both sexes. Moreover, testosterone administration prevented both weight loss caused by the infection in females and hypothermia in gonadectomized mice of both sexes. Boosting testosterone concentration increased CD3+ and CD8+ populations but decreased the B220+ cells exclusively in females. Additionally, testosterone reduced IFN-γ concentration and increased IL-6 levels only in females, while in males, testosterone increased the number of NK cells. Finally, gonadectomy decreased TNF-α concentration in both sexes. Our results demonstrate that testosterone induces different patterns depending on sex and testosterone concentration. The results of this work contribute to understanding the impact of modifying testosterone concentration on the immune response specific against Plasmodium and the participation of this hormone in sexual dimorphism in malaria.

Sex-based differences in clearance of chronic Plasmodium falciparum infection

Multiple studies have reported a male bias in incidence and/or prevalence of malaria infection in males compared to females. To test the hypothesis that sex-based differences in host-parasite interactions affect the epidemiology of malaria, we intensively followed Plasmodium falciparum infections in a cohort in a malaria endemic area of eastern Uganda and estimated both force of infection (FOI) and rate of clearance using amplicon deep-sequencing. We found no evidence of differences in behavioral risk factors, incidence of malaria, or FOI by sex. In contrast, females cleared asymptomatic infections at a faster rate than males (hazard ratio [HR]=1.82, 95% CI 1.20 to 2.75 by clone and HR = 2.07, 95% CI 1.24 to 3.47 by infection event) in multivariate models adjusted for age, timing of infection onset, and parasite density. These findings implicate biological sex-based differences as an important factor in the host response to this globally important pathogen.

Impact of Exogenous Testosterone on Reproduction in Transgender Men

Studies show that a subset of transgender men desire children; however, there is a paucity of literature on the effect of gender-affirming testosterone therapy on reproductive function. In this manuscript, we will review the process of gender-affirming hormone therapy for transgender men and what is known about ovarian and uterine consequences of testosterone exposure in transgender men; draw parallels with existing animal models of androgen exposure; summarize the existing literature on parenting experiences and desires in transgender people; discuss considerations for assisted reproductive technologies and fertility preservation; and identify gaps in the literature and opportunities for further research.

Sex-Associated Differential mRNA Expression of Cytokines and Its Regulation by Sex Steroids in Different Brain Regions in a Plasmodium berghei ANKA Model of Cerebral Malaria

Cerebral malaria (CM) is the major complication associated with death in malaria patients, and its pathogenesis is associated with excessive proinflammatory cytokine production. Notably, the severity and mortality of natural infections with Plasmodium are higher in males than females, suggesting that sexual hormones influence both the pathogenesis of and immune response in CM. However, no studies on inflammation mediators in the brains of both sexes have been reported. In this work, the mRNA expression levels of the proinflammatory cytokines IL-1β, IFN-γ, TNF-α, and IL-2 were measured in the preoptic area, hypothalamus, hippocampus, olfactory bulb, frontal cortex, and lateral cortex regions of gonadectomized female and male CBA/Ca mice infected with P. berghei ANKA (a recognized experimental CM model). Our findings demonstrate that both infection with P. berghei ANKA and gonadectomy trigger a cerebral sex dimorphic mRNA expression pattern of the cytokines IL-1β, TNF-α, IFN-γ, and IL-2. This dimorphic cytokine pattern was different in each brain region analysed. In most cases, infected males exhibited higher mRNA expression levels than females, suggesting that sexual hormones differentially regulate the mRNA expression of proinflammatory cytokines in the brain and the potential use of gonadal steroids or their derivates in the immunomodulation of cerebral malaria.

Level of circulating steroid hormones in malaria and cutaneous leishmaniasis: a case control study

Epidemiological and clinical studies have shown a great difference in the severity and prevalence of infectious diseases in men and women and various studies have shown that the key immunological factors are affected by sex-associated hormones. Considering the role of sex hormones in various infections, the current study aimed to determine the level of sex hormones in patients with cutaneous leishmaniasis (CL) and malaria and compare it with those of healthy controls. The survey was designed as a case-control study. Peripheral blood was collected from thirty male malaria patients, sixty patients (equal number of both sexes) with cutaneous leishmaniasis and ninety healthy subjects. Disease confirmations were done through microscopic examination of either peripheral blood smears, in case of malaria, or Giemsa-stained lesion imprint slides for CL. The level of testosterone, progesterone and estrogen were measured in malaria and CL patients along with healthy subjects, using an ELISA commercial kit. Age of participants was 18-35 years (mean 25.39 ± 4.70) for CL patients and 14-41 years (mean 27.63 ± 9.09) for malaria patients. Differences between the age of patients and the healthy subjects were insignificant. The level of testosterone in malaria patients (1.44 ± 0.12 ng/mL) was lower than control group (1.46 ± 0.06, ng/mL) but the differences were not statistically significant (p > .05). The concentration of testosterone in CL patients (1.49 ± 0.03 ng/mL) was higher than those of control group (1.46 ± 0.06 ng/mL), and the difference was statistically significant (p  = 0.05). Although the concentration of estrogen and progesterone in CL patients were lower than controls, still the differences were not statistically significant (p > 0.05). Findings of the current study demonstrated a significant difference in the serum level of testosterone in CL patients in comparison with the healthy subjects whereas such difference was not seen in malaria patients.

Sex differences in tuberculosis

Tuberculosis is the most prevalent bacterial infectious disease in humans and the leading cause of death from a single infectious agent, ranking above HIV/AIDS. The causative agent, Mycobacterium tuberculosis, is carried by an estimated two billion people globally and claims more than 1.5 million lives each year. Tuberculosis rates are significantly higher in men than in women, reflected by a male-to-female ratio for worldwide case notifications of 1.7. This phenomenon is not new and has been reported in various countries and settings over the last century. However, the reasons for the observed gender bias are not clear, potentially highly complex and discussed controversially in the literature. Both gender- (referring to sociocultural roles and behavior) and sex-related factors (referring to biological aspects) likely contribute to higher tuberculosis rates in men and will be discussed.

