Cytotoxic T cell responses to intracellular pathogens

The Human Immune System toward Staphylococcus aureus

The immune system is responsible for protecting the host from pathogens, and it has evolved to deal with these pathogens. On the other hand, the co-evolution of pathogenic bacteria with hosts has led to the rise of an array of virulence genes that enable pathogen bacteria to evade or modulate the immune system. Staphylococcus aureus is a significant pathogen of humans that encodes several virulence factors that can modulate or evade from the innate and adaptive arm of the immune system. Overall, the immune reaction toward S. aureus contributes to stimulate innate and adaptive reactions. A profound understanding of the immune response to S. aureus infections will be critical for the development of vaccines and novel therapies. In this review, we summarized and discussed the novel information about the human immune system against S. aureus.

Catfish lymphocytes expressing CC41-reactive leukocyte immune-type receptors (LITRs) proliferate in response to Edwardsiella ictaluri infection in vitro

Monoclonal antibodies (mAbs) CC34 and CC41 recognize overlapping subsets of leukocyte immune-type receptors (LITRs). The mAb CC34 was raised against the clonal TS32.15 cytotoxic T cell line and the mAb CC41 was raised against the clonal NK cell line TS10.1. In this study, an in vitro model was developed to monitor CC34- and CC41-reactive cells in response to Edwardsiella ictaluri infection. Briefly, head kidney leukocytes and peripheral blood lymphocytes (PBL) were isolated from individual catfish and labeled with CellTrace Violet and CellTrace FarRed dye, respectively. Head kidney-derived macrophages were infected with E. ictaluri and then cocultured with autologous PBL. The combined cell cultures were then analyzed using flow cytometry. A significant increase in CC41 staining was observed in the PBL population at 2, 5 and 7 days after culture, which suggest that LITRs are involved in cell-mediated immunity to E. ictaluri.

Activated cytotoxic T cells within zoonotic cutaneous leishmaniasis lesions

Introduction

Zoonotic cutaneous leishmaniasis (ZCL), due to infection by Leishmania (L). major, is characterized by polymorphic clinical manifestations which could be attributed to the host's immune response. In this study we investigated the involvement of cytotoxic cells on the outcome of the disease.

Methods

Expression of granzyme B (GrB), granulysine (Grly), and interferon (IFN)‐γ was evaluated within ZCL lesion specimens using the technique of real‐time quantitative polymerase chain reaction (RT‐qPCR). Immunohistochemical staining was performed using anti‐CD3, CD4, CD8, CD56, GrB, and IFN‐γ antibodies to identify the phenotype of GrB and IFN‐γ‐producing cells.

Results

GrB and Grly mRNA was detected within 75% and 80% of ZCL lesions, respectively. Statistical analysis demonstrated a significant correlation between levels of GrB and Grly. Interestingly, expression of these molecules correlates negatively with the lesion's age. The highest levels were measured in early lesions (E‐ZCL) (lesion age ≤1 month) comparing to late lesions (L‐ZCL) (lesion age >1 month). Otherwise, IFN‐γ mRNA was detected only within 56% and a positive correlation was found between levels of this cytokine and those of GrB. Immunohistochemical analysis showed that GrB is produced essentially by CD8⁺T cells whereas IFN‐γ is produced by both CD4⁺ and CD8⁺T cells.

Conclusion

Together our results demonstrate the presence of cytotoxic cells producing GrB and Grly within leishmaniasis cutaneous lesions.

Efficacy of a potential DNA vaccine encoding Cryptosporidium baileyi rhomboid protein against homologous challenge in chickens

The parasite Cryptosporidium baileyi can infect the larynx, trachea, bursa and cloaca of poultry, causing high mortality during severe infection and leading to substantial economic losses of the poultry industry. The rhomboid protein is very important in Cryptosporidium infection. In this study, a nucleic acid based vaccine candidate pEGFP-CbROM was constructed. After orally challenging with C. baileyi oocysts, the corresponding immune responses induced were analyzed and the immunoprotective effect evaluated in chickens. Obtained results revealed that this nucleic acid based vaccine could induce antibody responses and peripheral blood T lymphocytes proliferation significantly (P<0.05), while the peripheral blood B lymphocyte proliferation increased significantly (P<0.05) only at a high dose of 100μg of pEGFP-CbROM, compared with the PBS control group. After C. baileyi infection, the duration of oocysts shedding was shortened by 2days in the 100μg pEGFP-CbROM group, and the rate of reduction could reach to around 71.3%. While no significant difference in body weight gain was observed among the immunized groups (P>0.05), the differences between the immunized and the non-immunized groups were found to be significant (P<0.05). Our data provides a useful basis for further work in cryptosporidiosis prevention and treatment.

