CD25 Appears Non Essential for Human Peripheral Treg Maintenance In Vivo

Background

IL-2 has been reported to be critical for peripheral T_reg survival in mouse models. Here, we examined T_reg maintenance in a series of paediatric liver transplant recipients who received basiliximab, a therapeutic anti-CD25 monoclonal antibody.

Methodology/Principal Findings

FoxP3⁺ CD4 T cells were analyzed by flow cytometry before liver grafting and more than 9 months later. We found that in vivo CD25 blockade did not lead to T_reg depletion: the proportion of FoxP3⁺ cells among CD4 T cells and the level of FoxP3 expression were both unchanged. IL-2Rβ expression was enhanced in FoxP3⁺ cells both before and after basiliximab treatment, while the level of IL-2Rγ expression was similar in T_regs and non-T_regs. No significant change in the weak or absent expression of IL-7Rα and IL-15Rα expression on FoxP3⁺ cells was observed. Although the proportion of FoxP3⁺ cells among CD4 T cells did not vary, food allergies occurred more rapidly after liver grafting in patients who received basiliximab, raising questions as to T_reg functionality in vivo in the absence of functional CD25.

Conclusions

CD25 appears non essential for human T_reg peripheral maintenance in vivo. However, our results raise questions as to T_reg functionality after therapeutic CD25 targeting.     

Transiently Reduced PI3K/Akt Activity Drives the Development of Regulatory Function in Antigen-Stimulated Na?ve T-Cells

Regulatory T-cells (T_regs) are central for immune homeostasis and divided in thymus-derived natural T_regs and peripherally induced iT_reg. However, while phenotype and function of iT_regs are well known, a remarkable lack exists in knowledge about signaling mechanisms leading to their generation from naïve precursors in peripheral tissues. Using antigen specific naïve T-cells from mice, we investigated CD4+ CD25+ FoxP3- iT_reg induction during antigen-specific T-cell receptor (TCR) stimulation with weak antigen presenting cells (APC). We show that early signaling pathways such as ADAM-17-activation appeared similar in developing iT_reg and effector cells (T_eff) and both initially shedded CD62-L. But iT_reg started reexpressing CD62-L after 24 h while T_eff permanently downmodulated it. Furthermore, between 24 and 72 hours iT_reg presented with significantly lower phosphorylation levels of Akt-S473 suggesting lower activity of the PI3K/Akt-axis. This was associated with a higher expression of the Akt hydrophobic motif-specific phosphatase PHLPP1 in iT_reg. Importantly, the lack of costimulatory signals via CD28 from weak APC was central for the development of regulatory function in iT_reg but not for the reappearance of CD62-L. Thus, T-cells display a window of sensitivity after onset of TCR triggering within which the intensity of the PI3K/Akt signal controls entry into either effector or regulatory pathways.     

T-cell specific defect in expression of the NTPDase CD39 as a biomarker for lupus

Regulatory T cells (T_regs) are critical for maintenance of peripheral tolerance via suppression of T-cell responses, and absence of T_regs results in autoimmunity. The role of aberrations in the T_reg pool for the development of systemic lupus erythematosus (SLE, lupus) remains uncertain. T_reg-mediated generation of adenosine, dependent on the ectonucleotidase CD39, is an important mechanism for suppression of T-cell responses. We tested whether decreases in numbers of T_regs, and specifically CD39-expressing T_regs, are associated with human lupus. We studied 15 SLE patients, six patients with rheumatoid arthritis (RA) and 24 healthy controls. T_reg phenotypic markers, including CD39 expression, were studied by flow cytometry. Varying numbers of sorted T_regs cells were co-cultured with responder T (T_resp) cells, with proliferation assessed by ³H-thymidine incorporation. The proportion of T_regs as defined by Foxp3⁺ CD25^+high CD127^−/low was similar in lupus and control populations. CD39-expressing T_regs comprised 37 ± 13% of the T_reg population in healthy controls and 36 ± 21% in lupus subjects using nonsteroidal immunosuppressants to control active disease, but was nearly absent in five of six lupus subjects with minimally active disease. In contrast to healthy controls and lupus subjects without the CD39 defect, in SLE subjects with the CD39 defect, adenosine-dependent T_reg-mediated suppression was nearly absent. These results suggest that functional defects in T_regs, rather than reduced T_reg numbers, are important for the loss of peripheral tolerance in lupus. Presentation of this defect may serve as a biomarker for untreated disease.     