Metabolomic changes in vertebrate host during malaria disease progression

Metabolomics refers to top-down systems biological analysis of metabolites in biological specimens. Phenotypic proximity of metabolites makes them interesting candidates for studying biomarkers of environmental stressors such as parasitic infections. Moreover, the host-parasite interaction directly impinges upon metabolic pathways since the parasite uses the host metabolite pool as a biosynthetic resource. Malarial infection, although not recognized as a classic metabolic disorder, often leads to severe metabolic changes such as hypoglycemia and lactic acidosis. Thus, metabolomic analysis of the infection has become an invaluable tool for promoting a better understanding of the host-parasite interaction and for the development of novel therapeutics. In this review, we summarize the current knowledge obtained from metabolomic studies of malarial infection in rodent models and human patients. Metabolomic analysis of experimental rodent malaria has provided significant insights into the mechanisms of disease progression including utilization of host resources by the parasite, sexual dimorphism in metabolic phenotypes, and cellular changes in host metabolism. Moreover, these studies also provide proof of concept for prediction of cerebral malaria. On the other hand, metabolite analysis of patient biofluids generates extensive data that could be of use in identifying biomarkers of infection severity and in monitoring disease progression. Through the use of metabolomic datasets one hopes to assess crucial infection-specific issues such as clinical severity, drug resistance, therapeutic targets, and biomarkers. Also discussed are nascent or newly emerging areas of metabolomics such as pre-erythrocytic stages of the infection and the host immune response. This review is organized in four broad sections-methodologies for metabolomic analysis, rodent infection models, studies of human clinical specimens, and potential of immunometabolomics. Data summarized in this review should serve as a springboard for novel hypothesis testing and lead to a better understanding of malarial infection and parasite biology.

Sex Steroids Mediate Bidirectional Interactions Between Hosts and Microbes

The outcome of microbial infections in mammals, including humans, is affected by the age, sex, and reproductive status of the host suggesting a role for sex steroid hormones. Testosterone, estradiol, and progesterone, signaling through their respective steroid receptors, affect the functioning of immune cells to cause differential susceptibility to parasitic, bacterial, and viral infections. Microbes, including fungi, bacteria, parasites, and viruses, can also use sex steroid hormones and manipulate sex steroid receptor signaling mechanisms to increase their own survival and replication rate. The multifaceted use of sex steroid hormones by both microbes and hosts during infection forms the basis of this review. In the arms race between microbes and hosts, both hosts and microbes have evolved to utilize sex steroid hormone signaling mechanisms for survival.

Impact of sex differences in brain response to infection with Plasmodium berghei

Malaria is considered to be one of the most prevalent diseases in the world. Severity of the disease between males and females is very important in clinical research areas. In this study, we investigated the impact of sex differences in brain response to infection with Plasmodium berghei. Male and female C57Bl/6 mice were infected with P. berghei-infected erythrocytes. The infection induced a significant change in weight loss in males (-7.2 % ± 0.5) than females (-4.9 % ± 0.6). The maximum parasitemia reached about 15 % at day 9 postinfection. Also, P. berghei infection caused histopathological changes in the brain of mice. These changes were in the form of inflammation, hemorrhage, and structural changes in Purkinje cells. In addition, P. berghei was able to induce a marked oxidative damage in mice brain. The infection induced a significant increase in male brain glutathione than females while the brain catalase level was significantly increased in infected females than infected males. Moreover, the change in brain neurotransmitters, dopamine, epinephrine, norepinephrine, and serotonin, was more in infected males than infected females. At the molecular level, P. berghei was able to induce upregulations of Adam23, Cabp1, Cacnb4, Glrb, and Vdac3-mRNA in the brain of mice. These genes were significantly upregulated in infected males than in infected females. In general, P. berghei could induce structural, biochemical, and molecular alterations in mice brain. Severity of these alterations was different according to sex of mice.

Parasite evolution in response to sex-based host heterogeneity in resistance and tolerance

Heterogenity between sexes in terms of both the level and the type of immune response to infection is documented in many species, but its role on parasite evolution is only beginning to be explored. We adopt an evolutionary epidemiology approach to study how the ability of a host to respond to infection through active immunity (resistance) or through minimizing deleterious effects of a given parasite load (tolerance) affects the evolution of parasite virulence. Consistently with earlier models, we find that increases in host resistance and tolerance both favour more virulent parasite strains. However, we show that qualitatively different results can be obtained if dimorphism between the sexes occurs through resistance or through tolerance depending on the contact pattern between the sexes. Finally, we find that variations in host sex ratio can amplify the consequences of heterogeneity for parasite evolution. These results are analysed in the light of several examples from the literature to illustrate the prevalence of sexually dimorphic immune responses and the potential for further study of the role of sexual dimorphism on parasite evolution. Such studies are likely to be highly relevant for improving treatment of chronic infections and control of infectious diseases, and understanding the role of sex in immune function.

Gonadal steroids negatively modulate oxidative stress in CBA/Ca female mice infected with P. berghei ANKA

We decreased the level of gonadal steroids in female and male mice by gonadectomy. We infected these mice with P. berghei ANKA and observed the subsequent impact on the oxidative stress response. Intact females developed lower levels of parasitaemia and lost weight faster than intact males. Gonadectomised female mice displayed increased levels of parasitaemia, increased body mass, and increased anaemia compared with their male counterparts. In addition, gonadectomised females exhibited lower specific catalase, superoxide dismutase, and glutathione peroxidase activities in their blood and spleen tissues compared with gonadectomised males. To further study the oxidative stress response in P. berghei ANKA-infected gonadectomised mice, nitric oxide levels were assessed in the blood and spleen, and MDA levels were assessed in the spleen. Intact, sham-operated, and gonadectomised female mice exhibited higher levels of nitric oxide in the blood and spleen compared with male mice. MDA levels were higher in all of the female groups. Finally, gonadectomy significantly increased the oxidative stress levels in females but not in males. These data suggest that differential oxidative stress is influenced by oestrogens that may contribute to sexual dimorphism in malaria.

Testosterone persistently dysregulates hepatic expression of Tlr6 and Tlr8 induced by Plasmodium chabaudi malaria

Testosterone (T) is known to induce persistent susceptibility to Plasmodium chabaudi malaria. Pathogens recognizing Toll-like receptors (TLRs), though potentially important against malaria, have not yet been examined for their T-sensitivity. Here, we investigate effects of T and P. chabaudi on mRNA expression and promoter DNA methylation of Tlr1-9 genes in the liver of female C57BL/6 mice. These are treated with T or vehicle for 3 weeks, and then treatment is discontinued for 12 weeks, before challenging with P. chabaudi for 8 days. Our data reveal that T induces a 9.1-fold downregulation of Tlr6 mRNA and 6.3-fold upregulation of Tlr8 mRNA. Blood-stage infections induce significant increases in mRNA expression of Tlr1, 2, 4, 6, 7, and 8 varying between 2.5-fold and 21-fold in control mice. In T-pretreated mice, these Tlr genes are also significantly responsive to infections. However, the malaria-induced upregulations of the relative mRNA expressions of Tlr6 and Tlr8 are 5.6-fold higher and 6.5-fold lower in T-pretreated mice than in control mice. Infections induce a massive DNA down-methylation of the Tlr6 gene promoter in control mice, which is still more pronounced in T-pretreated mice, while significant changes are not detectable for the DNA methylation status of the Tlr8 promoter. Our data support the view that hepatic expression of Tlr6, but not that of Tlr8 is epigenetically controlled, and that the dysregulations of Tlr6 and Tlr8 critically contribute to T-induced persistent susceptibility to P. chabaudi malaria, possibly by dys-balancing responses of TLR6-mediated pathogen recognition and TLR8-mediated generation of anti-malaria "protective" autoimmunity.