Potential diagnostic value of serum/pleural fluid IL-31 levels for tuberculous pleural effusion

The aim of this study was to explore the diagnostic value of IL-31 levels in the pleural fluid and plasma to differentially diagnose tuberculous and malignant pleural effusion. We enrolled 91 cases, including tuberculous pleural effusion (TPE, n = 50), malignant pleural effusion (MPE, n = 41), other cases including pneumonia with pleural fluid, pulmonary tuberculosis and healthy people as controls. Whole blood was stimulated with the M. tuberculosis-specific antigens and plasma was collected. The multiplex bead-based cytokine immunoassay was employed to measure the levels of various cytokines. IL-31 was found to be the most prominent cytokine (P < 0.0001), and with an optimal cut-off value of 67.5 pg/mL, the sensitivity and specificity for the diagnosis of TPE were 86% and 100%, respectively. Furthermore, the tuberculosis-specific IL-31 levels in the plasma of TPE patients were higher than that of MPE patients (P = 0.0002). At an optimal cut-off value of 23.9 pg/mL, the sensitivity and specificity for the diagnosis of TPE were 92.9% and 85.7%, respectively. Ultimately, the combination of pleural fluid with the plasma tuberculosis-specific IL-31 levels improved the sensitivity and specificity to 94.0% and 95.1%, respectively. Thus, we identified a novel biomarker for the diagnosis of TPE for clinical application.

Characterization of CD4/CD8+ αβ and Vγ2Vδ2+ T cells in HIV-negative individuals with different Mycobacterium tuberculosis infection statuses

BACKGROUND

The immune responses of T cell subsets among patients with different Mycobacterium tuberculosis (M.tb) infection statuses [i.e., active tuberculosis (ATB), latent tuberculosis infection (LTBI) and non-infection (healthy control, HC)] have not been fully elucidated in HIV-negative individuals. Specifically, data are limiting in high tuberculosis epidemic regions in China. To investigate the distributions and functions of T cell subsets (i.e., CD3+, CD4+, CD8+ αβ and Vγ2Vδ2+ T cells) in HIV-negative subjects with different M.tb infection statuses, we conducted a case-control study that enrolled 125 participants, including ATB patients (n = 46), LTBI subjects (n = 34), and HC (n = 45).

RESULTS

An IFN-γ release assay (IGRA) was employed to screen LTBI subjects. Whole blood cell surface staining and flow cytometry were used to detect phenotypic distributions of T cells in the peripheral blood mononuclear cells (PBMCs) and tuberculous pleural fluid mononuclear cells (PFMCs). PPD and the phosphorylated antigen HMBPP were employed as stimulators for the detection of M.tb antigen-specific T cell functions via intracellular cytokine staining (ICS). The absolute numbers of T cell subsets, including CD3+ CD4+, CD3+ CD8+ αβ and Vγ2Vδ2+ T cells, were significantly reduced in active tuberculosis compared with latent tuberculosis or the healthy controls. Importantly, PPD-specific CD3+ CD4+ and CD3+ CD8+ αβ T cells and HMBPP-specific Vγ2Vδ2+ T cells in ATB patients were also significantly reduced compared to the LTBI/HC subjects (P<0.05). In contrast, the proportion of CD4+ T cells in PFMCs was higher compared to PBMCs, while CD8+ and Vγ2Vδ2+ T cells in PFMCs were lower compared to PBMCs (all P < 0.05). PPD-specific CD4+ T cells predominated among CD3+ T cells in PFMCs.

CONCLUSIONS

Cellular immune responses are impaired in ATB patients. Antigen-specific CD4+ T cell may migrate from the periphery to the lesion site, where they exert anti-tuberculosis functions.

Cytokine-like molecule CCDC134 contributes to CD8⁺ T-cell effector functions in cancer immunotherapy

CCDC134 is a poorly characterized secreted protein that may act as an immune cytokine. Here, we show that CCDC134 is differentially expressed on resting and activated immune cells and that it promotes CD8(+) T-cell activation, proliferation, and cytotoxicity by augmenting expression of the T-cell effector molecules IFNγ, TNFα, granzyme B, and perforin. CCDC134 facilitated infiltration of CD8(+) T cells with enhanced cytolytic activity into tumors, demonstrating strong antitumor effects in a CD8(+) T-cell-dependent manner. Mechanistically, in CD8(+) T cells, exposure to CCDC134 promoted cell proliferation through the JAK3-STAT5 pathway, a classic feature of many cytokines of the common γ-chain (γ(c)) cytokine receptor family. Overall, our results provide evidence that CCDC134 may serve as a member of the γ(c) cytokine family and illustrate its potent antitumor effects by augmenting CD8(+) T-cell-mediated immunity.

