T cell responses to bacterial infection

Inclusion of a dual signal sequence enhances the immunogenicity of a novel viral vectored vaccine against the capsular group B meningococcus

BACKGROUND

Disease caused by the capsular group B meningococcus (MenB) is the leading cause of infectious death in UK infants. A novel adenovirus-based vaccine encoding the MenB factor H binding protein (fHbp) with an N-terminal dual signal sequence induces high titres of protective antibody after a single dose in mice. A panel of N-terminal signal sequence variants were created to assess the contribution of components of this sequence to transgene expression kinetics of the encoded antigen from mammalian cells and the resultant effect on immunogenicity of fHbp.

RESULTS

The full-length signal sequence (FL SS) resulted in superior early antigen expression compared with the panel of variants, as measured by flow cytometry and confocal imaging, and supported higher bactericidal antibody levels against the expressed antigen in mouse sera < 6 weeks post-immunisation than the licensed four component MenB vaccine. The FL SS also significantly increased antigen-specific T cell responses against other adenovirus-encoded bacterial antigens in mice.

CONCLUSIONS

These findings demonstrate that the FL SS enhances immunogenicity of the encoded antigen, supporting its inclusion in other viral vectored bacterial antigen transgenes.

Contribution of IL-38 in Lung Immunity during Pseudomonas Aeruginosa-induced Pneumonia

OBJECTIVE

Interleukin-38 (IL-38), a new type of cytokine, is involved in processes such as tissue repair, inflammatory response, and immune response. However, its function in pneumonia caused by Pseudomonas aeruginosa (P. aeruginosa) is still unclear.

METHODS

In this study, we detected circulating IL-38 and cytokines such as IL-1β, IL-6, IL-17A, TNF-α, IL-8, and IL-10 in adults affected by early stage pneumonia caused by P. aeruginosa. Collected clinical data of these patients, such as the APACHE II score, levels of PCT, and oxygenation index when they entering the ICU. Using P. aeruginosa-induced pneumonia WT murine model to evaluate the effect of IL-38 on Treg differentiation, cell apoptosis, survival, tissue damage, inflammation, and bacterial removal.

RESULTS

In clinical research, although IL-38 is significantly increased during the early stages of clinical P. aeruginosa pneumonia, the concentration of IL-38 in the serum of patients who died with P. aeruginosa pneumonia was relatively lower than that of surviving patients. It reveals IL-38 may insufficiently secreted in patients who died with P. aeruginosa pneumonia. Besides, the serum IL-38 level of patients with P. aeruginosa pneumonia on the day of admission to the ICU showed significantly positive correlations with IL-10 and the PaO2/FiO2 ratio but negative correlations with IL-1β, IL-6, IL-8, IL-17, TNF-α, APACHE II score, and PCT In summary, IL-38 might be a molecule for adjuvant therapy in P. aeruginosa pneumonia. In experimental animal models, first recombinant IL-38 improved survival, whereas anti-IL-38 antibody reduced survival in the experimental pneumonia murine model. Secondly, IL-38 exposure reduced the inflammatory response, as suggested by the lung injury, and reduced cytokine levels (IL-1β, IL-6, IL- 17A, TNF-α, and IL-8, but not IL-10). It also increased bacterial clearance and reduced cell apoptosis in the lungs. Furthermore, IL-38 was shown to reduce TBK1 expression in vitro when naive CD4+ T lymphocytes were differentiated to Tregs and played a protective role in P. aeruginosa pneumonia.

CONCLUSIONS

To summarize, the above findings provide additional insights into the mechanism of IL-38 in the treatment of P. aeruginosa pneumonia.

T Cell Immunity to Bacterial Pathogens: Mechanisms of Immune Control and Bacterial Evasion

The human body frequently encounters harmful bacterial pathogens and employs immune defense mechanisms designed to counteract such pathogenic assault. In the adaptive immune system, major histocompatibility complex (MHC)-restricted αβ T cells, along with unconventional αβ or γδ T cells, respond to bacterial antigens to orchestrate persisting protective immune responses and generate immunological memory. Research in the past ten years accelerated our knowledge of how T cells recognize bacterial antigens and how many bacterial species have evolved mechanisms to evade host antimicrobial immune responses. Such escape mechanisms act to corrupt the crosstalk between innate and adaptive immunity, potentially tipping the balance of host immune responses toward pathological rather than protective. This review examines the latest developments in our knowledge of how T cell immunity responds to bacterial pathogens and evaluates some of the mechanisms that pathogenic bacteria use to evade such T cell immunosurveillance, to promote virulence and survival in the host.

Curcumin nanoparticles are a promising anti-bacterial and anti-inflammatory agent for treating periprosthetic joint infections

Background

Periprosthetic joint infections (PJIs) have a high incidence of recurrence after total joint replacement and are difficult to treat by debridement or antibiotic treatment. Curcumin is a natural product with anti-inflammatory and anti-bacterial properties. The low bioactivity of curcumin in water restricts its clinical application. Curcumin nanoparticles (CURN) were developed to overcome this limitation.

Methods

In this study, the therapeutic effects of CURN and their anti-inflammatory functions were investigated in a Staphylococcus aureus biofilm-induced PJIs model.

Results

CURN first attenuated the biofilm-induced expansion of myeloid-derived suppressor cells (MDSCs) and then regulated M1- and M2-phenotypic MDSC expression. Down-regulation of cytokines and reactive oxygen species was considered as the mechanism of CURN in reversing the suppression of T cell proliferation. The recovery of bone permeative destruction demonstrated that CURN enhanced therapeutic potency of vancomycin in vivo.

Conclusion

This is the first study to demonstrate that CURN may be useful for treating PJIs.

IL-12 and IL-7 synergize to control mucosal-associated invariant T-cell cytotoxic responses to bacterial infection

BACKGROUND

Bacterial respiratory tract infections and exacerbations of chronic lung diseases are commonly caused by nontypeable Haemophilus influenzae (NTHi). Cell-mediated cytotoxicity might be key to controlling infection, but the responses of NTHi-specific T-cell populations are not well understood. Mucosal-associated invariant T (MAIT) cells are a recently discovered, innate-like subset of T cells with cytotoxic function, the role of which in lung immunity is unclear.

OBJECTIVE

The aim of this study was to determine the mechanisms behind conventional T-cell and MAIT cell cytotoxic responses to NTHi.

METHODS

Human ex vivo lung explants were infected with a clinical strain of NTHi. Monocyte-derived macrophages were also infected with NTHi in vitro and cocultured with autologous T cells. Cytotoxic responses of T-cell subsets were measured by using flow cytometry.

RESULTS

We found significant upregulation of the cytotoxic markers CD107a and granzyme B in lung CD4⁺, CD8⁺, and MAIT cell populations. We show that MAIT cell cytotoxic responses were upregulated by a combination of both time-dependent antigen presentation and a novel mechanism through which IL-12 and IL-7 synergistically control granzyme B through upregulation of the IL-12 receptor.

CONCLUSIONS

Overall, our data provide evidence for a cytotoxic role of MAIT cells in the lung and highlight important differences in the control of adaptive and innate-like T-cell responses. Understanding these mechanisms might lead to new therapeutic opportunities to modulate the antibacterial response and improve clinical outcome.

