Senescent BALB/c mice are able to develop resistance to Leishmania major infection

Chronically hypertensive transgenic mice expressing human AT1R haplotype-I exhibit increased susceptibility to Francisella tularensis

Age-related illnesses, including hypertension and accompanying metabolic disorders, compromise immunity and exacerbate infection-associated fatalities. Renin-angiotensin system (RAS) is the key mechanism that controls blood pressure. Upregulation of RAS through angiotensin receptor type 1 (AT1R), a G-protein coupled receptor, contributes to the pathophysiological consequences leading to vascular remodeling, hypertension, and end-organ damage. Genetic variations that increase the expression of human AT1R may cause the above pathological outcomes associated with hypertension. Previously we have shown that our chronically hypertensive transgenic (TG) mice containing the haplotype-I variant (Hap-I, hypertensive genotype) of human AT1R (hAT1R) gene are more prone to develop the metabolic syndrome-related disorders as compared to the TG mice containing the haplotype-II variant (Hap-II, normotensive genotype). Since aging and an increased risk of hypertension can impact multiple organ systems in a complex manner, including susceptibility to various infections, the current study investigated the susceptibility and potential effect of acute bacterial infection using a Gram-negative intracellular bacterial pathogen, Francisella tularensis in our hAT1R TG mice. Our results show that compared to Hap-II, F. tularensis-infected aged Hap-I TG mice have significantly higher mortality post-infection, higher bacterial load and lung pathology, elevated inflammatory cytokines and altered gene expression profile favoring hypertension and inflammation. Consistent with worsened phenotype in aged Hap-I mice post-Francisella infection, gene expression profiles from their lungs revealed significantly altered expression of more than 1,400 genes. Furthermore, bioinformatics analysis identified genes associated with RAS and IFN-γ pathways regulating blood pressure and inflammation. These studies demonstrate that haplotype-dependent over-expression of the hAT1R gene leads to enhanced susceptibility and lethality due to F. tularensis LVS infection, which gets aggravated in aged animals. Clinically, these findings will help in exploring the role of AT1R-induced hypertension and enhanced susceptibility to infection-related respiratory diseases.

Ageing impairs protective immunity and promotes susceptibility to murine visceral leishmaniasis

It is well accepted that the impact of diseases is generally more detrimental in elderly individuals than in younger ones. Changes in the immune system due to ageing can directly affect the ability to respond effectively to infections and may contribute to the higher morbidities and mortalities in the elderly population. Leishmaniasis is a complex of clinically unique diseases caused by obligate intracellular protozoa belonging to genus Leishmania, wherein visceral leishmaniasis (VL) is the most severe form and is fatal if left untreated. In this study, aged mice (72 weeks old) presented increased susceptibility to L. infantum infection compared to younger mice (4–6-week-old), with notable parasitism in both the spleen and liver, as well as exhibiting hepatosplenomegaly. A pronounced inflammatory profile was observed in the aged-infected mice, with excessive production of TNF-α and nitrite, along with diminished IFN-γ production and reduced proliferative capacity of T cells (assessed by expression of the Ki67 marker). Additionally, both CD4+ and CD8+ T cells from the aged-infected mice presented increased expression of the inhibitory receptors PD-1 and KLRG1 that strongly correlated with the parasitism found in the liver and spleen of this group. Overall, the data reported in this study suggests for the first time that ageing may negatively impact the VL outcome and provides a perspective for new therapeutic strategies involving manipulation of immunosenescence features against Leishmania infection.

Age-dependent rise in IFN-γ competence undermines effective type 2 responses to nematode infection

The efficient induction of type 2 immune responses is central to the control of helminth infections. Previous studies demonstrated that strong Th1 responses driven by intracellular pathogens as well as a bias for type 1 activity in senescent mice impedes the generation of Th2 responses and the control of intestinal nematode infections. Here, we show that the spontaneous differentiation of Th1 cells and their expansion with age restrains type 2 immunity to infection with the small intestinal nematode H. polygyrus much earlier in life than previously anticipated. This includes the more extensive induction of IFN-γ competent, nematode-specific Th2/1 hybrid cells in BALB/c mice older than three months compared to younger animals. In C57BL/6 mice, Th1 cells accumulate more rapidly at steady state, translating to elevated Th2/1 differentiation and poor control of parasite fitness in primary infections experienced at a young age. Blocking of early IFN-γ and IL-12 signals during the first week of nematode infection leads to sharply decreased Th2/1 differentiation and promotes resistance in both mouse lines. Together, these data suggest that IFN-γ competent, type 1 like effector cells spontaneously accumulating in the vertebrate host progressively curtail the effectiveness of anti-nematode type 2 responses with rising host age.

Host immune response against leishmaniasis and parasite persistence strategies: A review and assessment of recent research

Leishmaniasis, a neglected parasitic disease caused by a unicellular protozoan of the genus Leishmania, is transmitted through the bite of a female sandfly. The disease remains a major public health problem and is linked to tropical and subtropical regions, with an endemic picture in several regions, including East Africa, the Mediterranean basin and South America. The different causative species display a diversity of clinical presentations; therefore, the immunological data on leishmaniasis are both scarce and controversial for the different forms and infecting species of the parasite. The present review highlights the main immune parameters associated with leishmaniasis that might contribute to a better understanding of the pathogenicity of the parasite and the clinical outcomes of the disease. Our aim was to provide a concise overview of the immunobiology of the disease and the factors that influence it, as this knowledge may be helpful in developing novel chemotherapeutic and vaccine strategies.