Intracellular immunity: finding the enemy within--how cells recognize and respond to intracellular pathogens

Historically, once a cell became infected, it was considered to be beyond all help. By this stage, the invading pathogen had breached the innate defenses and was beyond the reach of the humoral arm of the adaptive immune response. The pathogen could still be removed by cell-mediated immunity (e.g., by NK cells or cytotoxic T lymphocytes), but these mechanisms necessitated the destruction of the infected cell. However, in recent years, it has become increasingly clear that many cells possess sensor and effector mechanisms for dealing with intracellular pathogens. Most of these mechanisms are not restricted to professional immune cells nor do they all necessitate the destruction of the host. In this review, we examine the strategies that cells use to detect and destroy pathogens once the cell membrane has been penetrated.

Abelson tyrosine kinase controls phagosomal acidification required for killing of Mycobacterium tuberculosis in human macrophages

The mechanisms that regulate the acidification of intracellular compartments are key to host defense against pathogens. In this paper, we demonstrate that Abl tyrosine kinase, a master switch for cell growth and trafficking of intracellular organelles, controls the acidification of lysosomes in human macrophages. Pharmacological inhibition by imatinib and gene silencing of Abelson (Abl) tyrosine kinase reduced the lysosomal pH in human macrophages by increasing the transcription and expression of the proton pumping enzyme vacuolar-type H(+)-adenosine triphosphatase. Because lysosomal acidification is required for antimicrobial activity against intracellular bacteria, we determined the effect of imatinib on the growth of the major human pathogen Mycobacterium tuberculosis. Imatinib limited the multiplication of M. tuberculosis, and growth restriction was dependent on acidification of the mycobacterial compartment. The effects of imatinib were also active in vivo because circulating monocytes from imatinib-treated leukemia patients were more acidic than monocytes from control donors. Importantly, sera from imatinib-treated patients triggered acidification and growth restriction of M. tuberculosis in macrophages. In summary, our results identify the control of phagosomal acidification as a novel function of Abl tyrosine kinase and provide evidence that the regulation occurs on the level of the vacuolar-type H(+)-adenosine triphosphatase. Given the efficacy of imatinib in a mouse model of tuberculosis and our finding that orally administered imatinib increased the ability of human serum to trigger growth reduction of intracellular M. tuberculosis, clinical evaluation of imatinib as a complementary therapy of tuberculosis, in particular multidrug or extremely drug-resistant disease, is warranted.

Lymphocyte phenotyping, using cluster-of-differentiation (CD) markers, in young Iraqi children with visceral leishmaniasis

The lymphocytic phenotypes involved in the pathogenesis of visceral leishmaniasis (VL) in Iraqi children have recently been investigated, in a study based on cluster-of-differentiation (CD) markers. Each case of VL investigated was confirmed parasitologically by the observation of amastigotes in a bone-marrow smear. Compared with the values for the healthy children used as controls, a lymphocyte from an untreated VL case was significantly less likely to be CD3+ or CD4+, significantly more likely to be CD8+, and more (but not significantly more) likely to be CD22+. The untreated cases also had significantly lower CD4+/CD8+ ratios than the controls. Among the untreated cases, gender and age had no apparent effect on any of these variables. After 28 days of treatment with sodium stibogluconate, there was a trend towards normalization in the lymphocytic phenotypes of the VL cases, with significant increases in the CD4+/CD8+ ratios and the percentages of lymphocytes that were CD3+ or CD4+, and a significant decrease in the percentages of lymphocytes that were CD22+.