Ethyl pyruvate reverses development of Pseudomonas aeruginosa pneumonia during sepsis-induced immunosuppression

Sepsis is characterized by an innate immune response and the following immune dysfunction which can increase the emergence of secondary infections. Ethyl pyruvate (EP) has multiple immunoregulation functions in several serious illnesses, such as burn injury, severe sepsis and acute respiratory syndrome. However, little data was shown the effect of EP administration on immunosuppression post-CLP and the following secondary infection. The cecal ligation and puncture (CLP) followed by the induction of Pseudomonas aeruginosa (PA) was used as a clinically relevant two-hit model of sepsis. We assessed the survival rate, lung damage and lung bacterial clearance in vehicle or EP treatment group to demonstrate the lung response to Pseudomonas aeruginosa of septic mice. Then cytokines including lung IL-6, IL-1β, IL-10 and plasma HMGB1, apoptosis of splenic immune cells and Foxp3 level on regulatory T cells (Tregs) were studied to demonstrate the mechanisms of EP administration on two-hit mice. We found that the susceptibility of septic mice to Secondary Pseudomonas aeruginosa pneumonia could be down-regulated by ethyl pyruvate treatment and the protective effects of EP may via decreasing lung IL-10 and plasma HMGB1 expression, inhibiting the function of Tregs and relieving the apoptosis of splenic immune cells. The "immune paralysis" post-sepsis still remains a rigorous challenge for curing sepsis, our study may aid in the development of new therapeutic strategies to this problem.

Vesicular Stomatitis Virus-Vectored Multi-Antigen Tuberculosis Vaccine Limits Bacterial Proliferation in Mice following a Single Intranasal Dose

Tuberculosis (TB) remains a serious health problem worldwide, and an urgent need exists to improve or replace the available vaccine, Mycobacterium bovis bacillus Calmette-Guérin (BCG). Most vaccination protocols adapt two or three doses to induce long-term lasting immunity. Our previous study showed that the naked DNA encoding the triple-antigen fusion TFP846 (Rv3615c-Mtb10.4-Rv2660c) induced robust T cellular immune responses accompanying four inoculations against mycobacteria infection. However, a number of compliance issues exist in some areas lacking the appropriate medical infrastructure with multiple administrations. In this study, a novel vesicular stomatitis virus expressing TFP846 (VSV-846) was developed and the immune responses elicited by VSV-846 were evaluated. We observed that intranasal delivery of VSV-846 induced a potent antigen-specific T cell response following a single dose and VSV-846 efficiently controlled bacterial growth to levels ~10-fold lower than that observed in the mock group 6 weeks post-infection in BCG-infected mice. Importantly, mice immunized with VSV-846 provided long-term protection against mycobacteria infection compared with those receiving p846 or BCG immunization. Increased memory T cells were also observed in the spleens of VSV-846-vaccinated mice, which could be a potential mechanism associated with long-term protective immune response. These findings supported the use of VSV as an antigen delivery vector with the potential for TB vaccine development.

Pathogen Stimulation History Impacts Donor-Specific CD8(+) T Cell Susceptibility to Costimulation/Integrin Blockade-Based Therapy

Recent studies have shown that the quantity of donor-reactive memory T cells is an important factor in determining the relative heterologous immunity barrier posed during transplantation. Here, we hypothesized that the quality of T cell memory also potently influences the response to costimulation blockade-based immunosuppression. Using a murine skin graft model of CD8(+) memory T cell-mediated costimulation blockade resistance, we elicited donor-reactive memory T cells using three distinct types of pathogen infections. Strikingly, we observed differential efficacy of a costimulation and integrin blockade regimen based on the type of pathogen used to elicit the donor-reactive memory T cell response. Intriguingly, the most immunosuppression-sensitive memory T cell populations were composed primarily of central memory cells that possessed greater recall potential, exhibited a less differentiated phenotype, and contained more multi-cytokine producers. These data, therefore, demonstrate that the memory T cell barrier is dependent on the specific type of pathogen infection via which the donor-reactive memory T cells are elicited, and suggest that the immune stimulation history of a given transplant patient may profoundly influence the relative barrier posed by heterologous immunity during transplantation.

Recombinant Salmonella enterica serovar Typhimurium as a vaccine vector for HIV-1 Gag

The HIV/AIDS epidemic remains a global health problem, especially in Sub-Saharan Africa. An effective HIV-1 vaccine is therefore badly required to mitigate this ever-expanding problem. Since HIV-1 infects its host through the mucosal surface, a vaccine for the virus needs to trigger mucosal as well as systemic immune responses. Oral, attenuated recombinant Salmonella vaccines offer this potential of delivering HIV-1 antigens to both the mucosal and systemic compartments of the immune system. So far, a number of pre-clinical studies have been performed, in which HIV-1 Gag, a highly conserved viral antigen possessing both T- and B-cell epitopes, was successfully delivered by recombinant Salmonella vaccines and, in most cases, induced HIV-specific immune responses. In this review, the potential use of Salmonella enterica serovar Typhimurium as a live vaccine vector for HIV-1 Gag is explored.

Overactivation of mitogen-activated protein kinase and suppression of mitofusin-2 expression are two independent events in high mobility group box 1 protein-mediated T cell immune dysfunction

High mobility group box 1 protein (HMGB1), a critical proinflammatory cytokine, has recently been identified to be an immunostimulatory signal involved in sepsis-related immune dysfunction when released extracellularly, but the potential mechanism involved remains elusive. Here, we showed that the treatment with HMGB1 in vitro inhibited T lymphocyte immune response and expression of mitofusin-2 (Mfn-2; a member of the mitofusin family) in a dose- and time-dependent manner. Upregulation of Mfn-2 expression attenuated the suppressive effect of HMGB1 on T cell immune function. The phosphorylation of both extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein kinase (MAPK) was markedly upregulated by treating with high amount of HMGB1, while pretreatment with ERK1/2 and p38 MAPK-specific inhibitors (U0126 and SB203580) could attenuate suppression of T cell immune function and nuclear factor of activated T cell (NFAT) activation induced by HMGB1, respectively. HMGB1-induced activity of ERK1/2 and p38 was not fully inhibited in the presence of U0126 or SB203580. Interestingly, overexpression of Mfn-2 had no marked effect on HMGB1-mediated activation of MAPK, but could attenuate the suppressive effect of HMGB1 on the activity of NFAT. Thus, the mechanisms involved in HMGB1-induced T cell immune dysfunction in vitro at least partly include suppression of Mfn-2 expression, overactivation of ERK1/2, p38 MAPK, and intervention of NFAT activation, while the protective effect of Mfn-2 on T cell immune dysfunction induced by HMGB1 is dependent on other signaling pathway associated with NFAT, but not MAPK. Taken together, we conclude that overactivation of MAPK and suppression of Mfn-2 expression are two independent events in HMGB1-mediated T cell immune dysfunction.

Cell-mediated immune response to epitopic MAP (multiple antigen peptide) construct of LcrV antigen of Yersinia pestis in murine model

Yersinia pestis is the causative agent of plague. Cellular immunity seems to play an important role in defense against this disease. The subunit vaccine based on V (Lcr V) antigen has been proved to be immunogenic in animals and in humans. The multiple antigen peptide (MAP), incorporating all the relevant B and T cell epitopes is highly immunogenic in mice through intranasal route of immunization in PLGA particles containing CpG-ODN as an immunoadjuvant inducing humoral and mucosal immune response. In the present study, cell-mediated immune response using same MAP was studied in murine model. Primary and memory T cell responses were studied in outbred and inbred mice immunized intranasally with MAP in the presence of two immunoadjuvants (Murabutide and CpG-ODN). All the three compartments (Spleen, Lamina propria and Peyer's patches) of the lymphoid system showed increased lymphoproliferative response. Highest lymphoproliferative response was observed especially with CpG-ODN. Cytokine profile in the culture supernatant showed highest Th(1) and Th(17) levels. FACS analysis showed expansion of both CD4(+) and CD8(+) T cells producing gamma-interferon, perforin and granzyme-B with major contribution from CD4(+) T cells.