Suppression of Glomerulonephritis in NZB/NZW Lupus Prone Mice by Adoptive Transfer of Ex Vivo Expanded Regulatory T Cells

Systemic lupus erythematosus (SLE) is an autoimmune disease of unknown cause characterized by expansion of autoreactive lymphocytes. Regulatory T cells (T_regs) are a component of the normal immune system and contribute to the maintenance of peripheral tolerance. T_reg abnormalities have been associated with several autoimmune diseases and there is interest in the role of T_regs in SLE. We previously demonstrated that transfer of expanded CD4⁺CD25⁺CD62L^HI T_regs slows the development of lupus in (NZBxNZW)F₁ (B/W) mice. However in the absence of T_reg specific surface antigens, cell purification remains a compromise between the breadth and purity of the population isolated. Importantly, purified populations always contain Foxp3⁻ effector T cells (T_effs) that theoretically could exacerbate autoimmunity in the recipient. Here we explore the impact of transferring the more comprehensive, but less pure T_reg subset defined by CD4⁺CD25⁺ expression on development of murine lupus. All cells were FACS sorted and expanded prior to adoptive transfer. Development of proteinuria and survival were measured. We found that exogenous expansion of CD4⁺CD25⁺ cells produced a population containing 70–85% CD4⁺Foxp3⁺T_regs. Expanded T_regs had higher CTLA-4 and Foxp3 expression, increased in vitro suppression capacity, and prolonged in vivo survival as compared to freshly isolated cells. Adoptive transfer of expanded CD4⁺CD25⁺ T_regs inhibited the onset of glomerulonephritis and prolonged survival in mice. Importantly the population of T_eff contained within the adoptively transferred cells had reduced survival and proliferation capacity as compared to either co-transferred T_regs or transferred T_effs expanded in the absence of T_regs. These studies demonstrate that adoptive transfer of expanded CD4⁺CD25⁺Foxp3⁺T_regs has the capacity to inhibit the onset of murine lupus and that this capacity is significant despite transfer of co-cultured T_eff cells. These data indicate that when co-expanded with regulatory T cells, exogenously activated T_effs from autoimmune patients may not pose a significant risk of promoting disease.     

Natural Regulatory T Cells in Malaria: Host or Parasite Allies?

Plasmodium falciparum malaria causes 500 million clinical cases with approximately one million deaths each year. After many years of exposure, individuals living in endemic areas develop a form of clinical immunity to disease known as premunition, which is characterised by low parasite burdens rather than sterilising immunity. The reason why malaria parasites persist under a state of premunition is unknown but it has been suggested that suppression of protective immunity might be a mechanism leading to parasite persistence. Although acquired immunity limits the clinical impact of infection and provides protection against parasite replication, experimental evidence indicates that cell-mediated immune responses also result in detrimental inflammation and contribute to the aetiology of severe disease. Thus, an appropriate regulatory balance between protective immune responses and immune-mediated pathology is required for a favourable outcome of infection. As natural regulatory T (T_reg) cells are identified as an immunosuppressive lineage able to modulate the magnitude of effector responses, several studies have investigated whether this cell population plays a role in balancing protective immunity and pathogenesis during malaria. The main findings to date are summarised in this review and the implication for the induction of pathogenesis and immunity to malaria is discussed.     