Strain specificities in influence of ageing on germinal centre reaction to inactivated influenza virus antigens in mice: Sex-based differences

Considering variability in vaccine responsiveness across human populations, in respect to magnitude and quality, and importance of vaccines in the elderly, the influence of recipient genetic background on the kinetics of age-related changes in the serum IgG antibody responses to seasonal trivalent inactivated split-virus influenza bulk (TIV) was studied in BALB/c and C57BL/6 mice showing quantitative and qualitative differences in this responses in young adult ages. With ageing the total serum IgG response to influenza viruses declined, in a strain-specific manner, so the strain disparity observed in young adult mice (the greater magnitude of IgG response in BALB/c mice) disappeared in aged mice. However, the sexual dimorphisms in this response (more prominent in females of both strains) remained in aged ones. The strain-specific differences in age-related decline in the magnitude of IgG response to TIV correlated with the number of germinal centre (GC) B splenocytes. The age-related decline in GC B cell number was consistent with the decrease in the proliferation of B cells and CD4+ cells in splenocyte cultures upon restimulation with TIV. Additionally, the age-related decrease in the magnitude of IgG response correlated with the increase in follicular T regulatory (fTreg)/follicular T helper (fTh) and fTreg/GC B splenocyte ratios (reflecting decrease in fTh and GC B numbers without changes in fTreg number), and the frequency of CD4+ splenocytes producing IL-21, a key factor in balancing the B cell and fTreg cell activity. With ageing the avidity of virus influenza-specific antibody increased in females of both strains. Moreover, ageing affected IgG2a/IgG1 and IgG2c/IgG1 ratios (reflecting Th1/Th2 balance) in male BALB/c mice and female C57BL/6 mice, respectively. Consequently, differently from young mice exhibiting the similar ratios in male and female mice, in aged female mice of both strains IgG2a(c)/IgG1 ratios were shifted towards a less effective IgG1 response (stimulated by IL-4 cytokines) compared with males. The age-related alterations in IgG subclass profiles in both strains correlated with those in IFN-γ/IL-4 production level ratio in splenocyte cultures restimulated with TIV. These findings stimulate further research to formulate sex-specific strategies to improve efficacy of influenza vaccine in the elderly.

Tuberculosis in the elderly: Why inflammation matters

Growing old is associated with an increase in the basal inflammatory state of an individual and susceptibility to many diseases, including infectious diseases. Evidence is growing to support the concept that inflammation and disease susceptibility in the elderly is linked. Our studies focus on the infectious disease tuberculosis (TB), which is caused by Mycobacterium tuberculosis (M.tb), a pathogen that infects approximately one fourth of the world's population. Aging is a major risk factor for developing TB, and inflammation has been strongly implicated. In this review we will discuss the relationship between inflammation in the lung and susceptibility to develop and succumb to TB in old age. Further understanding of the relationship between inflammation, age, and M.tb will lead to informed decisions about TB prevention and treatment strategies that are uniquely designed for the elderly.

Could age and aging change the host response to systemic parasitic infections? A systematic review of preclinical evidence

The impact of age and aging in the evolution of systemic parasitic infections remains poorly understood. We conducted a systematic review from preclinical models of Chagas disease, leishmaniasis, malaria, sleeping sickness and toxoplasmosis. From a structured and comprehensive search in electronic databases, 29 studies were recovered and included in the review. Beyond the characteristics of the experimental models, parasitological and immunological outcomes, we also discussed the quality of current evidence. Our findings indicated that throughout aging, parasitemia and mortality were consistently reduced in Chagas disease and malaria, but were similar or increased in leishmaniasis and highly variable in toxoplasmosis. While a marked humoral response in older animals was related to the anti-T. cruzi protective phenotype, cellular responses mediated by a polarized Th1 phenotype were associated with a more effective defense against Plasmodium infection. Conversely, in leishmaniasis, severe infections and high mortality rates were potentially related to attenuation of humoral response and an imbalance between Th1 and Th2 phenotypes. Due to the heterogeneous parasitological outcomes and limited immunological data, the role of aging on toxoplasmosis evolution remains unclear. From a detailed description of the methodological bias, more controlled researches could avoid the systematic reproduction of inconsistent and poorly reproducible experimental designs.

Live Attenuated Leishmania donovani Centrin Knock Out Parasites Generate Non-inferior Protective Immune Response in Aged Mice against Visceral Leishmaniasis

Background

Visceral leishmaniasis (VL) caused by the protozoan parasite Leishmania donovani causes severe disease. Age appears to be critical in determining the clinical outcome of VL and at present there is no effective vaccine available against VL for any age group. Previously, we showed that genetically modified live attenuated L. donovani parasites (LdCen-/-) induced a strong protective innate and adaptive immune response in young mice. In this study we analyzed LdCen-/- parasite mediated modulation of innate and adaptive immune response in aged mice (18 months) and compared to young (2 months) mice.