The potential of multimer technologies in type 1 diabetes prediction strategies

Type 1 diabetes is an autoimmune disease which occurs in (human leukocyte antigen) genetically predisposed individuals as a consequence of the organ-specific immune destruction of the insulin-producing β cells in the islets of Langherans within the pancreas. Type 1 diabetes is the result of a breakdown in immune regulation that leads to expansion of autoreactive CD4+ and CD8+ T cells, autoantibody-producing B lymphocytes and activation of the innate immune system. Islet-related autoantibodies revealed themselves to be good predictors of future onset of the disease, although they are not directly pathogenetic; T cells instead play a dominant role in disease initiation and progression. In this review, we first discuss the approaches that several laboratories attempted to measure human islet autoantigen-specific T-cell function in type 1 diabetes. T-cell assays could be used in combination with standardized autoantibody screenings to improve predictive strategies. They could also help to monitor in long-term follow-up the efficacy of tolerogenic immunotherapeutic strategies when established at the onset of the disease, and help to predict the recurrence of disease. Although some recent developments based on enzyme-linked immunosorbent spot and immunoblotting techniques have been able to distinguish with good sensitivity and specificity patients from controls, T-cell results, as revealed by international workshops, were indeed largely inconclusive. Nowadays, novel technologies have been exploited that could contribute to answering the tantalizing question of identifying autoreactive T cells. We particularly focus on and discuss MHC multimer tools and emphasize the advantages they can offer but also their weaknesses when used in combination with other T-cell assays. Copyright © 2011 John Wiley & Sons, Ltd.

An oral recombinant Salmonella enterica serovar Typhimurium mutant elicits systemic antigen-specific CD8+ T cell cytokine responses in mice

Background

The induction of antigen-specific CD8+ T cell cytokine responses against an attenuated, oral recombinant Salmonella enterica serovar Typhimurium vaccine expressing a green fluorescent protein (GFP) model antigen was investigated. A GFP expression plasmid was constructed in which the gfp gene was fused in-frame with the 5' domain of the Escherichia coli β-galactosidase α-gene fragment with expression under the lac promoter. Groups of mice were orally immunized three times with the bacteria and systemic CD8+ T cell cytokine responses were evaluated.

Results

High level of the GFP model antigen was expressed by the recombinant Salmonella vaccine vector. Systemic GFP-specific CD8+ T cell cytokine (IFN-γ and IL-4) immune responses were detected after mice were orally vaccinated with the bacteria. It was shown that 226 net IFN-γ and 132 net IL-4 GFP-specific SFUs/10e6 splenocytes were formed in an ELISPOT assay. The level of IFN-γ produced by GFP peptide-stimulated cells was 65.2-fold above background (p < 0.05). The level of IL-4 produced by the cells was 10.4-fold above background (p < 0.05).

Conclusion

These results suggested that a high expressing recombinant Salmonella vaccine given orally to mice would elicit antigen-specific CD8+ T cell responses in the spleen. Salmonella bacteria may, therefore, be used as potential mucosal vaccine vectors.

Relationship between high-mobility group box 1 protein release and T-cell suppression in rats after thermal injury

To study whether high-mobility group box 1 protein (HMGB1) has an effect on T-cell-mediated immunity secondary to burn injury, 96 male Wistar rats weighing 250 to 300 g were randomly divided into three groups as follows:sham burn group, burn group, and burn with ethyl pyruvate treatment group, and they were killed on postburn days (PBDs)1, 3, 5, and 7, respectively, with 8 animals at each time point. Columns of nylon wool were used to isolate splenic T cells. T-Cell proliferation was analyzed with thiazolyl blue and expression of IL-2 receptor alpha (IL-2Ralpha) on the surface of T cell with flow cytometry. Levels of HMGB1 were determined using Western blot analysis. IL-2, soluble IL-2R, IL-4, and interferon-gamma were determined with enzyme-linked immunosorbent assay kits. Gene expressions of HMGB1, IL-2, and IL-2R were assessed using reverse-transcription polymerase chain reaction, and activation of nuclear factor of activated T cell was determined with gel mobility shift assay. The levels of HMGB1 in plasma were significantly elevated on PBDs 1 to 5. Significant proliferation of splenic T cells and IL-2, as well as IL-2Ralpha expression on T cells, were simultaneously suppressed to a certain extent on PBDs 1 to 7. Nuclear factor of activated T-cell activity of splenic T cells was markedly down-regulated on PBDs 1 to 3. Administration of ethyl pyruvate to inhibit HMGB1 can significantly restore proliferative activity, nuclear factor of activated T-cell activity, and expression levels of IL-2 and IL-2Ralpha on T cells. High-mobility group box 1 protein released after major burns might be associated with the pathogenesis of immunosuppression in splenic T lymphocytes in rats.

Single-dose, virus-vectored vaccine protection against Yersinia pestis challenge: CD4+ cells are required at the time of challenge for optimal protection

We have developed an experimental recombinant vesicular stomatitis virus (VSV) vectored plague vaccine expressing a secreted form of Yersinia pestis low calcium response protein V (LcrV) from the first position of the VSV genome. This vector, given intramuscularly in a single dose, induced high-level antibody titers to LcrV and gave 90-100% protection against pneumonic plague challenge in mice. This single-dose protection was significantly better than that generated by VSV expressing the non-secreted LcrV protein. Increased protection correlated with increased anti-LcrV antibody and a bias toward IgG2a and away from IgG1 isotypes. We also found that the depletion of CD4+ cells, but not CD8+ cells, at the time of challenge resulted in reduced vaccine protection, indicating a role for cellular immunity in protection.

IFN-gamma induces the erosion of preexisting CD8 T cell memory during infection with a heterologous intracellular bacterium

Memory T cells are critical for the control of intracellular pathogens and require few signals for maintenance; however, erosion of established preexisting memory CD8(+) T cells has been shown to occur during infection with heterologous viral infections. We evaluated whether this also occurs during infection with various intracellular bacteria and what mechanisms may be involved. We demonstrate that erosion of established memory is also induced during infection of mice with various intracellular bacteria, such as Listeria monocytogenes, Salmonella typhimurium, and Mycobacterium bovis (bacillus Calmette-Guérin). The extent of erosion of established CD8(+) T cell memory was dependent on the virulence of the heterologous pathogen, not persistence. Furthermore, when antibiotics were used to comprehensively eliminate the heterologous pathogen, the numbers of memory CD8(+) T cells were not restored, indicating that erosion of preexisting memory CD8(+) T cells was irreversible. Irrespective of the initial numbers of memory CD8(+) T cells, challenge with the heterologous pathogen resulted in a similar extent of erosion of memory CD8(+) T cells, suggesting that cellular competition was not responsible for erosion. After challenge with the heterologous pathogen, effector memory CD8(+) T cells were rapidly eliminated. More importantly, erosion of preexisting memory CD8(+) T cells was abrogated in the absence of IFN-gamma. These studies help reveal the paradoxical role of IFN-gamma. Although IFN-gamma promotes the control of intracellular bacterial replication during primary infection, this comes at the expense of erosion of preexisting memory CD8(+) T cells in the wake of infection with heterologous pathogens.

Mitogen activated protein kinase (MAPK) mediates non-genomic pathway of estrogen on T cell cytokine production following trauma-hemorrhage

Although studies have shown 17beta-estradiol (E2) administration following trauma-hemorrhage (T-H) attenuates alterations in T cell cytokine production, it remains unknown whether such effects of E2 are mediated via genomic or non-genomic pathways. In this study, we determined the non-genomic effects of E2 on splenic T cell cytokine production and the role of MAPK following T-H. Male Sprague-Dawley rats underwent T-H (mean BP 40 mmHg for 90 min, then resuscitation). E2, E2 conjugated with BSA (E2-BSA, 1 mg/kg E2) with or without an estrogen receptor antagonist (ICI 182 780), or vehicle was administered during resuscitation. Two hours thereafter, T cell production of IL-2 and IFN-gamma and activation of MAPK (p38, ERK-1/2 and JNK) were determined. The effect of selective MAPK inhibitors on cytokine production was also examined in vitro. IL-2 and IFN-gamma production capacity and MAPK activation decreased in T cells following T-H. However, E2 administration normalized these parameters. Although E2-BSA administration also attenuated suppression in cytokine production, the values were lower compared to sham. In contrast, E2-BSA prevented T-H-induced suppression in MAPK activation to the same extent as E2. Co-administration of ICI 182 780 abolished E2-BSA effects. These findings suggest E2 effects on T cell cytokine production following T-H are mediated at least in part via non-genomic pathway and these non-genomic effects are likely mediated via MAPK pathways.