Modulation of immune responses by Plasmodium falciparum infection in asymptomatic children living in the endemic region of Mbita,western Kenya

Individuals living in malaria endemic areas become clinically immune after multiple re-infections over time and remain infected without apparent symptoms. However, it is unclear why a long period is required to gain clinical immunity to malaria, and how such immunity is maintained. Although malaria infection is reported to induce inhibition of immune responses, studies on asymptomatic individuals living in endemic regions of malaria are relatively scarce. We conducted a cross-sectional study of immune responses in asymptomatic school children aged 4–16 years living in an area where Plasmodium falciparum and Schistosoma mansoni infections are co-endemic in Kenya. Peripheral blood mononuclear cells were subjected to flow cytometric analysis and cultured to determine proliferative responses and cytokine production. The proportions of cellular subsets in children positive for P. falciparum infection at the level of microscopy were comparable to the negative children, except for a reduction in central memory-phenotype CD8⁺ T cells and natural killer cells. In functional studies, the production of cytokines by peripheral blood mononuclear cells in response to P. falciparum crude antigens exhibited strong heterogeneity among children. In addition, production of IL-2 in response to anti-CD3 and anti-CD28 monoclonal antibodies was significantly reduced in P. falciparum-positive children as compared to -negative children, suggesting a state of unresponsiveness. These data suggest that the quality of T cell immune responses is heterogeneous among asymptomatic children living in the endemic region of P. falciparum, and that the responses are generally suppressed by active infection with Plasmodium parasites.     

Commitment to the Regulatory T Cell Lineage Requires CARMA1 in the Thymus but Not in the Periphery

Regulatory T (T_reg) cells expressing forkhead box P3 (Foxp3) arise during thymic selection among thymocytes with modestly self-reactive T cell receptors. In vitro studies suggest Foxp3 can also be induced among peripheral CD4⁺ T cells in a cytokine dependent manner. T_reg cells of thymic or peripheral origin may serve different functions in vivo, but both populations are phenotypically indistinguishable in wild-type mice. Here we show that mice with a Carma1 point mutation lack thymic CD4⁺Foxp3⁺ T_reg cells and demonstrate a cell-intrinsic requirement for CARMA1 in thymic Foxp3 induction. However, peripheral Carma1-deficient T_reg cells could be generated and expanded in vitro in response to the cytokines transforming growth factor beta (TGFβ) and interleukin-2 (IL-2). In vivo, a small peripheral T_reg pool existed that was enriched at mucosal sites and could expand systemically after infection with mouse cytomegalovirus (MCMV). Our data provide genetic evidence for two distinct mechanisms controlling regulatory T cell lineage commitment. Furthermore, we show that peripheral T_reg cells are a dynamic population that may expand to limit immunopathology or promote chronic infection.     

Lifelong dynamics of human CD4CD25 regulatory T cells: Insights from in vivo data and mathematical modeling

Despite their limited proliferation capacity, regulatory T cells (T_regs) constitute a population maintained over the entire lifetime of a human organism. The means by which T_regs sustain a stable pool in vivo are controversial. Using a mathematical model, we address this issue by evaluating several biological scenarios of the origins and the proliferation capacity of two subsets of T_regs: precursor CD4⁺CD25⁺CD45RO⁻ and mature CD4⁺CD25⁺CD45RO⁺ cells. The lifelong dynamics of T_regs are described by a set of ordinary differential equations, driven by a stochastic process representing the major immune reactions involving these cells. The model dynamics are validated using data from human donors of different ages. Analysis of the data led to the identification of two properties of the dynamics: (1) the equilibrium in the CD4⁺CD25⁺FoxP3⁺T_regs population is maintained over both precursor and mature T_regs pools together, and (2) the ratio between precursor and mature T_regs is inverted in the early years of adulthood. Then, using the model, we identified three biologically relevant scenarios that have the above properties: (1) the unique source of mature T_regs is the antigen-driven differentiation of precursors that acquire the mature profile in the periphery and the proliferation of T_regs is essential for the development and the maintenance of the pool; there exist other sources of mature T_regs, such as (2) a homeostatic density-dependent regulation or (3) thymus- or effector-derived T_regs, and in both cases, antigen-induced proliferation is not necessary for the development of a stable pool of T_regs. This is the first time that a mathematical model built to describe the in vivo dynamics of regulatory T cells is validated using human data. The application of this model provides an invaluable tool in estimating the amount of regulatory T cells as a function of time in the blood of patients that received a solid organ transplant or are suffering from an autoimmune disease.     

Acquisition of growth-inhibitory antibodies against blood-stage Plasmodium falciparum

Background

Antibodies that inhibit the growth of blood-stage Plasmodium falciparum may play an important role in acquired and vaccine-induced immunity in humans. However, the acquisition and activity of these antibodies is not well understood.