Methodology

Analysis of innate immune response in bone marrow derived dendritic cells (BMDCs) from both young and aged mice upon infection with LdCen-/- parasites, showed significant enhancement of innate effector responses, which consequently augmented CD4⁺ Th1 cell effector function compared to LdWT infected BMDCs in vitro. Similarly, parasitized splenic dendritic cells from LdCen-/- infected young and aged mice also revealed induction of proinflammatory cytokines (IL-12, IL-6, IFN-γ and TNF) and subsequent down regulation of anti-inflammatory cytokine (IL-10) genes compared to LdWT infected mice. We also evaluated in vivo protection of the LdCen-/- immunized young and aged mice against virulent L. donovani challenge. Immunization with LdCen-/- induced higher IgG2a antibodies, lymphoproliferative response, pro- and anti-inflammatory cytokine responses and stimulated splenocytes for heightened leishmanicidal activity associated with nitric oxide production in young and aged mice. Furthermore, upon virulent L. donovani challenge, LdCen-/- immunized mice from both age groups displayed multifunctional Th1-type CD4 and cytotoxic CD8 T cells correlating to a significantly reduced parasite burden in the spleen and liver compared to naïve mice. It is interesting to note that even though there was no difference in the LdCen-/- induced innate response in dendritic cells between aged and young mice; the adaptive response specifically in terms of T cell and B cell activation in aged animals was reduced compared to young mice which correlated with less protection in old mice compared to young mice.

Conclusions

Taken together, LdCen-/- immunization induced a significant but diminished host protective response in aged mice after challenge with virulent L. donovani parasites compared to young mice.

Visceral leishmaniasis (VL) is caused by the protozoan parasite Leishmania donovani. There is no effective vaccine available against VL for any age group and importantly, there are no previous studies regarding immune responses against experimental Leishmania vaccines tested in aged animals. We have reported earlier that immunization with a live attenuated L. donovani parasites (LdCen-/-) induced protective immune response in young animals viz, mice, hamsters and dogs. In this study we analyzed LdCen-/- mediated modulation of innate and adaptive responses in aged mice and compared to young mice. We observed that LdCen-/- infected dendritic cells from young and aged mice resulted in enhanced innate effector functions compared to LdWT parasites both in vitro and in vivo. Further, upon virulent challenge, LdCen-/- immunized young and aged mice displayed protective Th1 immune response which correlated with a significantly reduced parasite burden in the visceral organs compared with naïve challenged mice. Although there was no difference in the LdCen-/- induced dendritic cell response between aged and young mice; adaptive response in aged was reduced, compared to young which correlated with less protection in aged compared to young mice. This study supports the potential use of LdCen-/- as vaccine candidate across all age groups against VL.

Ultraviolet B efficacy in improving antileishmanial effects of silver nanoparticles

OBJECTIVES

Cutaneous Leishmaniasis (CL) is a parasitic disease caused by various species of the flagellated protozoan, Leishmania. Regardless of the numerous studies, there are still serious challenges in the treatment of CL. This study aimed at evaluating the influence of a low dose ultraviolet B (UVB) radiation along with silver nanoparticles (AgNPs) on a mouse model of CL induced by Leishmania major.

MATERIALS AND METHODS

L. major promastigotes (MRHO/IR/75/ER) were extracted from infected mice spleens. Two months after subcutaneous injection of 2×10(6) promastigotes into the footpad of BALB/c mice, when the lesions were developed, the animals were divided into 4 groups including one control group and three study groups: AgNPs, UVB and UVB plus AgNPs. Spleen parasite burden was assessed on day 40 after the first treatment. The data were analyzed by Instat, Elida and SPSS 16 software programs.

RESULTS

The results showed the highest pronounced inhibitory effect in the group receiving AgNPs plus UVB. In addition, a significant difference was obtained between the group receiving AgNPs alone and the one with combinational therapy. The findings on parasite burden showed a significant difference between the control group and other treatment groups.

CONCLUSION

It could be suggested that UVB in the presence of AgNPs, by inhibiting the spread of CL lesions and reducing the rate of visceral progression of the disease, provides a serious anti-leishmanial effect.

Mice with heterozygous deficiency of manganese superoxide dismutase (SOD2) have a skin immune system with features of "inflamm-aging"

Dendritic cells (DC) are central in regulating skin immunity. Immunosenescence is associated with a chronic inflammatory state. Little is known about the contribution of DC to "inflamm-aging". When determining langerhans cell (LC) numbers, we found a 60 % reduction of LC in aged epidermis. Reactive oxygen species(ROS) are linked with aging. The mitochondrial manganese superoxide dismutase (SOD2) is in the first line of antioxidant defense. We investigated the function of DC from SOD2 heterozygous mice (SOD2+/-) and found that at 4 months of age LC numbers are not altered, but activated LC have impaired expression of MHC-II and CD44. Immature SOD2+/- DC produced increased proinflammatory IL-6 and chemokines CXCL1 and CXCL2. Upon challenge SOD2+/- DC accumulated ROS. When activating SOD2+/- DC by LPS they less efficiently upregulated MHC-II, CD86 and CD44. Surprisingly, in vivo contact hypersensitivity (CHS) was enhanced in SOD2+/- mice although SOD2+/- DC were less potent in stimulating wt T cells. However, SOD2+/- T cells showed increased proliferation, even when stimulated with SOD2+/- DC, possibly explaining the increased CHS. Our findings suggest that SOD2 is a molecular candidate in the regulation of "inflamm-aging" conveying both immunosuppressive and proinflammatory signals through alteration of DC and T cell functions.