SeXX matters in immunity

The significant contributions of sex to an immune response, specifically in the context of the sex bias observed in susceptibility to infectious and autoimmune diseases and their pathogenesis, have until recently, largely been ignored and understudied. This review highlights recent findings related to sex-specific factors that provide new insights into how sex determines the transcriptome, the microbiome, and the consequent immune cell functional profile to define an immune response. Unquestionably, accumulating data confirm that sex matters and must be a consideration when decisions around therapeutic intervention strategies are developed.

A parent-of-origin effect determines the susceptibility of a non-informative F1 population to Trypanosoma cruzi infection in vivo

The development of Chagas disease is determined by a complex interaction between the genetic traits of both the protozoan parasite, T. cruzi, and the infected host. This process is regulated by multiple genes that control different aspects of the host-parasite interaction. While determination of the relevant genes in humans is extremely difficult, it is feasible to use inbred mouse strains to determine the genes and loci responsible for host resistance to infection. In this study, we investigated the susceptibility of several inbred mouse strains to infection with the highly virulent Y strain of T. cruzi and found a considerable difference in susceptibility between A/J and C57BL/6 mice. We explored the differences between these two mouse strains and found that the A/J strain presented higher mortality, exacerbated and uncontrolled parasitemia and distinct histopathology in the target organs, which were associated with a higher parasite burden and more extensive tissue lesions. We then employed a genetic approach to assess the pattern of inheritance of the resistance phenotype in an F1 population and detected a strong parent-of-origin effect determining the susceptibility of the F1 male mice. This effect is unlikely to result from imprinted genes because the inheritance of this susceptibility was affected by the direction of the parental crossing. Collectively, our genetic approach of using the F1 population suggests that genes contained in the murine chromosome X contribute to the natural resistance against T. cruzi infection. Future linkage studies may reveal the locus and genes participating on the host resistance process reported herein.

Testosterone-induced persistent susceptibility to Plasmodium chabaudi malaria: long-term changes of lincRNA and mRNA expression in the spleen

Testosterone (T) is known to induce persistent susceptibility to blood-stage malaria of Plasmodium chabaudi in otherwise resistant female C57BL/6 mice, which is associated with permanent changes in mRNA expression of the liver. Here, we investigate the spleen as the major effector against blood-stage malaria for any possible T-induced long-term effects on lincRNA and mRNA expression. Female C57BL/6 mice were treated with T for 3 weeks, then T was withdrawn for 12 weeks before challenging with P. chabaudi. LincRNA and mRNA expression was examined after 12 weeks of T-withdrawal and after subsequent infections using Agilent whole mouse genome oligo microarrays. Our data show for the first time long-term effects of T on lincRNA expression evidenced directly as persistent changes after T-withdrawal for 12 weeks and indirectly as altered responsiveness of expression to P. chabaudi infections. There are 3 lincRNA-species upregulated and 10 lincRNAs downregulated by more than 2-fold (p<0.01). In addition, 11 and 10 mRNAs are persistently up- and downregulated by T, respectively. These changes remain not sustained during infections at peak parasitemia, when 15 other lincRNAs and 9 other mRNAs exhibit an altered expression. The only exception is the Tnk1-mRNA encoding the non-receptor tyrosine kinase 1 that is persistently downregulated by 0.34-fold after T-withdrawal and that becomes upregulated by 5.9-fold upon infection at peak parasitemia, suggesting an involvement of tyrosine phosphorylation by Tnk1 in mediating long-term effects of T in the spleen. The T-induced changes in splenic mRNA expression are totally different to those previously observed in the liver. Collectively, our data support the view that T induces long-term organ-specific changes in both lincRNA and mRNA expression, that presumably contribute to organ-specific dysfunctions upon infection with blood-stage malaria of P. chabaudi.

Organ-specific testosterone-insensitive response of miRNA expression of C57BL/6 mice to Plasmodium chabaudi malaria

Increasing evidence critically implicates miRNAs in the pathogenesis of diseases, but little is known in context with infectious diseases. This study investigates as to whether the testosterone-induced persistent susceptibility to blood-stage malaria of Plasmodium chabaudi coincides with changes in miRNA expression of the anti-malaria effectors sites spleen and liver. Female C57BL/6 mice were treated with vehicle or testosterone (T) for 3 weeks. Then, T treatment was discontinued for 12 weeks before challenge with 10(6) P. chabaudi-parasitized erythrocytes. The miRNA expression was examined after 12 weeks of T withdrawal and during infections at peak parasitemia on day 8 p.i. using miRXplore™ microarray technology. P. chabaudi infections induce an organ-specific response of miRNA expression. We can identify 25 miRNA species to be downregulated by more than 2-fold in the spleen and 169 miRNA species in the liver. Among these 194 miRNA species, there are 12 common miRNA species that are downregulated by 0.48-0.14-fold in both spleen and liver, which are miR-194, miR-192, miR-193A-3P, miR-145, miR-16, miR-99A, miR-99B, miR-15A, miR-152, let-7G, let-7B, and miR-455-3P. Only in the liver, there is an upregulation of the miR-142-5p by 2.5-fold and miR-342-3p by 5.1-fold. After 12 weeks of T withdrawal, the spleen exhibits only the miR-200A that is upregulated by 2.7-fold. In the liver, miR-376B, miR-493*, and miR-188-3P are upregulated by 2.4-fold, 2.2-fold, and 2.1-fold, respectively, and miR-347, miR-200A, and miR-200B are downregulated by approximately 0.4-fold. Upon infection, however, these changes are not sustained, i.e., the miRNA expressions of both spleen and liver of T-pretreated mice exhibit the same response to P. chabaudi malaria as that of vehicle-treated control mice. Our data suggest (1) that the P. chabaudi-induced downregulation of miRNA expression in spleen and liver is required to allow the upregulation of their numerous target genes in response to infection, and (2) that the T-induced persistent susceptibility to P. chabaudi does not affect the responsiveness of miRNA expression in spleen and liver to blood-stage malaria.

Age-dependent sex bias in clinical malarial disease in hypoendemic regions

BACKGROUND AND OBJECTIVES

Experimental models show a male bias in murine malaria; however, extant literature on biases in human clinical malaria is inconclusive. Studies in hyperendemic areas document an absence of sexual dimorphism in clinical malaria. Data on sex bias in clinical malaria in hypoendemic areas is ambiguous--some reports note a male bias but do not investigate the role of differential mosquito exposure in that bias. Moreover, these studies do not examine whether the bias is age related. This study investigates whether clinical malaria in hypoendemic regions exhibits a sex bias and whether this bias is age-dependent. We also consider the role of vector exposure in this bias.