Methods

We tested dialysed serum and purified immunoglobulins from Kenyan children and adults for inhibition of P. falciparum blood-stage growth in vitro using different parasite lines. Serum antibodies were measured by ELISA to blood-stage parasite antigens, extracted from P. falciparum schizonts, and to recombinant merozoite surface protein 1 (42 kDa C-terminal fragment, MSP1-42).

Results

Antibodies to blood-stage antigens present in schizont protein extract and to recombinant MSP1-42 significantly increased with age and were highly correlated. In contrast, growth-inhibitory activity was not strongly associated with age and tended to decline marginally with increasing age and exposure, with young children demonstrating the highest inhibitory activity. Comparison of growth-inhibitory activity among samples collected from the same population at different time points suggested that malaria transmission intensity influenced the level of growth-inhibitory antibodies. Antibodies to recombinant MSP1-42 were not associated with growth inhibition and high immunoglobulin G levels were poorly predictive of inhibitory activity. The level of inhibitory activity against different isolates varied.

Conclusions

Children can acquire growth-inhibitory antibodies at a young age, but once they are acquired they do not appear to be boosted by on-going exposure. Inhibitory antibodies may play a role in protection from early childhood malaria.     

The control of CD4<Superscript>+</Superscript>CD25<Superscript>+</Superscript>Foxp3<Superscript>+</Superscript>regulatory T cell survival

   

CD4⁺CD25⁺Foxp3⁺ regulatory T (T_reg) cells are believed to play an important role in suppressing autoimmunity and maintaining peripheral tolerance. How their survival is regulated in the periphery is less clear. Here we show that T_reg cells express receptors for gamma chain cytokines and are dependent on an exogenous supply of these cytokines to overcome cytokine withdrawal apoptosis in vitro. This result was validated in vivo by the accumulation of T_reg cells in Bim^-/- and Bcl-2 tg mice which have arrested cytokine deprivation apoptosis. We also found that CD25 and Foxp3 expression were down-regulated in the absence of these cytokines. CD25⁺ cells from Scurfy mice do not depend on cytokines for survival demonstrating that Foxp3 increases their dependence on cytokines by suppressing cytokine production in T_reg cells. Our study reveals that the survival of T_reg cells is strictly dependent on cytokines and cytokine producing cells because they do not produce cytokines. Our study thus, demonstrates that different gamma chain cytokines regulate T_reg homeostasis in the periphery by differentially regulating survival and proliferation. These findings may shed light on ways to manipulate T_reg cells that could be utilized for their therapeutic applications.     

Apoptosis of CD4+CD25high T Cells in Type 1 Diabetes May Be Partially Mediated by IL-2 Deprivation

Background

Type 1 diabetes (T1D) is a T-cell mediated autoimmune disease targeting the insulin-producing pancreatic β cells. Naturally occurring FOXP3⁺CD4⁺CD25^high regulatory T cells (T_regs) play an important role in dominant tolerance, suppressing autoreactive CD4⁺ effector T cell activity. Previously, in both recent-onset T1D patients and β cell antibody-positive at-risk individuals, we observed increased apoptosis and decreased function of polyclonal T_regs in the periphery. Our objective here was to elucidate the genes and signaling pathways triggering apoptosis in T_regs from T1D subjects.

Principal Findings

Gene expression profiles of unstimulated T_regs from recent-onset T1D (n = 12) and healthy control subjects (n = 15) were generated. Statistical analysis was performed using a Bayesian approach that is highly efficient in determining differentially expressed genes with low number of replicate samples in each of the two phenotypic groups. Microarray analysis showed that several cytokine/chemokine receptor genes, HLA genes, GIMAP family genes and cell adhesion genes were downregulated in T_regs from T1D subjects, relative to control subjects. Several downstream target genes of the AKT and p53 pathways were also upregulated in T1D subjects, relative to controls. Further, expression signatures and increased apoptosis in T_regs from T1D subjects partially mirrored the response of healthy T_regs under conditions of IL-2 deprivation. CD4⁺ effector T-cells from T1D subjects showed a marked reduction in IL-2 secretion. This could indicate that prior to and during the onset of disease, T_regs in T1D may be caught up in a relatively deficient cytokine milieu.