Induction of an anti-inflammatory human monocyte subtype is a unique property of glucocorticoids, but can be modified by IL-6 and IL-10

Glucocorticoids (GC) are the most widely used immunosuppressive agents in clinical medicine. Recently we showed that GC enhance survival of human monocytes and induce a specific anti-inflammatory monocyte subtype which actively induces resolution of inflammation. We now investigated if cytokines IL-4, IL-6 and IL-10, which, like GC, have mostly anti-inflammatory effects on macrophages, would have GC-like effects also on monocytes. Human monocytes were stimulated with either cytokine, GC or combination thereof, and resulting effects on apoptosis, adherence, migration, phagocytosis, ROS production and cell surface phenotype were determined. We found that IL-4, IL-6, and IL-10 had either less or different effects on various anti-inflammatory functions of monocytes compared to GC. As such, IL-4 and IL-6 alone did not delay apoptosis while IL-10 even enhanced it. However, IL-6 or IL-10 increased GC-mediated protection from apoptosis when applied together with GC. Thus, the potential of GC to induce anti-inflammatory human monocytes is unique and not mimicked by the investigated cytokines. However, IL-6 and IL-10 amplify GC-induced anti-inflammatory and pro-resolution mechanisms by enhancing survival of GC-induced monocytes and thus sustaining their function. This combined effect of GC and cytokines could be important for the physiological switch from amplification towards resolution phase of inflammation.

Aging enhances the production of reactive oxygen species and bactericidal activity in peritoneal macrophages by upregulating classical activation pathways

Maintenance of macrophages in their basal state and their rapid activation in response to pathogen detection are central to the innate immune system, acting to limit nonspecific oxidative damage and promote pathogen killing following infection. To identify possible age-related alterations in macrophage function, we have assayed the function of peritoneal macrophages from young (3-4 months) and aged (14-15 months) Balb/c mice. In agreement with prior suggestions, we observe age-dependent increases in the extent of recruitment of macrophages into the peritoneum, as well as ex vivo functional changes involving enhanced nitric oxide production under resting conditions that contribute to a reduction in the time needed for full activation of senescent macrophages following exposure to lipopolysaccharides (LPS). Further, we observe enhanced bactericidal activity following Salmonella uptake by macrophages isolated from aged Balb/c mice in comparison with those isolated from young animals. Pathways responsible for observed phenotypic changes were interrogated using tandem mass spectrometry, which identified age-dependent increases in levels of proteins linked to immune cell pathways under basal conditions and following LPS activation. Immune pathways upregulated in macrophages isolated from aged mice include proteins critical to the formation of the immunoproteasome. Detection of these latter proteins is dramatically enhanced following LPS exposure for macrophages isolated from aged animals; in comparison, the identification of immunoproteasome subunits is insensitive to LPS exposure for macrophages isolated from young animals. Consistent with observed global changes in the proteome, quantitative proteomic measurements indicate that there are age-dependent abundance changes involving specific proteins linked to immune cell function under basal conditions. LPS exposure selectively increases the levels of many proteins involved in immune cell function in aged Balb/c mice. Collectively, these results indicate that macrophages isolated from old mice are in a preactivated state that enhances their sensitivities to LPS exposure. The hyper-responsive activation of macrophages in aged animals may act to minimize infection by general bacterial threats that arise due to age-dependent declines in adaptive immunity. However, this hypersensitivity and the associated increase in the level of formation of reactive oxygen species are likely to contribute to observed age-dependent increases in the level of oxidative damage that underlie many diseases of the elderly.

Role of proteinase-activated receptor-2 in anti-bacterial and immunomodulatory effects of interferon-γ on human neutrophils and monocytes

Recent studies show that proteinase-activated receptor-2 (PAR(2)) contributes to the development of inflammatory responses. However, investigations into the precise role of PAR(2) activation in the anti-microbial defence of human leucocytes are just beginning. We therefore evaluated the contribution of PAR(2) to the anti-microbial response of isolated human innate immune cells. We found that PAR(2) agonist, acting alone, enhances phagocytosis of Staphylococcus aureus and killing of Escherichia coli by human leucocytes, and that the magnitude of the effect is similar to that of interferon-γ (IFN-γ). However, co-application of PAR(2) -cAP and IFN-γ did not enhance the phagocytic and bacteria-killing activity of leucocytes beyond that triggered by either agonist alone. On the other hand, IFN-γ enhances PAR(2) agonist-induced monocyte chemoattractant protein 1 (MCP-1) secretion by human neutrophils and monocytes. Furthermore, phosphoinositide-3 kinase and janus kinase molecules are involved in the synergistic effect of PAR(2) agonist and IFN-γ on MCP-1 secretion. Our findings suggest a potentially protective role of PAR(2) agonists in the anti-microbial defence established by human monocytes and neutrophils.

Hormone levels are associated with clinical markers and cytokine levels in human localized cutaneous leishmaniasis

Leishmaniasis is a serious health problem in several parts of the world, and localized cutaneous leishmaniasis (LCL) is the most frequent presentation of the tegumentary form of this disease cluster. Clinical presentations of leishmaniasis are influenced by both parasite and host factors, with emphasis on the host immune response. Alterations in plasma hormone levels have been described in many infections, and changes in hormone levels could be related to an imbalanced cytokine profile. In the present work, we evaluated a group of patients with LCL to determine changes in plasma hormone levels (cortisol, DHEA-S, estradiol, prolactin and testosterone) and their association with clinical markers of disease (lesion size, dose used to reach cure and time to cure) and with cytokines produced by PBMC stimulated by SLA (IFN-γ, IL-10 and TNF-α). Individuals with LCL exhibited lower plasma levels of DHEA-S, prolactin and testosterone compared with sex-matched controls, whereas levels of cortisol and estradiol were similar between patients and controls. Plasma levels of cortisol, estradiol or prolactin positively correlated with at least one clinical parameter. Cortisol and prolactin levels exhibited a negative correlation with levels of IFN-γ, whereas no correlation was observed with IL-10 or TNF-α levels. A decrease in DHEA-S levels was observed in male LCL patients when compared to male healthy controls. No other differences between the sexes were observed. Our results indicate a role for neuroendocrine regulation that restricts Th1 responses in human LCL. It is possible that, although impairing parasite killing, such neuroimmunomodulation may contribute to limiting tissue damage.