METHODS

Retrospective passive clinical malaria datasets (2002-2007) and active surveillance datasets (2000-2009) were captured for the hypoendemic Mumbai region in Western India. To validate findings, passive retrospective data was captured from a primary malaria clinic (2006-2007) in hypoendemic Rourkela (Eastern India). Data was normalized by determining percent slide-positivity rates (SPRs) for males and females, and parasite-positivity distributions were established across age groups. The Mann-Whitney test, Wilcoxon Signed Rank test, and Chi-square analysis were used to determine statistical significances.

RESULTS

In both the Mumbai and Rourkela regions, clinical malaria exhibited an adult male bias (p<0.01). A sex bias was not observed in children aged ≤10. Post-puberty, male SPRs were significantly greater than females SPRs (p<0.01). This adult male bias was observed for both vivax and falciparum clinical disease. Analysis of active surveillance data did not reveal an age or sex bias in the frequency of parasite positivity.

CONCLUSION

This study demonstrates an age-dependent sex bias in clinical malaria in hypoendemic regions and enhanced incidence of clinical malaria in males following puberty. Possible roles of sex hormones, vector exposure, co-infections, and other factors in this enhanced susceptibility are discussed.

Insufficiently defined genetic background confounds phenotypes in transgenic studies as exemplified by malaria infection in Tlr9 knockout mice

The use of genetically modified mice, i.e. transgenic as well as gene knockout (KO) and knock-in mice, has become an established tool to study gene function in many animal models for human diseases . However, a gene functions in a particular genomic context. This implies the importance of a well-defined homogenous genetic background for the analysis and interpretation of phenotypes associated with genetic mutations. By studying a Plasmodium chabaudi chabaudi AS (PcAS) malaria infection in mice bearing a TLR9 null mutation, we found an increased susceptibility to infection, i.e. higher parasitemia levels and increased mortality. However, this was not triggered by the deficient TLR9 gene itself. Instead, this disease phenotype was dependent on the heterogeneous genetic background of the mice, which appeared insufficiently defined as determined by single nucleotide polymorphism (SNP) analysis. Hence, it is of critical importance to study gene KO phenotypes on a homogenous genetic background identical to that of their wild type (WT) control counterparts. In particular, to avoid problems related to an insufficiently defined genetic background, we advocate that for each study involving genetically modified mice, at least a detailed description of the origin and genetic background of both the WT control and the altered strain of mice is essential.

Genetic control of susceptibility to infection with Plasmodium chabaudi chabaudi AS in inbred mouse strains

To identify genetic effects modulating blood stage replication of the malarial parasite, we phenotyped a group of 25 inbred mouse strains for susceptibility to Plasmodium chabaudi chabaudi AS infection (peak parasitemia, survival). A broad spectrum of responses was observed, with strains such as C57BL/6J being the most resistant (low parasitemia, 100% survival), and strains such as NZW/LacJ and C3HeB/FeJ being extremely susceptible (very high parasitemia and uniform lethality). A number of strains showed intermediate phenotypes and gender specific effects, suggestive of rich genetic diversity in response to malaria in inbred strains. An F2 progeny were generated from SM/J (susceptible) and C57BL/6J (resistant) parental strains, and was phenotyped for susceptibility to P. chabaudi chabaudi AS. A whole genome scan in these animals identified the Char1 locus (LOD=7.40) on chromosome 9 as a key regulator of parasite density and pointed to a conserved 0.4Mb haplotype at Char1 that segregates with susceptibility/resistance to infection. In addition, a second locus was detected in [SM/J x C57BL/6J] F2 mice on the X chromosome (LOD=4.26), which was given the temporary designation Char11. These studies identify a conserved role of Char1 in regulating response to malaria in inbred mouse strains, and provide a prioritized 0.4Mb interval for the search of positional candidates.

Testosterone response of hepatic gene expression in female mice having acquired testosterone-unresponsive immunity to Plasmodium chabaudi malaria

Blood-stage malaria of Plasmodium chabaudi is characterized by its responsiveness to testosterone (T): T suppresses development of protective immunity, whereas once acquired immunity is T-unresponsive. Here, we have analyzed the liver, a T target and lymphoid organ with anti-malaria activity, for its T-responsiveness of gene expression in immune mice. Using Affymetrix microarray technology, in combination with quantitative RT-PCR, we have identified (i) T-unresponsive expression of newly acquired mRNAs encoding diverse sequences of IgG- and IgM-antibodies, (ii) 24 genes whose expression has become T-unresponsive including those encoding the T(H)2 response promoting EHMT2 and the erythrocyte membrane protein band 7.2 STOM, (iii) T-unresponsive expression of mRNAs for the cytokines IL-1β, IL-6, TNFα, and IFNγ, as well as iNOS, which are even not inducible by infection, and (iv) 35 genes retaining their T-responsiveness, which include those encoding the infection-inducible acute phase proteins SAA1, SAA2, and ORM2 as well as those of liver metabolism which encode the T-downregulated female-prevalent enzymes CYP2B9, CYP2B13, CYP3A41, CYP7A1, and SULT2A2 and the T-upregulated male-prevalent enzymes CYP2D9, CYP7B1, UGT2B1, HSD3B2, HSD3B5, respectively. The mRNA of the latter T-metabolizing enzyme is even 5-fold increased by T, suggesting a decrease in the effective T concentrations in the liver of immune mice. Collectively, our data suggest that the liver, which has acquired a selective T-unresponsiveness of gene expression, contributes to the acquired T-unresponsive, antibody-mediated protective immunity to blood-stage malaria of P. chabaudi.

Gender specific differences in the immune response to infection

There are many instances where males and females differ in the susceptibility to infections. The reason for these differences in susceptibility is multifactorial. The primary cause is thought to be due to differences induced by sex hormones and their effects on gene expression as well as the immune system, but may also be due to innate physiological differences between males and females. This review summarizes gender specific differences seen in infections caused by bacteria, fungi, parasites and viruses. Ultimately, gender specific differences appear to be dependent on the microbe causing the infection, as not every infection with a specific microbial type results in increased susceptibility of one gender over the other. This suggests that there is an interaction between gender specific immune differences and the specific immune response to individual microbes.

Alterations in urine, serum and brain metabolomic profiles exhibit sexual dimorphism during malaria disease progression

Background

Metabolic changes in the host in response to Plasmodium infection play a crucial role in the pathogenesis of malaria. Alterations in metabolism of male and female mice infected with Plasmodium berghei ANKA are reported here.

Methods

¹H NMR spectra of urine, sera and brain extracts of these mice were analysed over disease progression using Principle Component Analysis and Orthogonal Partial Least Square Discriminant Analysis.