Immunohistochemical analysis of cytokines and apoptosis in tuberculous lymphadenitis

Relatively little is known about the effector mechanisms whereby the human immune system controls Mycobacterium tuberculosis infection. In this study we elaborate on the immune response and mechanisms of persistence of mycobacteria in lesions by analysing, using immunohistochemistry, the expression of cytokines [tumour necrosis factor-alpha (TNF-alpha), interleukin-10 (IL-10), transforming growth factor-beta (TGF-beta) and interferon-gamma (IFN-gamma)], apoptotic cells and apoptosis-related proteins [Bcl2, Bax, Fas ligand (FasL) and Fas] in the human tuberculous lymphadenitis lesions. The expression of apoptosis-related proteins has been shown to be exploited by mycobacteria to evade the immune response and persist in the host. Foreign body (FB) granulomas were used as controls. In tuberculosis (TB) granulomas, epithelioid cells and multinucleated giant cells expressed cytokines differently. In epithelioid cells, the numbers of TNF-alpha-, IL-10- and TGF-beta-stained cells were higher than IFN-gamma-stained cells (P < 0.01). TGF-beta and FasL were strongly expressed in the necrotic centres as compared with other cytokines. More giant cells expressed IL-10 and TGF-beta than expressed TNF-alpha and IFN-gamma (P < 0.01). Staining of consecutive sections revealed that some giant cells expressed IL-10 but not TNF-alpha. Apoptotic TB giant cells correlated positively with the expression of TNF-alpha, IFN-gamma and TGF-beta, but not with the expression of IL-10. The percentage of giant cells expressing Bax was lower than those expressing Fas, unlike the epithelioid cells, suggesting that TB giant cells are less susceptible to apoptosis. Compared with FB giant cells, there were fewer TB giant cells showing TNF-alpha, IFN-gamma, FasL, Fas expression or undergoing apoptosis (P < 0.05). Taken together, these observations show that the cellular microenvironment of TB granulomas down-regulates microbicidal functions, favouring bacillary survival and persistence. TGF-beta and FasL may be responsible for tissue destruction. The giant cells, being less susceptible to apoptosis, may remain a continuous source of pro-inflammatory cytokines, causing immune pathology.

Specific Alteration of Peripheral Cytotoxic Cell Perforin Expression in Alcoholic Patients: A Possible Role in Alcohol-Related Diseases

BACKGROUND

The association between chronic alcohol consumption and an increasing risk of infectious and neoplastic disease is related to an impairment of cellular immunity. However, studies of the number and activity of lymphocyte subsets show highly variable results. The aim of this study was to assess the expression of perforin, one of the main molecular agents of T and natural killer (NK) cell-mediated cytotoxicity, in alcoholic patients without cirrhosis.

METHODS

Eighteen patients with chronic alcoholism were prospectively included and compared with 18 age- and sex-matched healthy volunteers. Signs of hepatic insufficiency or portal hypertension, viral co-infection, other serious medical illness, and immune-related medications were exclusion criteria. Lymphocyte phenotype was assessed, and perforin expression was analyzed by flow cytometry in CD3+CD56+ T cells and NK cells. Granzyme synthesis was also evaluated in 11 of the 18 patients and compared with that of 11 age- and sex-matched controls.

RESULTS

The mean number of white blood cells and lymphocytes was not different between the controls and alcoholic patients, whereas the mean number of NK cells was significantly decreased in alcoholic patients (110 +/- 79/mm3 versus 271 +/- 192/mm3; p < 0.03). Perforin expression in T CD3+/CD56+ and in NK cells was significantly decreased in alcoholic patients compared with controls: 16 +/- 3% vs. 36 +/- 4% (p < 0.03) and 65 +/- 15% vs. 78 +/- 9% (p = 0.04), respectively. The percentage of cells expressing granzyme was similar in both groups.

CONCLUSIONS

A decrease in perforin expression by cytotoxic cells could be a major factor in explaining the physiopathologic mechanisms of several alcohol-associated diseases.