Attenuated response of aged mice to respiratory Francisella novicida is characterized by reduced cell death and absence of subsequent hypercytokinemia

Background

Pneumonia and pulmonary infections are major causes of mortality among the growing elderly population. Age associated attenuations of various immune parameters, involved with both innate and adaptive responses are collectively known as immune senescence. These changes are likely to be involved with differences in host susceptibility to disease between young and aged individuals.

Methodology/Principal Findings

The objective of this study was to assess potential age related differences in the pulmonary host response in mice to the Gram-negative respiratory pathogen, Francisella novicida. We intranasally infected mice with F. novicida and compared various immune and pathological parameters of the pulmonary host response in both young and aged mice.

Conclusions/Significance

We observed that 20% of aged mice were able to survive an intranasal challenge with F. novicida while all of their younger cohorts died consistently within 4 to 6 days post infection. Further experiments revealed that all of the aged mice tested were initially able to control bacterial replication in the lungs as well as at distal sites of replication compared with young mice. In addition, the small cohort of aged survivors did not progress to a severe sepsis syndrome with hypercytokinemia, as did all of the young adult mice. Finally, a lack of widespread cell death in potential aged survivors coupled with a difference in cell types recruited to sites of infection within the lung confirmed an altered host response to Francisella in aged mice.

Aged mice display an altered pulmonary host response to Francisella tularensis live vaccine strain (LVS) infections

Aging is a complex phenomenon that has been shown to affect many organ systems including the innate and adaptive immune systems. The current study was designed to examine the potential effect of immunosenescence on the pulmonary immune response using a Francisella tularensis live vaccine strain (LVS) inhalation infection model. F. tularensis is a Gram-negative intracellular pathogen that can cause a severe pneumonia. In this study both young (8-12 week old) and aged (20-24 month old) mice were infected intranasally with LVS. Lung tissues from young and aged mice were used to assess pathology, recruitment of immune cell types and cytokine expression levels at various times post infection. Bacterial burdens were also assessed. Interestingly, the lungs of aged animals harbored fewer organisms at early time points of infection (day 1, day 3) compared with their younger counterparts. In addition, only aged animals displayed small perivascular aggregates at these early time points that appeared mostly mononuclear in nature. However, the kinetics of infiltrating polymorphonuclear neutrophils (PMNs) and increased cytokine levels measured in the bronchial alveolar lavage fluid (BALF) were delayed in infected aged animals relative to young infected animals with neutrophils appearing at day 5 post infection (PI) in the aged animals as opposed to day 3 PI in the young infected animals. Also evident were alterations in the ratios of mononuclear to PMNs at distinct post infection times. The above evidence indicates that aged mice elicit an altered immune response in the lung to respiratory F. tularensis LVS infections compared to their younger counterparts.

In vivo optical imaging of cellular inflammatory response in granuloma formation using fluorescence-labeled macrophages

Near-infrared imaging such as fluorescence reflectance imaging (FRI) and fluorescence-mediated tomography (FMT) yields high signal-to-noise ratios (SNRs) and should thus be well suited for cell-tracking studies. Extravasation of monocytes or macrophages (Ms) is one of the earliest events in inflammation. The purpose of this study was to assess whether FRI and FMT allow for the visualization and quantification of early inflammatory processes by tracing the migration of fluorescence-labeled murine Ms in a cutaneous granuloma model.

METHODS

Ms were labeled with a membrane-selective carbocyanine dye (1,1-dioctadecyl-3,3,3,3-tetramethylindotricarbocyanine iodide [DiR]). Cellular viability and function (nitric oxide production, phagocytosis, adherence) were assessed in vitro. Local inflammation was induced in mice by the subcutaneous injection of polyacrylamide gel pellets including or excluding a strong inflammatory stimulus (lipopolysaccharide). Labeled Ms were injected intravenously, and FRI and FMT were performed up to 7 d. SNRs were calculated for the pellets, and the 3-dimensional distribution of Ms was assessed using FMT. Cells were harvested from gel pellets and analyzed by flow cytometry.

RESULTS

DiR labeling did not affect cell viability or cell function. FRI revealed the migration of labeled Ms into gel pellets and the homing of Ms to different body compartments. The lipopolysaccharide-containing pellets exhibited significantly higher SNRs than did pellets without lipopolysaccharide. FMT showed that Ms distributed mainly in the periphery of the pellets. The cellular infiltrates extracted from the harvested pellets revealed the presence of approximately 10%-23% DiR-positive Ms-expressing typical markers, confirming the transendothelial migration of injected Ms.

CONCLUSION

The tagging of Ms with DiR allows the noninvasive tracking of inflammatory cells for several days in vivo. FRI and FMT are versatile techniques to monitor and quantify cellular inflammatory responses in vivo.