Results

Analyses of overall changes in urinary profiles during disease progression demonstrate that females show a significant early post-infection shift in metabolism as compared to males. In contrast, serum profiles of female mice remain unaltered in the early infection stages; whereas that of the male mice changed. Brain metabolite profiles do not show global changes in the early stages of infection in either sex. By the late stages urine, serum and brain profiles of both sexes are severely affected. Analyses of individual metabolites show significant increase in lactate, alanine and lysine, kynurenic acid and quinolinic acid in sera of both males and females at this stage. Early changes in female urine are marked by an increase of ureidopropionate, lowering of carnitine and transient enhancement of asparagine and dimethylglycine. Several metabolites when analysed individually in sera and brain reveal significant changes in their levels in the early phase of infection mainly in female mice. Asparagine and dimethylglycine levels decrease and quinolinic acid increases early in sera of infected females. In brain extracts of females, an early rise in levels is also observed for lactate, alanine and glycerol, kynurenic acid, ureidopropionate and 2-hydroxy-2-methylbutyrate.

Conclusions

These results suggest that P. berghei infection leads to impairment of glycolysis, lipid metabolism, metabolism of tryptophan and degradation of uracil. Characterization of early changes along these pathways may be crucial for prognosis and better disease management. Additionally, the distinct sexual dimorphism exhibited in these responses has a bearing on the understanding of the pathophysiology of malaria.

Loss of ability to self-heal malaria upon taurine transporter deletion

Deletion of the taurine transporter gene (taut) results in lowered levels of taurine, the most abundant amino acid in mammals. Here, we show that taut-/- mice have lost their ability to self-heal blood-stage infections with Plasmodium chabaudi malaria. All taut-/- mice succumb to infections during crisis, while about 90% of the control taut(+/+) mice survive. The latter retain unchanged taurine levels even at peak parasitemia. Deletion of taut, however, results in the lowering of circulating taurine levels from 540 to 264 micromol/liter, and infections cause additional lowering to 192 micromol/liter. Peak parasitemia levels in taut-/- mice are approximately 60% higher than those in taut(+/+) mice, an elevation that is associated with increased systemic tumor necrosis factor alpha (TNF-alpha) and interleukin-1beta (IL-1beta) levels, as well as with liver injuries. The latter manifest as increased systemic ammonia levels, a perturbed capacity to entrap injected particles, and increased expression of genes encoding TNF-alpha, IL-1beta, IL-6, inducible nitric oxide synthase (iNOS), NF-kappaB, and vitamin D receptor (VDR). Autopsy reveals multiorgan failure as the cause of death for malaria-infected taut-/- mice. Our data indicate that taut-controlled taurine homeostasis is essential for resistance to P. chabaudi malaria. Taurine deficiency due to taut deletion, however, impairs the eryptosis of P. chabaudi-parasitized erythrocytes and expedites increases in systemic TNF-alpha, IL-1beta, and ammonia levels, presumably contributing to multiorgan failure in P. chabaudi-infected taut-/- mice.

Gonadectomy inhibits development of experimental amoebic liver abscess in hamsters through downregulation of the inflammatory immune response

Incidence of amoebic liver abscess (ALA) in human males is considerably higher than in females, suggesting a role for sex hormones in this parasite infection. We describe here the effect of hamster gonadectomization on the development of ALA. After monitoring the decrease of oestradiol in females and testosterone in males to undetectable levels by ELISA and Radio Immuno Assay (RIA) in serum, hamsters were intraportally infected with Entamoeba histolytica trophozoites and killed 7 days later. ALA was absent in 50% of male and 15% of female gonadectomized (Gdx) hamsters, in comparison with 100% infection in non-Gdx controls. This protection against ALA in Gdx hamsters was concomitant to a comparatively scarce inflammatory infiltrate and necrosis surrounding clusters of trophozoites in the liver tissue, as well as to a lack of response of spleen cells to Con A, evaluated in proliferation assays. As tissue damage in ALA has been associated with a local inflammatory Th1 response, we determined the profile of response in hamsters by immunohistochemistry on liver sections. In contrast to strong Th1 responses in non-Gdx animals, Gdx females and males exhibited Th2 and Th3 profiles of cytokines, respectively, suggesting that protection against ALA following gonadectomization, could be related to downregulation of liver Th1 response during amoebic infection.

Mapping of Char10, a novel malaria susceptibility locus on mouse chromosome 9

Resistance to blood-stage malaria in AcB55 and AcB61 is caused by a loss of function mutation in pyruvate kinase (Pklr(I90N)). Likewise, pyruvate kinase (PK) deficiency in humans is protective against Plasmodium replication in vitro. We identified a third AcB strain, AcB62 that also carries the Pklr(I90N) mutation. However, AcB62 mice were susceptible to P.chabaudi infection and showed high levels of parasite replication (54-62% peak parasitemia). AcB62 mice showed the hallmarks of PK deficiency-associated anemia similar to AcB55/61 with reticulocytosis, splenic red pulp expansion, tissue iron overload, and increased expression of iron metabolism proteins. This suggests that malaria susceptibility in AcB62 is not because of absence of PK deficiency-associated pathophysiology. To map novel genetic factors affecting malaria susceptibility in AcB62, we generated an informative F2 population using AcB62 (Pklr(I90N)) and CBA-Pk(slc) (Pklr(G338D)) as progenitors and identified a novel locus on chromosome 9 (Char10; LOD=7.24) that controls peak parasitemia. A weaker linkage to the Pklr region of chromosome 3 (LOD=3.7) was also detected, a finding that may reflect the segregation of the two defective Pklr alleles. AcB62 alleles at both loci are associated with higher peak parasitemia. These results identify Char10 as a novel locus modulating severity of malaria in the context of PK deficiency.

Estrogen and progesterone affect responses to malaria infection in female C57BL/6 mice

BACKGROUND

Previous data from our laboratory suggest that gonadally intact C57BL/6 male mice are more likely than their female counterparts to die from Plasmodium chabaudi infection, to recover more slowly from weight loss and hematocrit loss, and to have reduced interferon-gamma (IFN-gamma) and interleukin-10 (IL-10) responses. Removal of the ovaries, and hence, the primary production of sex steroids in females, reverses these differences.

OBJECTIVE

We hypothesized that sex differences in response to P chabaudi may be mediated by differential synthesis of IFN-gamma and IL-10 that is influenced by estrogen, progesterone, or both.