HLA-A*0201-restricted cytotoxic T-cell epitopes in three PE/PPE family proteins of Mycobacterium tuberculosis

CD8+ T cells are thought to play an important role in protective immunity against tuberculosis. We report the identification of three peptides derived from Rv1818c, Rv3812 and Rv3018c proteins of Mycobacterium tuberculosis that bound to HLA-A*0201 molecules and their ability to induce in vitro T-cell response in peripheral blood lymphocytes from HLA-A*0201-positive healthy individuals (PPD+) and patients with TB. The peptide-specific cytotoxic T lymphocytes (CTL) generated were capable of recognizing peptide pulsed targets. Three 9-mer peptides bound with high affinity to HLA-A*0201 and displayed low dissociation rates of the bound peptide from HLA. Epitope-specific recognition was demonstrated by the release of perforin and gamma-interferon. Overall, our results demonstrate the presence of HLA class I-restricted CD8+ CTL against proteins from PE and PPE proteins of M. tuberculosis and identify epitopes that are strongly recognized by HLA-A*0201-restricted CD8+ T cells in humans. These epitopes thus represent potential subunit components for the design of vaccines against tuberculosis.

Salutary effects of 17beta-estradiol on T-cell signaling and cytokine production after trauma-hemorrhage are mediated primarily via estrogen receptor-alpha

Although 17beta-estradiol (E2) administration following trauma-hemorrhage prevents the suppression in splenocyte cytokine production, it remains unknown whether the salutary effects of 17beta-estradiol are mediated via estrogen receptor (ER)-alpha or ER-beta. Moreover, it is unknown which signaling pathways are involved in 17beta-estradiol's salutary effects. Utilizing an ER-alpha- or ER-beta-specific agonist, we examined the role of ER-alpha and ER-beta in E2-mediated restoration of T-cell cytokine production following trauma-hemorrhage. Moreover, since MAPK, NF-kappaB, and activator protein (AP)-1 are known to regulate T-cell cytokine production, we also examined the activation of MAPK, NF-kappaB, and AP-1. Male rats underwent trauma-hemorrhage (mean arterial pressure 40 mmHg for 90 min) and fluid resuscitation. ER-alpha agonist propyl pyrazole triol (PPT; 5 microg/kg), ER-beta agonist diarylpropionitrile (DPN; 5 microg/kg), 17beta-estradiol (50 microg/kg), or vehicle (10% DMSO) was injected subcutaneously during resuscitation. Twenty-four hours thereafter, splenic T cells were isolated, and their IL-2 and IFN-gamma production and MAPK, NF-kappaB, and AP-1 activation were measured. T-cell IL-2 and IFN-gamma production was decreased following trauma-hemorrhage, and this was accompanied with a decrease in T-cell MAPK, NF-kappaB, and AP-1 activation. PPT or 17beta-estradiol administration following trauma-hemorrhage normalized those parameters, while DPN administration had no effect. Since PPT, but not DPN, administration following trauma-hemorrhage was as effective as 17beta-estradiol in preventing the T-cell suppression, it appears that ER-alpha plays a predominant role in mediating the salutary effects of 17beta-estradiol on T cells following trauma-hemorrhage, and that such effects are likely mediated via normalization of MAPK, NF-kappaB, and AP-1 signaling pathways.

Characterization of early gamma interferon (IFN-gamma) expression during murine listeriosis: identification of NK1.1+ CD11c+ cells as the primary IFN-gamma-expressing cells

Though it is well established that gamma interferon (IFN-gamma) is crucial to the early innate defense of murine listeriosis, its sources remain controversial. In this study, intracellular cytokine staining of IFN-gamma-expressing splenocytes early after Listeria monocytogenes infection revealed that NK1.1(+), CD11c(+), CD8(+) T, and CD4(+) T cells expressed IFN-gamma 24 h after infection. Contrary to the previous report, most IFN-gamma(+) dendritic cells (DC) were CD8alpha(-) DC. Unexpectedly, almost all CD11c(+) IFN-gamma-expressing cells also expressed NK1.1. These NK1.1(+) CD11c(+) cells represented primary IFN-gamma-expressing cells after infection. In situ studies showed these NK1.1(+) CD11c(+) cells were recruited to the borders of infectious foci and expressed IFN-gamma. A significant NK1.1(+) CD11c(+) population was found in uninfected spleen, lymph node, blood, and bone marrow cells. And its number increased significantly in spleen, lymph node, and bone marrow after L. monocytogenes infection. Using interleukin-12 (IL-12) p40(-/-) mice, IFN-gamma expression was found to be largely IL-12 p40 dependent, and the number of IFN-gamma-expressing cells was only about one-third of that of wild-type mice. Moreover, the IFN-gamma expression was absolutely dependent on live L. monocytogenes infection, as no IFN-gamma was detected after inoculation of heat-killed L. monocytogenes. Our findings not only provide an insight into IFN-gamma expression after in vivo infection but may also change the current perceptions of DC and natural killer cells.

Gamma interferon, tumor necrosis factor alpha, and nitric oxide synthase 2, key elements of cellular immunity, perform critical protective functions during humoral defense against lethal pulmonary Yersinia pestis infection

Pulmonary infection by Yersinia pestis causes pneumonic plague, a rapidly progressing and often fatal disease. To aid the development of safe and effective pneumonic plague vaccines, we are deciphering mechanisms used by the immune system to protect against lethal pulmonary Y. pestis infection. In murine pneumonic plague models, passive transfer of convalescent-phase sera confers protection, as does active vaccination with live Y. pestis. Here, we demonstrate that protection by either protocol relies upon both gamma interferon (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) cytokines classically associated with type 1 cellular immunity. In both protocols, abrogating IFN-gamma or TNF-alpha activity significantly decreases survival and increases the bacterial burden in pulmonary, splenic, and hepatic tissues. Neutralization of either cytokine also counteracts challenge-induced, vaccination-dependent upregulation of nitric oxide synthase 2 (NOS2). Moreover, genetic depletion of NOS2 suppresses protection conferred by serotherapy. We conclude that IFN-gamma, TNF-alpha, and NOS2, key elements of cellular immunity, perform critical protective functions during humoral defense against lethal pulmonary Y. pestis challenge. These observations strongly suggest that plague vaccines should strive to maximally prime both cellular and humoral immunity.

Conversion of the severe to the moderate disease phenotype with donor leukocyte microchimerism in canine leukocyte adhesion deficiency

Leukocyte adhesion deficiency-1 (LAD-1), a genetic immunodeficiency disease characterized by life-threatening bacterial infections, results from the defective adherence and migration of leukocytes due to mutations in the leukocyte integrin CD18 molecule. Canine LAD (CLAD) represents the canine homologue of the severe phenotype of LAD-1 in children. In previous studies we demonstrated that non-myeloablative stem cell transplantation from matched littermates resulted in mixed donor-host chimerism and reversal of the disease phenotype in CLAD. In this study, we describe two CLAD dogs with less than 2% donor leukocyte chimerism following non-myeloablative transplant. Both dogs are alive more than 24 months after transplant with an attenuated CLAD phenotype resembling the moderate deficiency phenotype of LAD. The improvement in the CLAD phenotype with very low levels of donor CD18(+) leukocytes correlated with the preferential egress of the CD18(+) neutrophils into extravascular sites. The clinical response with very low levels of donor CD18(+) leukocytes in CLAD supports using this model for testing gene therapy strategies since the low levels of gene-corrected hematopoietic cells expected with hematopoietic gene therapy would likely have a therapeutic effect in CLAD.