Effects of estrogen replacement therapy on estrogen receptor expression and immunoregulatory cytokine secretion in surgically induced menopausal women

To investigate the effect of oral and transdermal estrogen replacement therapy (ERT) on the expression of different estrogen receptor (ER) subtypes and the secretion of immunoregulatory cytokines, we performed a clinical investigation on previously healthy women who had undergone a total hysterectomy and bilateral salpingo-oopherectomy. These women were randomly distributed into two groups: an oral ERT group and transdermal ERT group. Before and after ERT, the serum levels of estradiol (E2) and follicle stimulating hormone (FSH) were measured, ERalpha and ERbeta expression of peripheral blood T lymphocytes was tested, and secretion of specific immunoregulatory cytokines (IFNgamma, IL-2 and IL-4) by T lymphocytes was examined. Our results confirm that for both groups, the serum E2 level was increased after ERT (P<0.01) and the serum FSH level was decreased after ERT (P<0.01), with no significant difference in hormone levels between the two groups. ERalpha expression by T lymphocytes was significantly higher after ERT than before (P<0.01) in both groups. Levels of type 1 cytokines (IL-2 and IFNgamma), which were secreted by T helper 1 (Th1), after ERT were substantially decreased. The level of type 2 cytokine (IL-4), which were secreted by T helper 2 (Th2), was significantly increased after ERT (P<0.01 for the oral group and P<0.05 for the transdermal group). In summary, both oral and transdermal ERT increased serum E2 levels, decreased serum FSH levels and relieved the effects of peri-menopausal symptoms. These data suggest that both oral and transdermal ERT act to improve the balance of Th1/Th2 cytokines by the effects of estrogen potentially acting in T lymphocytes mainly through ERalpha.

Interleukin-12 is sufficient to promote antigen-independent interferon-gamma production by CD8 T cells in old mice

Numerous functional defects have been identified in naive T cells from aged mice, including deficiencies in proliferation, cytokine production and signal transduction. It is well documented that the ratio of naïve to memory T cells significantly decreases with age resulting in the majority of T cells from aged hosts expressing activated/memory T-cell markers (CD44(hi)), yet it is unclear whether T cells with a CD44(hi) phenotype in aged hosts are functionally equivalent to T cells with a similar phenotype in young hosts. We have identified a population of CD44(hi) CD8 T cells in old mice that are capable of secreting interferon-gamma (IFN-gamma) in response to interleukin-12 (IL-12) stimulation. This occurred in the absence of T-cell receptor engagement, a function that was not observed in CD8 T cells from young mice. This phenotype was associated with increased IL-12 receptor beta2 gene expression and IL-12 induced signal transducer and activator of transcription 4 (STAT-4) activation, even when CD8 T-cell numbers from young and old mice were normalized for CD44(hi) expression. Furthermore, we demonstrate that IL-12-induced STAT-4 activation was required for T helper type 1 (Th1) cytokine-induced IFN-gamma production in CD8 T cells. These data illustrate that old mice possess a specialized subset of CD44(hi) CD8 T cells with an enhanced responsiveness to IL-12, enabling these cells to produce substantial amounts of IFN-gamma in response to Th1 cytokine stimulation. We have therefore identified a functional difference in the populations of CD44(hi) CD8 T cells from young and old mice, and believe that understanding age-associated immunological changes is essential for helping the elderly combat deadly diseases.

Functional regulatory T cells accumulate in aged hosts and promote chronic infectious disease reactivation

Declines in immune function are well described in the elderly and are considered to contribute significantly to the disease burden in this population. Regulatory T cells (T(regs)), a CD4(+) T cell subset usually characterized by high CD25 expression, control the intensity of immune responses both in rodents and humans. However, because CD25 expression does not define all T(regs), especially in aged hosts, we characterized T(regs) by the expression of FOXP3, a transcription factor crucial for T(reg) differentiation and function. The proportion of FOXP3(+)CD4(+) T(regs) increased in the blood of the elderly and the lymphoid tissues of aged mice. The expression of functional markers, such as CTLA-4 and GITR, was either preserved or increased on FOXP3(+) T(regs) from aged hosts, depending on the tissue analyzed. In vitro depletion of peripheral T(regs) from elderly humans improves effector T cell responses in most subjects. Importantly, T(regs) from old FoxP3-GFP knock-in mice were suppressive, exhibiting a higher level of suppression per cell than young T(regs). The increased proportion of T(regs) in aged mice was associated with the spontaneous reactivation of chronic Leishmania major infection in old mice, likely because old T(regs) efficiently suppressed the production of IFN-gamma by effector T cells. Finally, in vivo depletion of T(regs) in old mice attenuated disease severity. Accumulation of functional T(regs) in aged hosts could therefore play an important role in the frequent reactivation of chronic infections that occurs in aging. Manipulation of T(reg) numbers and/or activity may be envisioned to enhance the control of infectious diseases in this fragile population.

The absence of cutaneous lymph nodes results in a Th2 response and increased susceptibility to Leishmania major infection in mice

Lymph nodes (LNs) are important sentinel organs where antigen-presenting cells interact with T cells to induce adaptive immune responses. In cutaneous infection of mice with Leishmania major, resistance depends on the induction of a T-helper-cell-1 (Th1)-mediated cellular immune response in draining, peripheral LNs. We investigated whether draining, peripheral LNs are absolutely required for resistance against L. major infection. We investigated the course of experimental leishmaniasis in wild-type (wt) mice lacking peripheral LNs (pLNs), which we generated by in utero blockade of membrane-bound lymphotoxin, and in mice lacking pLNs or all LNs due to genetic deletion of lymphotoxin ligands or receptors. wt mice of the resistant C57BL/6 strain without local skin-draining LNs were still able to generate specific T-cell responses, but this yielded Th2 cells. This switch to a Th2 response resulted in severe systemic infection. We also confirmed these results with mice lacking pLNs due to genetic depletion of lymphotoxin-beta. The complete absence of LNs due to a genetic depletion of the lymphotoxin-beta receptor also resulted in a marked deterioration of disease and a Th2 response. Thus, in the absence of pLNs, an L. major-specific Th2 response is induced in the remaining secondary lymphoid organs, such as the spleen and non-skin-draining LNs. This indicates a critical requirement for pLNs to induce protective Th1 immunity and suggests that whether Th1 or Th2 priming to the same antigen occurs depends on the site of the primary antigen recognition.