METHODS

C57BL/6 female mice (n = 200; n = 10/time point/treatment/experiment) were ovariectomized and implanted with a 21-day controlled-release pellet containing either 0.1 mg of 17beta-estradiol (E(2)), 10 mg of progesterone (P(4)), 0.1 mg of E(2) plus 10 mg of P(4), or cholesterol (placebo). Females were inoculated with 10(6)P chabaudi-infected erythrocytes. Body mass, body temperature, hematocrit, parasitemia, cytokine production, and antibody responses were monitored 0, 3, 5, 7, 10, 14, and 21 days postinoculation.

RESULTS

Administration of E(2), either alone or in combination with P(4), mitigated infection-induced weight loss, hematocrit loss, and hypothermia, compared with females receiving placebo pellets (P < 0.05 in each case). Hormone treatment did not affect levels of parasitemia. Females administered E(2) alone or in combination with P(4) produced 4 to 7 times higher IFN-gamma and IL-10 during peak parasitemia than did females implanted with pellets containing either P(4) alone or placebo (P < 0.05 in each case). Exposure to E(2), either alone or in combination with P(4), increased anti-P chabaudi immunoglobulin G (IgG1) responses and the ratio of IgG1 to IgG2c (P < 0.05 in each case).

CONCLUSION

This animal study suggests that physiological levels of estrogen, rather than progesterone, enhance immunity and, possibly, protect females from disease symptoms during malaria infection.

Influence sexual dimorphism on the persistence of blood parasites in infected Calomys callosus

Gender has long been known to be a contributory factor in the incidence and progression of disorders associated with immune system disregulation. The aims of this experiment were to verify the influences of sexual dimorphism on the persistence of blood parasites out of the acute phase of infection. Male and female Calomys callosus were separated and infected with two strains of Trypanosoma cruzi, and let age until 120 days. Xenogiagnostic, culture of organs and blood, histopathology and lytic antibody percentages were evaluated on late chronic phase. Xenodiagnosis, hemoculture and lytic antibody percentages were positive from 45 until 120 days. For both strains in adrenal and heart, amastigote burdens were present until 45 days, scarcely found on 60 days and absent on 120 days. Steroid hormones, although having a protective role, does not enable animals to get completely rid of the infection. Even without showing apparent signs of pathological unbalance, parasites persists, hidden throughout the host's body.

Involvement of gonadal steroids and gamma interferon in sex differences in response to blood-stage malaria infection

To examine the hormonal and immunological mechanisms that mediate sex differences in susceptibility to malaria infection, intact and gonadectomized (gdx) C57BL/6 mice were inoculated with Plasmodium chabaudi AS-infected erythrocytes, and the responses to infection were monitored. In addition to reduced mortality, intact females recovered from infection-induced weigh loss and anemia faster than intact males. Expression microarrays and real-time reverse transcription-PCR revealed that gonadally intact females exhibited higher expression of interleukin-10 (IL-10), IL-15Ralpha, IL-12Rbeta, Gadd45gamma, gamma interferon (IFN-gamma), CCL3, CXCL10, CCR5, and several IFN-inducible genes in white blood cells and produced more IFN-gamma than did intact males and gdx females, with these differences being most pronounced during peak parasitemia. Intact females also had higher anti-P. chabaudi immunoglobulin G (IgG) and IgG1 responses than either intact males or gdx females. To further examine the effector mechanisms mediating sex differences in response to P. chabaudi infection, responses to infection were compared among male and female wild-type (WT), T-cell-deficient (TCRbetadelta-/-), B-cell-deficient (microMT), combined T- and B-cell-deficient (RAG1), and IFN-gamma knockout (IFN-gamma-/-) mice. Males were 3.5 times more likely to die from malaria infection than females, with these differences being most pronounced among TCRbetadelta-/-, microMT, and RAG1 mice. Male mice also exhibited more severe weight loss, anemia, and hypothermia, and higher peak parasitemia than females during infection, with WT, RAG1, TCRbetadelta-/-, and microMT mice exhibiting the most pronounced sexual dimorphism. The absence of IFN-gamma reduced the sex difference in mortality and was more detrimental to females than males. These data suggest that differential transcription and translation of IFN-gamma, that is influenced by estrogens, may mediate sex differences in response to malaria.

Estradiol, but not dehydroepiandrosterone, decreases parasitemia and increases the incidence of cerebral malaria and the mortality in plasmodium berghei ANKA-infected CBA mice

OBJECTIVE

The effect of castration and subsequent replacement of dehydroepiandrosterone (DHEA) or estradiol on parasitemia, mortality and incidence of cerebral malaria (CM) was evaluated in CBA mice infected with Plasmodium berghei ANKA.

METHODS

Female mice were castrated, and groups of 12-15 animals received daily injections of DHEA, estradiol or saline. Four days after the start of treatment, mice were inoculated with 1 x 10(6)P. berghei ANKA-parasitized erythrocytes. DHEA treatment was continued during the 5 days after infection, and estradiol was administered during the follow-up. Parasitemia was evaluated daily in Giemsa-stained blood smears. Signs of CM were determined by the manifestation of coma, limb paralysis and/or convulsions. Plasma TNF-alpha levels were evaluated by sandwich ELISA. Nitric oxide synthase (NOS) activity in the brain of moribund mice was measured by the method of Bredt and Snyder.

RESULTS

In non-castrated infected mice, the incidence of CM was 50%, and plasma TNF-alpha increased and brain NOS activity decreased compared to non-infected controls. Castration had no major effect on the parameters analyzed (parasitemia, mortality, CM incidence, TNF-alpha levels or NOS activity). Estradiol replacement caused a decrease in parasitemia but resulted in higher CM incidence and faster mortality, with an increase in NOS activity.

CONCLUSIONS

Estradiol modulated the immune response of P. berghei ANKA-infected CBA mice, decreasing parasitemia and increasing NOS activity, and impacted negatively on survival and CM incidence, showing that neuroimmunoendocrine interactions are important in the physiopathogenesis of malaria infections.

Malaria-suppressible expression of the anti-apoptotic triple GTPase mGIMAP8

The IMAP/IAN family of AIG1-like GTPases is conserved among vertebrates and angiosperm plants and has been postulated to regulate apoptosis, particularly in context with diseases such as cancer, diabetes, and infections. The human genes were recently renamed as gimap for GTPase of the immunity associated protein (GIMAP) family. Here we extend this new nomenclature to the murine gimap gene family. All gimap genes of the mouse are clustered on chromosome 6B with eight functional members and one pseudogene. The mGIMAP proteins contain one GTP-binding site and display molecular masses between 33 and 38 kDa except for the very unusual 77 kDa mGIMAP8 protein, which is the first characterized protein containing three GTP-binding domains. Northern blot analysis revealed expression of mgimap8 predominantly in the thymus. The low expression level observed in the spleen was further suppressed by Plasmodium chabaudi malaria. Confocal laser scanning microscopy demonstrated localization of mGIMAP8 at ER, Golgi, and mitochondria. Overexpression of mGIMAP8 could significantly impair anisomycin-induced activation of caspase 3. Our data support the view that mGIMAP8 exerts an anti-apoptotic effect in the immune system and is involved in responses to infections.