Stimulation of CD8+ T cells following diphtheria toxin-mediated antigen delivery into dendritic cells

Recognition and clearance of many intracellular pathogens requires the activation and subsequent effector functions of CD8+ T lymphocytes. To stimulate CD8+ T cells by immunization, the target antigens must be delivered into the cytosol of host cells. There they can be processed into peptides and presented in the context of major histocompatibility complex class I molecules to antigen-specific CD8+ T cells. One method of delivering antigens into the cytosol is to fuse them to modified bacterial toxins that are able to enter mammalian cells. The expression pattern of the toxin receptors in the host will determine the cell population that the toxin fusion protein targets and will thus restrict antigen-specific T-cell recognition to the same population. In this study we describe the development and characterization of a diphtheria toxin (DT)-based antigen delivery system. Using CD11c-DTR transgenic mice that express the DT receptor in dendritic cells (DC), this system allows for targeted delivery of CD8+ T-cell antigen to DC. We show that antigen-specific CD8+ T cells proliferate in CD11c-DTR mice following immunization with catalytically inactive DT-antigen fusion proteins. We also show that a toxin-based system that restricts antigen delivery to DC results in more robust antigen-specific CD8+ T-cell proliferation than a toxin-based system that does not restrict delivery to a particular cell type. These results have implications for vaccine design, and they suggest that use of a toxin-based vector to target antigen to DC may be an effective way to induce a CD8+ T-cell response.

An update on the medical management of listeriosis

It is still not quite well understood why there is no optimal or even a satisfactory antibiotic therapy for listeriosis. Although almost all Listeria strains that induce sepsis, meningitis and encephalitis, as well as many other manifestations--in particular, in immunocompromised individuals--are susceptible to most of the common antibiotics, the cure rate is only approximately 70%. The most effective regimen still consists of a combination of an aminopenicillin (amoxicillin or ampicillin) plus an aminoglycoside. In vitro, this combination is bactericidal, whereas aminopenicillin alone only exerts a weak bactericidal activity against Listeriae. These antibiotics only poorly penetrate the cerebrospinal fluid and thus, only high doses given over a prolonged period of 2-3 weeks are curative. Furthermore, Listeria monocytogenes belongs to the group of facultative intracellular bacteria, which means that a certain population is inaccessible for antibiotics. Theoretically, a drug which is endowed with bactericidal activity superior to that of ampicillin would be preferable. Furthermore, the candidate drug should easily cross the blood-brain barrier into the CNS, be able to accumulate within host cells, reach the cytoplasm and be active under these unusual conditions. Because of all these arguments, the new quinolones are of particular interest; but broad clinical data are still lacking. It is unclear as to whether antibiotics alone will be sufficient to increase the prognosis. Adjunctive therapy with immunomodulators, which are able to reconstitute the defective defence capacities, would presumably create the conditions necessary to finally resolve listeriosis.

Corticosterone suppresses mesenteric lymph node T cells by inhibiting p38/ERK pathway and promotes bacterial translocation after alcohol and burn injury

Previous studies showed that alcohol (EtOH) intoxication before burn injury suppresses mesenteric lymph node (MLN) T cell functions and increases gut bacterial translocation. In this study, we examined whether corticosterone (Cort) plays any role in suppressing MLN T cell function and bacterial accumulation after EtOH intoxication and burn injury. Rats were gavaged with EtOH to achieve a blood EtOH level of approximately 100 mg/dl before receiving 25% total body surface area burn or sham injury. A group of rats was treated with the Cort synthesis inhibitor metyrapone (25 mg/kg) at the time of injury and on day 1 after injury. Two days after injury, a significant increase in blood Cort levels and suppression of MLN T cell proliferation and IL-2 production was observed in rats receiving combined insult of EtOH intoxication and burn injury compared with rats receiving EtOH intoxication or burn injury alone. There was no change in T cell apoptosis after combined insult of EtOH and burn injury. Furthermore, T cell suppression was accompanied by a significant decrease in p38 and ERK1/2 activation (phosphorylation). There was no difference in JNK activation after EtOH and burn injury. Treatment of rats with metyrapone prevented the suppression of MLN T cell proliferation, IL-2 production, and p38 and ERK1/2 phosphorylation. Restoration of T cell function in metyrapone-treated animals was also associated with the decrease in bacterial accumulation in MLN. These findings suggest that EtOH intoxication before burn injury augments Cort release, which suppresses MLN T cell function by inhibiting p38 and ERK1/2 activation and promotes bacterial accumulation in MLN after EtOH and burn injury.

Effect of acute alcohol ingestion prior to burn injury on intestinal bacterial growth and barrier function

Previous studies from our laboratory have shown that acute alcohol (EtOH) ingestion prior to burn injury enhances intestinal bacterial translocation. This study tested if increased intestinal bacterial translocation in alcohol and burn injured rats is due to an overgrowth in intestinal bacteria. We determined if the translocation was accompanied with alterations in intestinal permeability and immune cell population. Rats (225-250 g) were gavaged with alcohol to achieve a blood EtOH level in the range of 100 mg/dl prior to burn or sham injury (25% total body surface area). Two days after injury, we found that acute alcohol ingestions prior to burn injury results in a significant increase in bacterial counts in small intestine. The increase in intestinal bacterial counts accompanied a significant increase in intestinal permeability. Finally, immunohistochemical analysis revealed a substantial (p<0.05) loss of both T cell and dendritic cells in intestine of alcohol and burn injured rats compared with intestine of rats receiving either burn or sham injury. Altogether, results presented in this manuscript suggest that increase in intestinal bacterial growth along with alterations in intestinal permeability and immune status contribute to the increase in bacterial translocation observed in alcohol and burn injured rats.

Cloning and sequence analysis of llama cytokines related to cell-mediated immunity

In order to characterize the T helper 1 (Th1) cytokines of llama, we have cloned several llama cytokine genes and compared them to those of other mammalian species. The cDNAs encoding for interleukin (IL)-2, interferon (IFN), IL-12p35 and IL-12p40 were amplified using specific primers designed from reported sequences of bovine cytokine genes. The cDNAs for llama IL-2, IFN-, IL-12 p35 and IL-12p40 were found to be 465, 501, 669 or 993 bp in length, with open reading frames encoding 154, 166, 222 or 330 amino acids, respectively. Homology analyses of nucleotide and deduced amino sequences of llama IL-2, IFN-, IL-12p35 and IL-12p40 and phylogenetic analysis based on their nucleotide sequences indicated the close relationship in these cytokine genes between llama and eutherian mammalian order Artiodactyla, which includes pig and cattle.

Prolonged antigen presentation, APC-, and CD8+ T cell turnover during mycobacterial infection: comparison with Listeria monocytogenes

We expressed the CTL epitope of OVA (OVA(257-264)) in an acute (Listeria monocytogenes (LM)-OVA) and a chronic intracellular pathogen (Mycobacterium bovis (BCG)-OVA), to evaluate the kinetics of Ag presentation. LM-OVA proliferated rapidly in vivo, resulting in profound LM-OVA expansion within the first 24 h of infection, culminating in the generation of a potent CD8+ T cell response, which peaked on day 7 but underwent a rapid attrition subsequently. In contrast, BCG-OVA exhibited reduced growth in vivo, resulting in a delayed CD8+ T cell response that increased progressively with time. Relative to LM-OVA, BCG-OVA induced persistently increased numbers of apoptotic (annexin V+) CD8+ T cells. Ag presentation in vivo was evaluated by transferring Thy1.2+ carboxyfluorescein-labeled OT1 transgenic CD8+ T cells into infected Thy1.1+ congeneic recipient mice. LM-OVA induced rapid Ag presentation that was profound in magnitude, with most of the transferred cells getting activated within 4 days and resulting in a massive accumulation of activated donor CD8+ T cells. In contrast, Ag presentation induced by BCG-OVA was delayed, weaker in magnitude, which peaked around the second week of infection and declined to a low level subsequently. Increasing the dose of BCG-OVA while enhancing the magnitude of Ag presentation did not change the kinetics. Furthermore, a higher dose of BCG-OVA also accelerated the attrition of OVA(257-264)-specific CD8+ T cells. Relative to LM-OVA, the dendritic cells in BCG-OVA-infected mice were apoptotic for prolonged periods, suggesting that the rapid death of APCs may limit the magnitude of Ag presentation during chronic stages of mycobacterial infection.