Galectin-9 suppresses the generation of Th17, promotes the induction of regulatory T cells, and regulates experimental autoimmune arthritis

The effects of galectin-9 on a mouse collagen-induced arthritis (CIA) model were assessed to clarify whether galectin-9 suppresses CIA by regulating T cell immune responses. Galectin-9 suppressed CIA in a dose-dependent manner, and such suppression was observed even when treatment was started on 7 days after the booster, indicating its preventive and therapeutic effects. Galectin-9 induced the decreased levels of pro-inflammatory cytokines, IL-17, IL-12, and IFNgamma in the joint. Galectin-9 induced the decreased number of CD4(+) TIM-3(+) T cells in peripheral blood. Galectin-9-deficient mice became susceptible to CIA may be by increased number of CD4(+) TIM-3(+) T cells and decreased number of Treg cells. We further found that galectin-9 induces differentiation of naive T cells to Treg cells, and it suppresses differentiation to Th17 cells in vitro. The present results suggested that galectin-9 ameliorates CIA by suppressing the generation of Th17, promoting the induction of regulatory T cells.

Mucosal adjuvant activity of flagellin in aged mice

We evaluated the ability of flagellin, a highly effective mucosal adjuvant in mice and non-human primates, to promote mucosal innate and adaptive immunity in aged mice. We found that intratracheal instillation of flagellin induced a stronger respiratory innate response in aged mice than in young mice, and that intranasal instillation of flagellin was equally effective at triggering recruitment of T and B lymphocytes to the draining lymph nodes of young and aged mice. Intranasal immunization of aged mice with flagellin and the Yersinia pestis protein F1 promoted specific IgG and IgA production, but at lower levels and lower avidities than in young mice. Although intranasal instillation of flagellin and F1 antigen increased germinal center formation and size in young mice, it did not do so in aged mice. Our findings are consistent with the conclusion that flagellin can promote adaptive immune responses in aged mice, but at a less robust level than in young mice.

Outcome and immune responses after Brucella abortus infection in young adult and aged mice

Aging results in a general waning of immunity and enhanced susceptibility to many intracellular pathogens. However, in some instances, aging is accompanied by alternative immune responses that can be equal to, or even more effective, than those of young adults. Brucella spp. are intracellular bacteria and important human and animal pathogens, but there are no data regarding the effect of age on host defense in brucellosis. Young or old adult mice (DBA/2 or BALB/c) were infected with either an attenuated B. abortus strain that over-expressed the Brucella superoxide dismutase (strain RB51-SOD) or a fully virulent strain (strain 2308). Survival, organism burden in the spleen, and immune responses were assessed. All young adult and aged mice survived infection with RB51-SOD (up to 6 x 10(8) cfu) or strain 2308 (up to 8 x 10(8) cfu). Old mice had a lower organism burden in the spleen than young adult mice five or more weeks after infection. Antibody and cytokine responses were Th1-focused in young adult mice, but Th-mixed in older mice, including evidence of the newly defined Th17 subtype immune response. Immunization with the RB51-SOD strain provided protection vs. strain 2308 challenge in young and aged BALB/c, but only young adult DBA/2 mice. Thus, clinical outcomes of Brucella infection in aged mice are equal or superior to those of young adult mice; immune responses in older mice are less-Th1 specific suggesting alternate pathways may contribute to host defense vs. Brucella in aged mice.

Vitamin D receptor signaling contributes to susceptibility to infection with Leishmania major

We have previously reported that 1alpha,25-dihydroxyvitamin D3 (1alpha,25(OH)2D3) can selectively suppress key functions of interferon-gamma (IFN-gamma) activated macrophages. To further explore this mechanism for its relevance in vivo, we investigated an infection model that crucially depends on the function of IFN-gamma activated macrophages, the infection with the intracellular protozoan Leishmania major. 1Alpha,25(OH)2D3 treatment of L. major infected macrophages demonstrated a vitamin D receptor (Vdr) dependent inhibition of macrophage killing activity. Further analysis showed that this was a result of decreased production of nitric oxide by 1alpha,25(OH)2D3-treated macrophages due to Vdr-dependent up-regulation of arginase 1 expression, which overrides NO production by Nos2. When analyzing the course of infection in vivo, we found that Vdr-knockout (Vdr-KO) mice were more resistant to L. major infection than their wild-type littermates. This result is in agreement with an inhibitory influence of 1alpha,25(OH)2D3 on the macrophage mediated host defense. Further investigation showed that Vdr-KO mice developed an unaltered T helper cell type 1 (Th1) response on infection as indicated by normal production of IFN-gamma by CD4+ and CD8+ T cells. Therefore, we propose that the absence of 1alpha,25(OH)2D3-mediated inhibition of macrophage microbicidal activity in Vdr-KO mice results in increased resistance to Leishmania infection.