Deletion of LTbetaR augments male susceptibility to Plasmodium chabaudi

SUMMARY Disruption of the lymphotoxin beta receptor (LTbetaR) gene has been shown to result in enhanced resistance of female mice to blood-stage Plasmodium chabaudi malaria. Here, we investigate the effect of LTbetaR deletion on host defence of males. In contrast to females, male LTbetaR(-/-) mice do not exhibit any increase in resistance. Conversely, they are even more susceptible than wild-type C57BL/6 mice, which becomes evident after lowering circulating levels of testosterone by castration, which makes C57BL/6 males resistant, whereas LTbetaR(-/-) remain susceptible. Gene-expression analysis using cDNA arrays revealed no differences in immunological responses in spleen of malaria-resistant female and malaria-susceptible castrated male LTbetaR(-/-) mice. In the liver, however, expression levels of plasminogen activator inhibitor PAI1, chemokine CXCL10, dual specificity phosphatase DUSP1, and hydroxysteroid-specific sulfotransferases Sult2a1/2 were decreased 6- to 85-fold in susceptible castrated male LTbetaR(-/-) mice in comparison to resistant female LTbetaR(-/-) mice at maximal parasitaemia, as evidenced by Northern blot analyses. The present data support our previous view that the liver is involved in the combat against malarial blood stages and that down-regulation of the genes DUSP1 and Sult2a1/2 signals dysregulation of protective liver responses, thus possibly contributing to male susceptibility of LTbetaR(-/-) mice.

Testosterone responsiveness of spleen and liver in female lymphotoxin β receptor-deficient mice resistant to blood-stage malaria

Disrupted signaling through lymphotoxin beta receptor (LTbetaR) results in severe defects of the spleen and even loss of all other secondary lymphoid tissues, making mice susceptible to diverse infectious agents. Surprisingly, however, we find that female LTbetaR-deficient mice are even more resistant to blood stages of Plasmodium chabaudi malaria than wild-type C57BL/6 mice. Higher resistance of LTbetaR-deficient mice correlates with an earlier onset of reticulocytosis, and the period of anemia is shorter. After surviving fulminant parasitemias of about 35%, mice develop long-lasting protective immunity against homologous rechallenge, with both spleen and liver acting as anti-malaria effectors. Testosterone suppresses resistance, i.e. all mice succumb to infections during or shortly after peak parasitemia. At peak parasitemia, testosterone does not essentially affect cellularity and apoptosis in the spleen, but aggravates liver pathology in terms of increased cell swelling, numbers of apoptotic and binucleated cells and reduced serum alkaline phosphatase levels, and conversely, reduces inflammatory lymphocytic infiltrates in the liver. In the spleen, hybridization of cDNA arrays identified only a few testosterone-induced changes in gene expression, in particular upregulation of INFgamma and IFN-regulated genes. By contrast, a much larger number of testosterone-affectable genes was observed in the liver, including genes involved in regulation of the extracellular matrix, in chemokine and cytokine signaling, and in cell cycle control. Collectively, our data suggest that testosterone dysregulates the inflammatory response in spleen and liver during their differentiation to anti-malaria effectors in malaria-resistant female LTbetaR-deficient mice, thus contributing to the testosterone-induced lethal outcome of malaria.

Testosterone suppresses protective responses of the liver to blood-stage malaria

Testosterone induces a lethal outcome in otherwise self-healing blood-stage malaria caused by Plasmodium chabaudi. Here, we examine possible testosterone effects on the antimalaria effectors spleen and liver in female C57BL/6 mice. Self-healing malaria activates gating mechanisms in the spleen and liver that lead to a dramatic reduction in trapping activity, as measured by quantifying the uptake of 3-mum-diameter fluorescent polystyrol particles. However, testosterone delays malaria-induced closing of the liver, but not the spleen. Coincidently, testosterone causes an approximately 3- to 28-fold depression of the mRNA levels of nine malaria-responsive genes, out of 299 genes tested, only in the liver and not in the spleen, as shown by cDNA arrays and Northern blotting. Among these are the genes encoding plasminogen activator inhibitor (PAI1) and hydroxysteroid sulfotransferase (STA2). STA2, which detoxifies bile acids, is suppressed 10-fold by malaria and an additional 28-fold by testosterone, suggesting a severe perturbation of bile acid metabolism. PAI1 is protective against malaria, since disruption of the PAI1 gene results in partial loss of the ability to control the course of P. chabaudi infections. Collectively, our data indicate that the liver rather than the spleen is a major target organ for testosterone-mediated suppression of resistance against blood-stage malaria.

Hormonal and immunological mechanisms mediating sex differences in parasite infection

The prevalence and intensity of infections caused by protozoa, nematodes, trematodes, cestodes, and arthropods is higher in males than females. The primary thesis of this review is that immunological differences exist between the sexes that may underlie increased parasitism in males compared to females. Several field and laboratory studies link sex differences in immune function with circulating steroid hormones; thus, the roles of sex steroids, including testosterone, oestradiol, and progesterone, as well as glucocorticoids will be discussed. Not only can host hormones affect responses to infection, but parasites can both produce and alter hormone concentrations in their hosts. The extent to which changes in endocrine-immune interactions following infection are mediated by the host or the parasite will be considered. Although males are more susceptible than females to many parasites, there are parasites for which males are more resistant than females and endocrine-immune interactions may underlie this sex reversal. Finally, although immunological differences exist between the sexes, genetic and behavioural differences may explain some variability in response to infection and will be explored as alternative hypotheses for how differences between the sexes contribute to dimorphic responses to parasites.

Developmental regulation of intracellular and surface androgen receptors in T cells

Increasing information indicates that testosterone actions on cells are mediated not only through the classical intracellular androgen receptor (iAR), but also through membrane androgen receptors (mAR) on cell surfaces. Here, we investigate the expression pattern of mAR and iAR in thymic T cells, which is compared with that of splenic T cells. Thymic T cells are testosterone-sensitive in vivo, i.e. treatment of female C57BL/10 mice with testosterone for 3 weeks decreased the total number of thymic T cells by approximately 90%. The percentage of CD4(-) CD8(-) T cells increased, whereas that of the subsequent CD4(+) CD8(+) T cells was diminished. Flow cytometry and confocal laser scanning microscopy (CLSM) with different anti-iAR antibodies localized iAR predominantly in the cytoplasm, but not on the surface of thymic T cells. The iAR are functionally active since the iAR are induced by testosterone to translocate from cytoplasm to nucleus, and they bind the testosterone analogue 3H-R1881 with high affinity (K(d) approximately 2.2 nM) and saturable capacity (approximately 10,000 binding sites per cell) as determined by Scatchard analysis. By contrast, the impeded ligand testosterone-BSA-FITC (T-BSA-FITC) did not bind to the surface of thymic T cells. In accordance, testosterone was unable to induce any rapid rise in the intracellular free Ca(2+) concentration of Fura-2 loaded thymocytes. This indicates that thymic T cells do not express any significant amounts of mAR. Conversely, splenic T cells express functionally active mAR, whereas their expressed iAR are not functional in the genomic pathway. Our results support the view of a delicately balanced developmental regulation of iAR and mAR in T cells.