Conclusions

In summary, expression signatures in T_regs from T1D subjects reflect a cellular response that leads to increased sensitivity to apoptosis, partially due to cytokine deprivation. Further characterization of these signaling cascades should enable the detection of genes that can be targeted for restoring T_reg function in subjects predisposed to T1D.     

Atopic dermatitis induces the expansion of thymus‐derived regulatory T cells exhibiting a Th2‐like phenotype in mice

Atopic dermatitis (AD) is a widespread inflammatory skin disease with an early onset, characterized by pruritus, eczematous lesions and skin dryness. This chronic relapsing disease is believed to be primarily a result of a defective epidermal barrier function associated with genetic susceptibility, immune hyper‐responsiveness of the skin and environmental factors. Although the important role of abnormal immune reactivity in the pathogenesis of AD is widely accepted, the role of regulatory T cells (T_regs) remains elusive. We found that the T_reg population is expanded in a mouse model of AD, i.e. mice topically treated with vitamin D3 (VitD). Moreover, mice with AD‐like symptoms exhibit increased inducible T‐cell costimulator (ICOS)‐, cytotoxic T‐lymphocyte antigen‐4 (CTLA‐4)‐ and Glycoprotein‐A repetitions predominant receptor (GARP)‐expressing T_regs in skin‐draining lymph nodes. Importantly, the differentiation of T_regs into thymus‐derived T_regs is favoured in our mouse model of AD. Emigrated skin‐derived dendritic cells are required for T_reg induction and Langerhans cells are responsible for the biased expansion of thymus‐derived T_regs. Intriguingly, thymus‐derived T_regs isolated from mice with AD‐like symptoms exhibit a Th2 cytokine profile. Thus, AD might favour the expansion of pathogenic T_regs able to produce Th2 cytokines and to promote the disease instead of alleviating symptoms.     

Improved In Vitro Culture of Plasmodium falciparum Permits Establishment of Clinical Isolates with Preserved Multiplication,Invasion and Rosetting Phenotypes

To be able to robustly propagate P. falciparum at optimal conditions in vitro is of fundamental importance for genotypic and phenotypic studies of both established and fresh clinical isolates. Cryo-preserved P. falciparum isolates from Ugandan children with severe or uncomplicated malaria were investigated for parasite phenotypes under different in vitro growth conditions or studied directly from the peripheral blood. The parasite cultures showed a minimal loss of parasite-mass and preserved percentage of multiple infected pRBCs to that in peripheral blood, maintained adhesive phenotypes and good outgrowth and multiplication rates when grown in suspension and supplemented with gas. In contrast, abnormal and greatly fluctuating levels of multiple infections were observed during static growth conditions and outgrowth and multiplication rates were inferior. Serum, as compared to Albumax, was found necessary for optimal presentation of PfEMP1 at the pRBC surface and/or for binding of serum proteins (immunoglobulins). Optimal in vitro growth conditions of P. falciparum therefore include orbital shaking (50 rev/min), human serum (10%) and a fixed gas composition (5% O₂, 5% CO₂, 90% N₂). We subsequently established 100% of 76 frozen patient isolates and found rosetting with schizont pRBCs in every isolate (>26% schizont rosetting rate). Rosetting during schizogony was often followed by invasion of the bound RBC as seen by regular and time-lapse microscopy as well as transmission electron microscopy. The peripheral parasitemia, the level of rosetting and the rate of multiplication correlated positively to one another for individual isolates. Rosetting was also more frequent with trophozoite and schizont pRBCs of children with severe versus uncomplicated malaria (p<0.002; p<0.004). The associations suggest that rosetting enhances the ability of the parasite to multiply within the human host.     

The Ratio of Monocytes to Lymphocytes in Peripheral Blood Correlates with Increased Susceptibility to Clinical Malaria in Kenyan Children

Background

Plasmodium falciparum malaria remains a major cause of illness and death in sub-Saharan Africa. Young children bear the brunt of the disease and though older children and adults suffer relatively fewer clinical attacks, they remain susceptible to asymptomatic P. falciparum infection. A better understanding of the host factors associated with immunity to clinical malaria and the ability to sustain asymptomatic P. falciparum infection will aid the development of improved strategies for disease prevention.