Age-influenced population kinetics and immunological responses of Leishmania donovani in hamsters

Susceptibility of animals to infections depends upon various factors including sex and age of the host, which plays a pivotal role. In this communication, we have investigated the "intake" of Leishmania donovani infection in young (3-4 weeks old) and adult (15-16 weeks old) golden hamsters. The splenic parasite load in young hamsters on day 15 post infection (p.i.) was 54 +/- 4 amastigotes/100 macrophage nuclei and increased to 106.3 +/- 3.5 on day 30 p.i. However, adult group showed 2.2-(P < 0.001) and 1.75-fold (P < 0.001) lesser parasite burden on these days, respectively. But as the disease progresses further, differences in parasite burden become less significant, as revealed by comparable levels of parasite loads at 2 months p.i. Spleen weight measurements correspond to the above observations. In the young group, the levels of antileishmanial antibody rise two and 4.5 times on days 15 and 30 p.i., respectively, as compared to only 1.3 and 2.3 times increase in their respective adult counterparts. However, after 2 months of infection both groups recorded analogous (12-fold) rise in antibody levels. Both mitogenic and antigenic responses in adult hamsters were less suppressed compared to young hamsters on days 15 and 30 p.i. However, both groups exhibited highly suppressed cell-mediated immune (CMI) responses after 2 months of infection. These findings implicate that age of the host may influence the susceptibility and resistance to Leishmania infection.

Age dependent increase in early resistance of mice to Mycobacterium tuberculosis is associated with an increase in CD8 T cells that are capable of antigen independent IFN-gamma production

The lungs of naïve 18-month-old mice contain an abundant resident population of CD8 T cells that express typical markers of memory, express elevated levels of Th1 cytokine receptors on their surface, and are capable of non-specific IFN-gamma production in response to a Th1 cytokine cocktail. In this study we characterize this population of CD8 T cells in the lungs and spleens of mice with increasing age. In general, the proportion of CD8 T cells expressing markers of memory and Th1 cytokine receptors increased with age. The enhanced ability of CD8 T cells to produce IFN-gamma in an antigen independent manner followed this pattern as well, beginning to increase between 6 and 12 months of age. Interestingly, the phenotypic and functional age-related changes in CD8 T cells were also associated with a progressive age-related increase in early resistance to Mycobacterium tuberculosis. Taken together, these data suggest that as mice age a population of memory CD8 T cells, that are capable of contributing to innate immune responses to M. tuberculosis, gradually emerges and could be relevant for developing strategies to enhance immunity in the elderly.

Glucocorticoids induce differentiation of a specifically activated, anti-inflammatory subtype of human monocytes

Monocytes and macrophages may either promote or down-regulate inflammatory reactions depending on their state of activation. The effects of glucocorticoids (GCs), the most widely used immunosuppressive drugs, on monocytes are currently not well defined. By analyzing the GC-induced expression pattern in human monocytes by microarray technology, we identified for the first time GC-dependent regulation of 133 genes, including anti-inflammatory molecules such as adenosine A3 receptor, CD1d, and IL-1 receptor II. The results were independently confirmed by real-time polymerase chain reaction (PCR) and flow cytometry. Functional clustering of GC-regulated genes indicated induction of monocytic properties such as phagocytosis and motility as well as repression of adhesion, apoptosis, and oxidative burst. These predictions were confirmed by independent functional assays. GCs up-regulate fMLP receptors and specifically promote chemotaxis to this chemoattractant. Furthermore, GCs promote survival of an anti-inflammatory monocytic phenotype in inflammatory reactions, probably by inhibition of apoptosis because of oxidative stress. GCs limit tissue damage because of induction of antioxidative properties and high capacity for phagocytosis of proinflammatory agents. Thus, GC treatment did not cause a global suppression of monocytic effector functions but results in differentiation of a specific anti-inflammatory phenotype which seems to be actively involved in resolution of inflammatory reactions.

Th1 cytokines facilitate CD8-T-cell-mediated early resistance to infection with Mycobacterium tuberculosis in old mice

Numerous immunological defects begin to emerge as an individual ages, the consequence of which is heightened susceptibility to infectious diseases. Despite this decline in immune function, old mice display an early transient resistance to Mycobacterium tuberculosis infection in the lung, which is dependent on CD8 T cells and gamma interferon (IFN-gamma) production. In this study, we investigated the mechanism of resistance by examining the CD8-T-cell phenotype and function in old naïve and M. tuberculosis-infected mice. Pulmonary CD8 T cells from naïve old mice expressed cell surface markers of memory in addition to receptors for several Th1 cytokines. Stimulation of lung cells from naïve old mice with a combination of Th1 cytokines (interleukin-2 [IL-2], IL-12, and IL-18) resulted in nonspecific production of IFN-gamma by memory CD8 T cells. Following aerosol infection with M. tuberculosis, the lungs of old mice contained significantly more IL-12, IL-18, and IFN-gamma than the lungs of young mice contained. Together, these data demonstrate that the increased and early production of Th1 cytokines in the lungs of M. tuberculosis-infected old mice, in combination with CD8 T cells that can nonspecifically produce IFN-gamma, leads to transient control of M. tuberculosis growth in the lungs of old mice. Further characterization of this mechanism should provide essential information regarding the aging immune system and should contribute to the development of novel strategies to decrease the morbidity and mortality of the aging population associated with infectious diseases.

Leashing Leishmania. Some old mice fight parasitic infection better than young mice do

Most of the people who die from flu each winter are older than 65. But a new study suggests that sometimes age bolsters, rather than cripples, the immune system. In at least one strain of mice, geriatric rodents resist a parasitic skin infection better than youngsters do. The finding highlights the convoluted changes that time imparts on the immune system, although researchers don't yet know how the finding relates to human health.