Impaired intestinal immunity and barrier function: a cause for enhanced bacterial translocation in alcohol intoxication and burn injury

Alcohol intoxication is being recognized increasingly as the major factor in pathogenesis after burn injury. Findings from multiple studies support the suggestion that, in comparison with burn-injured patients who sustained injury in the absence of alcohol intoxication, burn-injured patients who sustained injury under the influence of alcohol exhibit higher rates of infection and are more likely to die. Thus, infection becomes the primary cause of death in burn-injured patients. Because the intestine is considered to be a major source of bacteria, studies in experimental animals have been designed to examine whether alcohol intoxication before burn injury enhances bacterial translocation from the intestine. Results of these studies have shown a several-fold increase in bacterial translocation from the intestine in the group of animals receiving combined insult of alcohol intoxication and burn injury compared with findings for the groups receiving either insult alone. Alcohol intoxication and burn injury independent of each other have also been shown to cause an increase in bacterial translocation. The gastrointestinal tract normally maintains a physical mucosal and immunologic barrier that provides an effective defense in keeping bacteria within the intestinal lumen. However, in injury conditions these defense mechanisms are impaired. Intestinal bacteria consequently gain access to extraintestinal sites. Intestine-derived bacteria are implicated in causing systemic infection and in subsequent multiple organ dysfunction in both immunocompromised patients and patients with injury, such as burn and trauma. In this article, we discuss three potential mechanisms that are likely to contribute to the increase in bacterial translocation in alcohol intoxication and burn injury: (1) increase in bacterial growth in the intestine, (2) physical disruption of mucosal barrier of the intestine, and (3) suppression of the immune defense in the intestine.

Analysis of autoreactive CD4 T cells in experimental autoimmune encephalomyelitis after primary and secondary challenge using MHC class II tetramers

Experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, is primarily mediated by CD4 T cells specific for Ags in the CNS. Using MHC class II tetramers, we assessed expansion and phenotypic differentiation of polyclonal self-reactive CD4 T cells during EAE after primary and secondary challenge with the specific Ag. After EAE induction in SJL mice with proteolipid protein 139-151, CNS-specific T cells up-regulated activation markers and expanded in the draining lymph nodes and in the spleen. Less than 20% of total autoreactive T cells entered the CNS simultaneously with Th cells of other specificities. Almost all tetramer-positive cells in the CNS were activated and phenotypically distinct from the large peripheral pool. When EAE was induced in Ag-experienced mice, disease symptoms developed earlier and persisted longer; autoreactive T cells were more rapidly activated and invaded the CNS earlier. In striking contrast to specific CTLs that respond after secondary viral challenge, the absolute numbers of autoreactive CD4 T cells were not increased, indicating that the accelerated autoreactivity in Ag-experienced mice is not related to higher frequencies of autoreactive CD4 T cells.

HLA-A2-restricted CD8+-cytotoxic-T-cell responses to novel epitopes in Mycobacterium tuberculosis superoxide dismutase, alanine dehydrogenase, and glutamine synthetase

Major histocompatibility complex class I-restricted CD8(+) cytotoxic T lymphocytes (CTL) are implicated in protective Th1 immunity to Mycobacterium tuberculosis infection. We report the identification of three novel HLA-A*0201-restricted CTL epitopes within mycobacterial superoxide dismutase (SodA), L-alanine dehydrogenase (AlaDH), and L-glutamine synthetase (GlnS) proteins.

Cloning and sequence analysis of llama cytokines related to cell-mediated immunity

In order to characterize the T helper 1 (Th1) cytokines of llama, we have cloned several llama cytokine genes and compared them to those of other mammalian species. The cDNAs encoding for interleukin (IL)-2, interferon (IFN)gamma, IL-12p35 and IL-12p40 were amplified using specific primers designed from reported sequences of bovine cytokine genes. The cDNAs for llama IL-2, IFN-gamma, IL-12 p35 and IL-12p40 were found to be 465, 501, 669 or 993 bp in length, with open reading frames encoding 154, 166, 222 or 330 amino acids, respectively. Homology analyses of nucleotide and deduced amino sequences of llama IL-2, IFN-gamma, IL-12p35 and IL-12p40 and phylogenetic analysis based on their nucleotide sequences indicated the close relationship in these cytokine genes between llama and eutherian mammalian order Artiodactyla, which includes pig and cattle.

A transgenic mouse model genetically tags all activated CD8 T cells

Identifying and characterizing Ag-specific CD8+ T cells are central to the study of immunological memory. Although powerful strategies such as MHC tetramers and peptide-induced cytokine production assays exist for identifying Ag-specific CD8+ T cells, alternate strategies that are not dependent upon a priori knowledge of the immunodominant and subdominant antigenic epitopes, as well as the MHC background of the animal are of obvious utility. In this study, we present a transgenic mouse model that uses Cre-loxP recombination to permanently mark all activated CD8+ T cells with beta-galactosidase. We used the lymphocytic choriomeningitis virus infection model to track the dynamics of the antiviral CD8+ T cell responses. We show that in this transgenic mouse model system, all of the antiviral effector and memory CD8+ T cells are contained within the beta-gal-marked CD8+ T cell population.

CD8 T cell responses to infectious pathogens

CD8 T cells respond to viral infections but also participate in defense against bacterial and protozoal infections. In the last few years, as new methods to accurately quantify and characterize pathogen-specific CD8 T cells have become available, our understanding of in vivo T cell responses has increased dramatically. Pathogen-specific T cells, once thought to be quite rare following infection, are now known to be present at very high frequencies, particularly in peripheral, nonlymphoid tissues. With the ability to visualize in vivo CD8 T cell responses has come the recognition that T cell expansion is programmed and, to a great extent, independent of antigen concentrations. Comparison of CD8 T cell responses to different pathogens also highlights the intricate relationship between microbially induced innate inflammatory responses and the kinetics, magnitude, and character of long-term T cell responses. This review describes recent progress in some of the major murine models of CD8 T cell-mediated immunity to viral, bacterial, and protozoal infection.

Attenuated Yersinia pseudotuberculosis carrier vaccine for simultaneous antigen-specific CD4 and CD8 T-cell induction

Yersinia pseudotuberculosis employs a type III secretion system for targeting of several virulence factors directly to the cytosol of eukaryotic cells. This protein translocation mechanism mediates the ability of Yersinia to resist phagocytosis and is required for sustained extracellular bacterial replication. In the present study, the Yersinia outer protein E (YopE) was used as a carrier molecule for type III-dependent secretion and translocation of listeriolysin O (LLO) from Listeria monocytogenes. In comparison to wild-type Yersinia, an attenuated Y. pseudotuberculosis yopK-null mutant strain hypertranslocates chimeric YopE/LLO into the cytosol of macrophages, resulting in enhanced major histocompatibility complex (MHC) class I-restricted antigen presentation of an LLO-derived CD8 T-cell epitope. Remarkably, T-cell activation assays also revealed a superior ability of translocated over secreted LLO to induce MHC class II-restricted antigen presentation. These in vitro observations were confirmed after immunization of mice with a single dose of the yopK-null mutant strain. Animals orally inoculated with recombinant Yersinia expressing translocated chimeric YopE/LLO revealed high numbers of gamma interferon-producing LLO-specific CD4 and CD8 T cells. For the first time, it is shown that cytosolic antigen display mediated by an extracellular bacterial carrier vaccine results in simultaneous CD4 and CD8 T-cell priming, conferring protection against an intracellular pathogen.