Characteristics of immune response to protozoan infections

Introduction When protozoa enter the blood stream or tissues they can often survive and replicate because they adapt to the resisting natural host defenses. The interaction of immune system with infectious organisms is a dynamic interplay of host mechanisms aimed at eliminating infections and microbial strategies designed to permit survival in the face of powerful effectors mechanisms. Protozoa cause chronic and persistent infections, because natural immunity against them is weak and because protozoa have evolved multiple mechanisms for evading and resisting specific immunity. Natural and specific immune response to protozoa Different protozoa vary greatly in their structural and biochemical properties and stimulate distinct patterns of immune responses and have evolved unique mechanisms for evading specific immunity. Protozoa activate quite distinct specific immune responses, which are different from the responses to fungi, bacteria and viruses. Protozoa may be phagocytozed by macrophages, but many are resistant to phagocytic killing and may even replicate within macrophages. T. brucei gambiense is the best example of protozoa which can induce humoral immune response because of its extra-cellular location. In Leishmania sp. infections, cellular defense mechanisms depend upon CD4+ T-lymphocytes and activate macrophages as effectors cells that are regulated by cytokines of Th1 subset. Plasmodium sp. is a protozoa which show the diversity of defence mechanisms which can be cellular or humoral, depending on Ag and protozoa's location. Immune evasion mechanisms of protozoa Different protozoa have developed remarkably effective ways of resisting specific immunity: a) anatomic sequestration is commonly observed with protozoa Plasmodium and T. gondii; b) some protozoa can become resistant to immune effectors mechanisms: Trypanosoma, Leishmania and T. gondii; c) some protozoa have developed effective mechanisms for varying their surface antigens: Plasmodium and Trypanosoma; d) some protozoa shed their antigen coats, either spontaneously or after binding with specific antibodies: E. histolytica; e) some protozoa alter host immune response by nonspecific and generalized immunosuppression (abnormalities in cytokine production, deficient T cell activation): Trypanosoma, Leishmania, Toxoplasma, Entamoeba. Conclusion Protozoa activate numerous, different immune mechanisms in human body. Evolution, progression and outcome of diseases depend upon these mechanisms. Resent progresses in research have defined and selected Ag as candidates for new vaccines. Better definitions regarding the role of cytokines in protozoaninfections will facilitate rational development of cytokines and cytokine antagonists and their use as immunotherapeutic agents.

Macrophage activation syndrome

Macrophage activation syndrome (MAS) is a serious complication of childhood systemic inflammatory disorders that is thought to be caused by excessive activation and proliferation of T lymphocytes and macrophages. Recent findings in hemophagocytic lymphohistiocytosis, a disease that is clinically similar to MAS, highlight the possible pathogenetic role of a defective function of perforin, a protein involved in the cytolytic processes and control of lymphocyte proliferation. Although the clinical features of MAS have been well documented, early diagnosis can be difficult. Measurement of the serum ferritin level may assist in the diagnosis and may be a useful indicator of disease activity, therapy response, and prognosis. The recognition that MAS belongs to the secondary or reactive hemophagocytic syndromes has led to the proposal to rename it according to the contemporary classification of histiocytic disorders. Cyclosporin A has been found effective in patients with corticosteroid-resistant MAS. A recent report has suggested that etanercept may be a useful adjunctive therapeutic agent.

Neonatal mycobacterial specific cytotoxic T-lymphocyte and cytokine profiles in response to distinct BCG vaccination strategies

This study evaluated whether different bacillus Calmette-Guérin (BCG) strains, routes of administration, vaccination age and percutaneous tools influenced immune responses to BCG vaccination in infants. Proliferative responses, cytokine production and cell-mediated cytotoxicity obtained in post-vaccinated children were compared to baseline cord bloods and unvaccinated 10-week-old infants. BCG vaccination generally induced strong lymphoproliferative and T helper type 1 (Th1)-type cytokine responses. There was a trend for greater responsiveness following the intradermal route of vaccination, with Japanese-172 strain and with delaying vaccination until 10 weeks. Cord mononuclear cells differentially stimulated the Th2-type cytokines interleukin-5 (IL-5) and IL-10 selectively in response to BCG, as compared to H37Rv or purified protein derivative stimulation. We document for the first time the generation of mycobacterium-specific cytotoxic T lymphocytes in neonates, following BCG vaccination. Cytotoxic activity correlated with the ratio of interferon-gamma to IL-5, aside from a single instance where use of the Biovac tool resulted in a striking dissociation selectively against H37Rv targets. These data have implications for correlates of protective immunity in design of vaccine studies.

Epidermal powder immunization induces both cytotoxic T-lymphocyte and antibody responses to protein antigens of influenza and hepatitis B viruses