Methods and Findings

Here we investigate whether full differential blood counts can predict susceptibility to clinical malaria among Kenyan children sampled at five annual cross-sectional surveys. We find that the ratio of monocytes to lymphocytes, measured in peripheral blood at the time of survey, directly correlates with risk of clinical malaria during follow-up. This association is evident among children with asymptomatic P. falciparum infection at the time the cell counts are measured (Hazard ratio (HR)  =  2.7 (95% CI 1.42, 5.01, P  =  0.002) but not in those without detectable parasitaemia (HR  =  1.0 (95% CI 0.74, 1.42, P  =  0.9).

Conclusions

We propose that the monocyte to lymphocyte ratio, which is easily derived from routine full differential blood counts, reflects an individual''s capacity to mount an effective immune response to P. falciparum infection.     

The Quantity and Quality of African Children's IgG Responses to Merozoite Surface Antigens Reflect Protection against Plasmodium falciparum Malaria

Background

Antibodies, particularly cytophilic IgG subclasses, with specificity for asexual blood stage antigens of Plasmodium falciparum, are thought to play an important role in acquired immunity to malaria. Evaluating such responses in longitudinal sero-epidemiological field studies, allied to increasing knowledge of the immunological mechanisms associated with anti-malarial protection, will help in the development of malaria vaccines.

Methods and Findings

We conducted a 1-year follow-up study of 305 Senegalese children and identified those resistant or susceptible to malaria. In retrospective analyses we then compared post-follow-up IgG responses to six asexual-stage candidate malaria vaccine antigens in groups of individuals with clearly defined clinical and parasitological histories of infection with P. falciparum. In age-adjusted analyses, children resistant to malaria as well as to high-density parasitemia, had significantly higher IgG1 responses to GLURP and IgG3 responses to MSP2 than their susceptible counterparts. Among those resistant to malaria, high anti-MSP1 IgG1 levels were associated with protection against high-density parasitemia. To assess functional attributes, we used an in vitro parasite growth inhibition assay with purified IgG. Samples from individuals with high levels of IgG directed to MSP1, MSP2 and AMA1 gave the strongest parasite growth inhibition, but a marked age-related decline was observed in these effects.

Conclusion

Our data are consistent with the idea that protection against P. falciparum malaria in children depends on acquisition of a constellation of appropriate, functionally active IgG subclass responses directed to multiple asexual stage antigens. Our results suggest at least two distinct mechanisms via which antibodies may exert protective effects. Although declining with age, the growth inhibitory effects of purified IgG measurable in vitro reflected levels of anti-AMA1, -MSP1 and -MSP2, but not of anti-GLURP IgG. The latter could act on parasite growth via indirect parasiticidal pathways.     

Brown Adipose Tissue Harbors a Distinct Sub-Population of Regulatory T Cells

Regulatory T (T_reg) cells are critical determinants of both immune responses and metabolic control. Here we show that systemic ablation of T_reg cells compromised the adaptation of whole-body energy expenditure to cold exposure, correlating with impairment in thermogenic marker gene expression and massive invasion of pro-inflammatory macrophages in brown adipose tissue (BAT). Indeed, BAT harbored a unique sub-set of T_reg cells characterized by a unique gene signature. As these T_reg cells respond to BAT activation upon cold exposure, this study defines a BAT-specific T_reg sub-set with direct implications for the regulation of energy homeostasis in response to environmental stress.     

TGF-β Signalling Is Required for CD4+ T Cell Homeostasis But Dispensable for Regulatory T Cell Function