Advanced age negatively influences mesenteric lymph node T cell responses after burn injury

While the pathophysiology of burn injury is well established in young adults, the factors that contribute to pathogenesis and increased death in elderly burn patients are not defined. The purpose of this study is to determine the effects of burn injury on mesenteric lymph node (MLN) T cell responses in young and aged mice. MLN is a cluster of lymph nodes that drains various parts of the intestine and is known to play role in clearance bacteria originating from the intestinal lumen. Results presented here suggest a significant suppression in Con A-induced MLN cell proliferation and IL-2 production in uninjured aged mice compared with uninjured young mice. Following 24 h after injury, although, a significant decrease in lymph node cell proliferation and IL-2 production was observed in both young and aged mice compared with their respective sham-injured animals, the suppression was more in aged mice. In addition we found a reduction in IFN-gamma, a Th-1 cytokine by MLN T cells from aged burned mice relative to young burn (P<0.05) or sham-injured mice (P<0.01). The Th-2 cytokine IL-4, on the other hand, was significantly increased in both young and aged burn-injured mice MLN T cells compared with their respective sham-injured mice. These results show that burn injury causes a greater suppression in MLN T cells ability to proliferate and a more pronounced shift to Th-2 phenotype in aged mice as compared with young mice. Such decreases in T cell functions may impair MLN's ability to clear the bacterial pathogens originating from intestine and thereby contribute to increased pathogenesis in injured host.

CD8 T cell immunome analysis of Listeria monocytogenes

The identification of T cell epitopes is crucial for the understanding of the host response during infections with pathogenic microorganisms. Generally, the identification of relevant T cell responses is based on the analysis of T cell lines propagated in vitro. We used an ex vivo approach for the analysis of the CD8 T cell response against Listeria monocytogenes that is based upon the fractionation of naturally processed antigenic peptides and subsequent analysis with T cells in an enzyme-linked immunospot (ELISPOT) assay. Our data indicate that the direct ex vivo ELISPOT analysis of peptides extracted from infected tissues represents a versatile and potent test system for the analysis of the CD8 T cell immunome of microorganisms that furthermore requires neither the knowledge of the microbial genome nor of the specificity of responding T cells.

Prediction of spontaneous autoimmune diabetes in NOD mice by quantification of autoreactive T cells in peripheral blood

Autoimmune (type 1) diabetes mellitus results from the destruction of insulin-producing pancreatic beta cells by T lymphocytes. Prediction of cell-mediated autoimmune diseases by direct detection of autoreactive T cells in peripheral blood has proved elusive, in part because of their low frequency and reduced avidity for peptide MHC ligands. This article was published online in advance of the print edition. The date of publication is available from the JCI website, http://www.jci.org.

Prediction of spontaneous autoimmune diabetes in NOD mice by quantification of autoreactive T cells in peripheral blood

Autoimmune (type 1) diabetes mellitus results from the destruction of insulin-producing pancreatic beta cells by T lymphocytes. Prediction of cell-mediated autoimmune diseases by direct detection of autoreactive T cells in peripheral blood has proved elusive, in part because of their low frequency and reduced avidity for peptide MHC ligands. This article was published online in advance of the print edition. The date of publication is available from the JCI website, http://www.jci.org.

The innate immune response against Brucella in humans

Pathogens have developed different strategies to survive and multiply within their host. Among them is the ability to control phagocyte apoptosis while another is to affect the expression of cytokines which is necessary for a normal protective function of the immune response. To establish themselves and cause chronic disease in humans and animals, Brucella spp. invade and proliferate within monocytic phagocytes. We have established that in humans, Brucella suis impairs the apoptosis of monocytes and macrophages, thus preventing its host cell elimination. In mice, which are not naturally colonized by the bacteria, Brucella infection results in Type1 (Th1) cellular immune response which promotes a clearance of the bacterial organism. The development of this response is under the control of major cytokines like TNF-alpha, IFN-gamma and IL-12 produced at the onset of infection. We have observed that in humans, B. suis-infected macrophages which produce IL-1, IL-6, IL-10 and several chemokines including IL-8, do not secrete TNF-alpha. By constructing null mutants, we demonstrated that this inhibition involves the outer membrane protein Omp25 of Brucella, however the mechanism regulating the inhibition has not yet been clearly defined. It is likely that the Omp25-induced effect on TNF-alpha production assists bacterial evasion of antimicrobial defences at different levels. Firstly, by preventing the autocrine activation of macrophages thus inhibiting innate immunity and secondly by impairing the production of IL-12 and the development of a Th1 type specific immunity. In addition to the central role of the macrophage in Brucella infection, others cells of the innate immune response are recruited and influenced by the interactions between bacteria and host. For instance, human Vgamma9Vdelta2 T-cells play an important role in the early response to infection with intracellular pathogens. Evidence has been presented that their number dramatically increased in the peripheral blood of patients with acute brucellosis. We have shown that human Vgamma9Vdelta2 T-cells can be specifically activated by non-peptidic low molecular weight compound(s) from B. suis lysate or by soluble factors produced by B. suis-infected macrophages. Under these conditions, they produce TNF-alpha and IFN-gamma and reduce the bacterial multiplication inside infected autologous macrophages. This impairment of B. suis multiplication is due to both soluble factors released from activated gammadeltaT-cells (including TNF-alpha and IFN-gamma) and to a contact-dependent cytotoxicity directed against the infected cells. The interactions between the bacteria and these cells can counteract the intramacrophagic development of the bacteria and finally influence the further development of the host defense. We hypothesize that the chronicity or the elimination of the infection will depend on the balance between contradictory effects induced by the bacteria which favor either the host or the pathogen. Moreover, the interrelationship between the different cells must be taken into account in the analysis of the virulence of the bacteria and in the development of in vitro models of human macrophage infection.

Minimal contribution of Valpha14 natural killer T cells to Th1 response and host resistance against mycobacterial infection in mice

We elucidated the contribution of Valpha14 NKT cells to Th1 response and host resistance against mycobacterial infection. In Valpha14 NKT cell-deficient mice, host defense and DTH response to Mycobacterium bovis BCG were not different from wild-type mice after pulmonary infection. There was no significant difference in the lung concentrations of IFN-gamma between the two strains of mice. In addition, host defense to systemic infection with M. tuberculosis was similar to that of M. bovis. Our results indicate that Valpha14 NKT cells play only a marginal role, if any, in the Th1 response and host resistance to mycobacterial infection.

Adjuvant regulation of cytokine profile and antibody isotype of immune responses to Mycoplasma agalactiae in mice

Traditionally, adjuvants have been administered with antigens to enhance immunity. We studied the effect of several adjuvants such as Freund's complete adjuvant (FCA), Freund's incomplete adjuvant (FIA), lipopolysaccharide (LPS), homopolymers of polyinosinic-polycytidylic acid (poly I:C) and polyadenylic-polyuridylic acid (poly A:U), lithium chloride (LiCl), saponin Quil A and calcium phosphate gel (CaHPO(4)) on the immune response of mice to formalin-inactivated Mycoplasma agalactiae. The specific antibody or cytokine producing splenocytes were detected by ELISAspot and immunocytochemistry, respectively. Depending on the adjuvant given, the number of M. agalactiae-specific antibody producing cells was increased 2.5-6-fold. IgG was the major class of M. agalactiae-specific antibodies followed by IgM, IgA and IgE. Among IgG isotypes, FCA, FIA, Quil A and CaHPO(4) induced an IgG1 response with substantial increase of the IgG2a, IgG2b and IgG3 isotypes while poly I:C shifted the response toward an IgG2a/IgG3 production. Finally, poly A:U induced an IgG2b response while LPS and LiCl augmented the IgG3/IgG1/IgG2a secretion. FCA augmented IL-4, IL-5 and IL-10 production suggesting a strong Th2 response, while IFN-gamma and IL-12 remained low; poly I:C enhanced IFN-gamma, IL-12 and TNF-alpha eliciting a Th1 response; poly A:U resulted in a IL-10, IL-5, IL-6 and IL-12 secretion; and LPS enhanced the IL-10, IL-6 and TNF-alpha production. Our data show that adjuvants augment M. agalactiae-specific antibody production and lead to B cell isotype-switching via the appropriate cytokine milieu. Certain adjuvants, such as poly I:C, therefore, appear as promising immune enhancers for vaccination against M. agalactiae infections.