Nongenomic testosterone calcium signaling. Genotropic actions in androgen receptor-free macrophages

Steroid hormones exert genotropic actions through members of the nuclear receptor family. Here, we have demonstrated genotropic actions of testosterone that are independent of intracellular androgen receptors (iAR). Through plasma membrane androgen receptors (mAR), testosterone induces a rapid rise in the intracellular free Ca(2+) concentration of iAR-free murine RAW 264.7 macrophages. This nongenomic testosterone signaling, which is independent of both iAR and estrogen receptors, does not in itself activate either the mitogen-activated protein kinase (MAPK) families ERK1/2, p38, and JNK/SAPK, the stably and transiently transfected c-fos promoter, or NO production. In the context of lipopolysaccharide (LPS) signaling, however, testosterone attenuates LPS activation of the c-fos promoter and NO production, which is abolished by the intracellular Ca(2+) chelator BAPTA. Testosterone also attenuates the LPS activation of p38 but not that of ERK1/2 and JNK/SAPK, and this attenuation is abrogated by BAPTA. Moreover, the p38 inhibitor, SB 203580, largely reduces LPS activation of the c-fos promoter and NO production, and the remaining levels are no longer regulated by testosterone. This study is the first to provide information on genotropic actions of mAR-mediated nongenomic testosterone Ca(2+) signaling by cross-talk with the LPS signaling pathway through p38 MAPK with impact on cell function.

Testosterone signaling in T cells and macrophages

This review summarizes data about non-genomic actions of testosterone on murine malaria, T cells and macrophages produced by our group during the last 15 years. In C57BL/10 mice, testosterone induces a lethal outcome of blood stage infections with Plasmodium chabaudi which normally takes a self-healing course controlled by genes of the H-2 complex and the non-H-2 background. This suppressive effect of testosterone is mediated neither via the classic intracellular androgen receptor (AR) response nor, after conversion of testosterone to estradiol, via the estrogen receptor. Testosterone acts non-genomically, i.e. through surface receptors, on murine T cells and macrophages, which becomes evident as a rapid rise in the intracellular free Ca(2+) concentration ([Ca(2+)](i)). In T cells, this rise reflects predominantly influx of extracellular Ca(2+), while it is predominantly due to release of Ca(2+) from intracellular Ca(2+)-stores in macrophages. The testosterone-induced rise in [Ca(2+)](i) of both macrophages and T cells is not inhibited by the AR-blocker cyproterone, and it is also inducible by the plasma membrane impermeable ligand testosterone-BSA. The surface receptors initiate a transcription-independent signaling pathway of testosterone. Currently, we are trying to isolate testosterone surface receptors and to investigate a possible cross-talk of non-genomic testosterone signaling with other genotropic signaling pathways.

Possible modulation by male sex hormone of Th1/Th2 function in protection against Plasmodium chabaudi chabaudi AS infection in mice

Zhang, Z.-H., Chen, L., Saito, S., Kanagawa, O., and Sendo, F. 2000. Possible modulation by male sex hormone of Th1/Th2 function in protection against Plasmodium chabaudi chabaudi AS infection in mice. Experimental Parasitology 96, 121-129. We examined the mortality, survival time, and parasitemia in interferon gamma receptor (IFN-gamma R)-deficient (IFN-gamma R(-/-)) and IL-4-deficient (IL-4(-/-)) mice infected with Plasmodium chabaudi AS and compared them with the wild type counterparts (IFN-gamma R(+/+) and IL-4(+/+), respectively). (1) Mortality was higher and survival time was shorter in males of both IFN-gamma R(-/-) and IL-4(-/-) mice infected with P. chabaudi AS, compared with their wild type counterparts, whereas such a difference was not observed in female mice. (2) These differences between males and females were not observed when male mice were castrated; however, female castration had no effect on the data. (3) The rate of parasitemia in both male and female IFN-gamma R(-/-) and IL-4(-/-) mice was higher at some points during the observation than in the wild type counterparts. (4) These results on susceptibility vs resistance to P. chabaudi AS infection can be explained partially by the levels of expression of Th1/Th2 cytokine and chemokine mRNAs in the spleen cells of the infected mice. These results suggest that male sex hormones modulate the function of Th1/Th2 cells and that these T cells counteract the activity of these hormones in protection against P. chabaudi AS infection in mice.

Spleen-specific expression of the malaria-inducible intronless mouse gene imap38

We characterize the mouse gene imap38 and its inducibility by Plasmodium chabaudi malaria among different lymphoid tissues and mouse strains of different H-2 complex and non-H-2 background. Imap38 is a single copy gene assigned to chromosome 6B. It consists of only one exon of 1900 base pairs encoding a highly basic 25.8-kDa protein. Confocal laser scanning microscopy localizes differently tagged IMAP38 proteins in nuclei of transfected cells. Reporter gene assays reveal that the 1730-base pair 5'-flanking region, containing an RSINE1 repeat immediately adjacent to initiation site +1, exhibits promoter activity in nonmurine cells, while it is largely repressed in diverse mouse cell lines, which corresponds to the situation in mouse tissues. P. chabaudi malaria induces imap38 expression almost exclusively in the spleen but not in other lymphoid organs. Parasite lysates are able to induce imap38 in the spleen, but not in spleen cells ex vivo. Activation of spleen cells by LPS and other stimuli is not sufficient to induce imap38. Inducibility of imap38 requires signals from both parasites and the intact spleen, and it is controlled by genes of that non-H-2 background, which also controls development of protective immunity against P. chabaudi malaria.

Experimental trypanosomiasis of natural hybrids between house mouse subspecies

This study characterises the extent of the susceptibility to parasites (first demonstrated with helminths) of hybrids between Mus musculus domesticus and Mus musculus musculus. Experimental infections with Trypanosoma musculi of M. m. domesticus, M. m. musculus and their natural hybrids have been performed to compare their level of resistance/susceptibility. It appears that contrary to the results with helminths, hybrid mice present the same level of resistance/susceptibility to the trypanosome as M. m. musculus and M. m. domesticus individuals. This result is interpreted in the light of the modalities of host parasite interactions and leads us to hypothesise on the role of parasitism in the evolution of the house mouse hybrid zone.