TGF-β is widely held to be critical for the maintenance and function of regulatory T (T_reg) cells and thus peripheral tolerance. This is highlighted by constitutive ablation of TGF-β receptor (TR) during thymic development in mice, which leads to a lethal autoimmune syndrome. Here we describe that TGF-β–driven peripheral tolerance is not regulated by TGF-β signalling on mature CD4⁺ T cells. Inducible TR2 ablation specifically on CD4⁺ T cells did not result in a lethal autoinflammation. Transfer of these TR2-deficient CD4⁺ T cells to lymphopenic recipients resulted in colitis, but not overt autoimmunity. In contrast, thymic ablation of TR2 in combination with lymphopenia led to lethal multi-organ inflammation. Interestingly, deletion of TR2 on mature CD4⁺ T cells does not result in the collapse of the T_reg cell population as observed in constitutive models. Instead, a pronounced enlargement of both regulatory and effector memory T cell pools was observed. This expansion is cell-intrinsic and seems to be caused by increased T cell receptor sensitivity independently of common gamma chain-dependent cytokine signals. The expression of Foxp3 and other regulatory T cells markers was not dependent on TGF-β signalling and the TR2–deficient T_reg cells retained their suppressive function both in vitro and in vivo. In summary, absence of TGF-β signalling on mature CD4⁺ T cells is not responsible for breakdown of peripheral tolerance, but rather controls homeostasis of mature T cells in adult mice.     

Local induction of immunosuppressive CD8+ T cells in the gut-associated lymphoid tissues

Background

In contrast to intestinal CD4⁺ regulatory T cells (T_regs), the generation and function of immunomodulatory intestinal CD8⁺ T cells is less well defined. To dissect the immunologic mechanisms of CD8⁺ T cell function in the mucosa, reactivity against hemagglutinin (HA) expressed in intestinal epithelial cells of mice bearing a MHC class-I-restricted T-cell-receptor specific for HA was studied.

Methodology and Principal Findings

HA-specific CD8⁺ T cells were isolated from gut-associated tissues and phenotypically and functionally characterized for the expression of Foxp3⁺ and their suppressive capacity. We demonstrate that intestinal HA expression led to peripheral induction of HA-specific CD8⁺Foxp3⁺ T cells. Antigen-experienced CD8⁺ T cells in this transgenic mouse model suppressed the proliferation of CD8⁺ and CD4⁺ T cells in vitro. Gene expression analysis of suppressive HA-specific CD8⁺ T cells revealed a specific up-regulation of CD103, Nrp1, Tnfrsf9 and Pdcd1, molecules also expressed on CD4⁺ T_reg subsets. Finally, gut-associated dendritic cells were able to induce HA-specific CD8⁺Foxp3⁺ T cells.

Conclusion and Significance

We demonstrate that gut specific antigen presentation is sufficient to induce CD8⁺ T_regs in vivo which may maintain intestinal homeostasis by down-modulating effector functions of T cells.     

The Effect of Daily Co-Trimoxazole Prophylaxis on Natural Development of Antibody-Mediated Immunity against P. falciparum Malaria Infection in HIV-Exposed Uninfected Malawian Children

Background and Objectives

Co-trimoxazole prophylaxis, currently recommended in HIV-exposed, uninfected (HEU) children as protection against opportunistic infections, also has some anti-malarial efficacy. We determined whether daily co-trimoxazole prophylaxis affects the natural development of antibody-mediated immunity to blood-stage Plasmodium falciparum malaria infection.

Methods

Using an enzyme-linked immunosorbent assay, we measured antibodies to 8Plasmodium falciparum antigens (AMA-1, MSP-1₁₉, MSP-3, PfSE, EBA-175RII, GLURP R0, GLURP R2 and CSP) in serum samples from 33 HEU children and 31 HIV-unexposed, uninfected (HUU) children, collected at 6, 12 and 18 months of age.

Results

Compared to HIV-uninfected children, HEU children had significantly lower levels of specific IgG against AMA-1 at 6 months (p = 0.001), MSP-1₁₉ at 12 months (p = 0.041) and PfSE at 6 months (p = 0.038), 12 months (p = 0.0012) and 18 months (p = 0.0097). No differences in the IgG antibody responses against the rest of the antigens were observed between the two groups at all time points. The breadth of specificity of IgG response was reduced in HEU children compared to HUU children during the follow up period.

Conclusions

Co-trimoxazole prophylaxis seems to reduce IgG antibody responses to P. falciparum blood stage antigens, which could be as a result of a reduction in exposure of those children under this regime. Although antibody responses were regarded as markers of exposure in this study, further studies are required to establish whether these responses are correlated in any way to clinical immunity to malaria.