Role of NFAT and AP-1 in PGE2-mediated T cell suppression in burn injury

PGE2 is known to suppress T cell proliferation and IL-2 production in many inflammatory conditions. Previous studies from our laboratory have shown that such suppression of T cell proliferation in burn and sepsis could result from alteration in T cell activation signaling molecule p59fyn. In this study, we examined the role of downstream signaling molecules NFAT and AP-1 in PGE2-mediated suppression of T cell in burn injury. These studies were carried out utilizing splenic T cells from sham and burn rats 3 days after injury. The data presented in this manuscript suggest a significant suppression of IL-2 production by T cells from burn injured rats compared with the T cells from sham rats. The suppression in T cell IL-2 production was accompanied by a decrease in the activation of NFAT and AP-1 as well as a decrease in T cell p59fyn kinase activity. The treatments of burn-injured animals with PGE2 synthesis blocker indomethacin prevented both the decrease in NFAT and AP-1 binding to IL-2 sequences. In vitro incubation of control rat T cells with PGE2 suppressed the activation of NFAT and AP-1. These results suggested that the suppression of T cell IL-2 production could result from PGE2-mediated alterations in the T cell signaling molecule p59fyn and NFAT/AP-1.

Cross-reactive antigen is required to prevent erosion of established T cell memory and tumor immunity: a heterologous bacterial model of attrition

Induction and maintenance of T cell memory is critical for the control of intracellular pathogens and tumors. Memory T cells seem to require few "maintenance signals," though often such studies are done in the absence of competing immune challenges. Conversely, although attrition of CD8(+) T cell memory has been characterized in heterologous viral models, this is not the case for bacterial infections. In this study, we demonstrate attrition of T cell responses to the intracellular pathogen Listeria monocytogenes (LM) following an immune challenge with a second intracellular bacterium, Mycobacterium bovis (bacillus Calmette-Guérin, BCG). Mice immunized with either LM or recombinant LM (expressing OVA; LM-OVA), develop a potent T cell memory response. This is reflected by peptide-specific CTL, IFN-gamma production, and frequency of IFN-gamma-secreting T cells to native or recombinant LM Ags. However, when the LM-infected mice are subsequently challenged with BCG, there is a marked reduction in the LM-specific T cell responses. These reductions are directly attributable to the effects on CD4(+) and CD8(+) T cells and the data are consistent with a loss of LM-specific T cells, not anergy. Attrition of the Ag (OVA)-specific T cell response is prevented when LM-OVA-immunized mice are challenged with a subsequent heterologous pathogen (BCG) expressing OVA, demonstrating memory T cell dependence on Ag. Although the reduction of the LM-specific T cell response did not impair protection against a subsequent LM rechallenge, for the first time, we show that T cell attrition can result in the reduction of Ag-specific antitumor (B16-OVA) immunity previously established with LM-OVA immunization.

Cross-presentation of Listeria monocytogenes-derived CD4 T cell epitopes

Listeriolysin O (LLO) mediates the evasion of Listeria monocytogenes from the phagolysosome into the cytoplasm of the host cell. The recognition of infected cells by CD4 T cells is thought to be limited by the evasion of bacteria from the phagolysosome and also by the direct LLO-mediated inhibition of CD4 T cell activation. To analyze the influence of these immunoevasive mechanisms on the antilisterial CD4 T cell response, the expansion of L. monocytogenes-specific CD4 and CD8 T cells was monitored in infected mice. It was found that expansion of L. monocytogenes-specific CD4 T cells occurred synchronously with CD8 T cell expansion. The analysis of Ag presentation by macrophages and dendritic cells isolated from spleens of infected mice revealed efficient presentation of L. monocytogenes-derived CD4 T cell epitopes that was not dependent on the actA-mediated intercellular spread of bacteria. The further in vitro Ag presentation analysis revealed that although L. monocytogenes-infected macrophages and dendritic cells were poor presenters of CD4 T cell epitopes, more efficient presentation occurred after cocultivation of noninfected dendritic cells or macrophages with infected cells. These data indicate that the suppressive effect of LLO on the antilisterial CD4 T cell response is maintained only in infected APC and support the hypothesis that cross-priming plays a role in the induction of the strong CD4 T cell response in Listeria-infected mice.

Detection and analysis of antigen-specific CD8+ T cells

Based on recent advances in techniques that can detect and enumerate antigen-specific CD8+ T cells, it is evident that these cells can differentially regulate CD8+ T cell effector mechanisms at the single-cell level. Interplay between effector mechanisms that are employed by antigen-specific CD8+ T cells during the immune response in vivo can be addressed with different techniques that "count" cells either directly (T cell receptor (TCR) expression) or indirectly (antigen-specific cytokine production).

Multiple mechanisms compensate to enhance tumor-protective CD8(+) T cell response in the long-term despite poor CD8(+) T cell priming initially: comparison between an acute versus a chronic intracellular bacterium expressing a model antigen

We evaluated CD8(+) T cell responses against the dominant CTL epitope, OVA(257-264), expressed by an acute (Listeria monocytogenes (LM) OVA) vs a chronic pathogen (Mycobacterium bovis bacillus Calmette-Guérin (BCG) OVA) to reveal the influence on CD8(+) T cell memory and consequent protection against a challenge with OVA-expressing tumor cells. Infection with lower doses of both pathogens resulted in stronger bacterial growth but weaker T cell memory indicating that memory correlates with pathogen dose but not with bacterial expansion. The CD8(+) T cell response induced by LM-OVA was helper T cell-independent and was characterized by a rapid effector response followed by a rapid, but massive, attrition. In contrast, BCG-OVA induced a delayed and weak response that was compensated for by a longer effector phase and reduced attrition. This response was partly dependent on CD4(+) T cells. CD8(+) T cell response induced by BCG-OVA, but not LM-OVA, was highly dependent on pathogen persistence to compensate for the weak initial CD8(+) T cell priming. Despite a stronger initial T cell response with LM-OVA, BCG-OVA provided more effective tumor (B16OVA) control at both local and distal sites due to the induction of a persistently activated acquired, and a more potent innate, immunity.

Gut-associated lymphoid T cell suppression enhances bacterial translocation in alcohol and burn injury

The mechanism of alcohol-mediated increased infection in burn patients remains unknown. With the use of a rat model of acute alcohol and burn injury, the present study ascertained whether acute alcohol exposure before thermal injury enhances gut bacterial translocation. On day 2 postinjury, we found a severalfold increase in gut bacterial translocation in rats receiving both alcohol and burn injury compared with the animals receiving either injury alone. Whereas there were no demonstrable changes in intestinal morphology in any group of animals, a significant increase in intestinal permeability was observed in ethanol- and burn-injured rats compared with the rats receiving either injury alone. We further examined the role of intestinal immune defense by determining the gut-associated lymphoid (Peyer's patches and mesenteric lymph nodes) T cell effector responses 2 days after alcohol and burn injury. Although there was a decrease in the proliferation and interferon-gamma by gut lymphoid T cells after burn injury alone; the suppression was maximum in the group of rats receiving both alcohol and burn injuries. Furthermore, the depletion of CD3(+) cells in healthy rats resulted in bacterial accumulation in mesenteric lymph nodes; such CD3(+) cell depletion in alcohol- and burn-injured rats furthered the spread of bacteria to spleen and circulation. In conclusion, our data suggest that the increased intestinal permeability and a suppression of intestinal immune defense in rats receiving alcohol and burn injury may cause an increase in bacterial translocation and their spread to extraintestinal sites.