Cytotoxic T lymphocytes (CTL) play a vital role in host defense against viral and intracellular bacterial infections. However, nonreplicating vaccines administered by intramuscular injection using a syringe and needle elicit predominantly humoral responses and not CTL responses. Here we report that epidermal powder immunization (EPI), a technology that delivers antigens on 1.5- to 2.5-microm gold particles to the epidermis using a needle-free powder delivery system, elicits CTL responses to nonreplicating antigens. Following EPI, a majority of the antigen-coated gold particles were found in the viable epidermis in the histological sections of the target skin. Further studies using transmission electron microscopy revealed the intracellular localization of the gold particles. Many Langerhans cells (LCs) at the vaccination site contained antigen-coated particles, as revealed by two-color immunofluorescence microscopy, and these cells were found in the draining lymph nodes 20 h later. Immune responses to several viral protein antigens after EPI were studied in mice. EPI with hepatitis B surface antigen (HBsAg) and a synthetic peptide of influenza virus nucleoprotein (NP peptide) elicited antigen-specific CTL responses as well as antibody responses. In an in vitro cell depletion experiment, we demonstrated that the CTL activity against HBsAg elicited by EPI was attributed to CD8(+), not CD4(+), T cells. As controls, needle injections of HBsAg or the NP peptide into deeper tissues elicited solely antibody, not CTL, responses. We further demonstrated that EPI with inactivated A/Aichi/68 (H3N2) or A/Sydney/97 (H3N2) influenza virus elicited complete protection against a mouse-adapted A/Aichi/68 virus. In summary, EPI directly delivers protein antigens to the cytosol of the LCs in the skin and elicits both cellular and antibody responses.

Alterations in molecular killing mechanisms: implications in skin disease

Cytolytic T lymphocytes exert two main specific molecular killing mechanisms against target cells, namely (i) they can synthesize and release soluble cytolytic factors, and (ii) they can express effector molecules that act as ligands of receptors expressed by target cells on the cell surface; by these two pathways cytolytic T lymphocytes kill several targets, e.g. cells infected with intracellular pathogens, cells transformed by malignancy and cells producing autoantibodies. This review investigates the contribution from alterations in these molecular killing mechanisms to the pathogenesis of cutaneous diseases. In fact, molecular components involved in such killing mechanisms are often altered or distorted in skin pathology, e.g. cutaneous viral infections, skin cancer, contact hypersensitivity and autoimmune diseases with cutaneous involvement. Treatments capable of repairing the molecular components operating in such killing mechanisms could presumably favour the resolution of these skin diseases.

DNA immunization of HLA transgenic mice with a plasmid expressing mycobacterial heat shock protein 65 results in HLA class I- and II-restricted T cell responses that can be augmented by cytokines

Infection with Mycobacterium tuberculosis (MTB) remains a major cause of morbidity and mortality world-wide. An effective vaccination strategy is the immunization with plasmid DNA (pDNA), expressing an antigen (Ag) from a pathogen in vivo, which results in specific immune response against the encoded protein as well as the pathogen itself or cells infected with it. To test the ability to induce HLA-restricted T cell immune response against a mycobacterial antigen in humans by pDNA vaccination, we have used transgenic mice that express HLA class I (A*0201/Kb) or HLA class II (DRB1*0301) molecules. pDNA immunization with mycobacterial heat shock protein 65 (Mhsp65)-expressing plasmid (P3M.65) resulted in HLA-II-restricted, Ag-specific T cell-mediated immune responses characterized by proliferation and cytokine production. These T cell responses could be further augmented by the coinjection of P3M.65 and plasmid expressing murine GM-CSF. Furthermore, coimmunizing HLA-I transgenic mice with P3M.65 and a plasmid expressing murine IFN-gamma induced a specific cytotoxic T lymphocyte response restricted by HLA-A2. These results represent the first evidence of a concomitant in vivo induction of HLA class I- as well as class II-restricted T cell responses by pDNA immunization, which is induced or augmented by the codelivery of cytokine-expressing plasmids, supporting its potential use in clinical trials.

The balance between protective immunity and pathogenesis in tropical theileriosis: what we need to know to design effective vaccines for the future

The tick-borne protozoan parasite, Theileria annulata, causes an overwhelming disease in Friesian cattle, imported to improve productivity, in a large area of the world. The parasite invades bovine macrophages and induces aberrant changes which seem pivotal in triggering disease in naïve susceptible animals: parasite infected cells acquire dendritic cell features and over-activate CD4+ and CD8+ T cells. Elevated levels of interferon-gamma (IFN-gamma) are induced and B cells are developmentally arrested in the light zone of germinal centres. Infected macrophages are refractory to the effects of IFN-gamma and indeed flourish in its presence. High levels of pro-inflammatory cytokines, as evinced by high acute phase protein responses, probably also play a role in pathology. However, animals can become immune to further challenge. Cellular immune responses involving macrophages, natural killer cells and CD8+ T cells play a major role in recovery and subsequent maintenance of immunity. The main target for immunity appears to be the parasite infected macrophage, as attenuated cell lines can protect and are used as vaccines. Cloned lines selected for low cytokine production protect with no associated pathological reactions. Theileria annulata causes a relatively mild disease in an indigenous breed of cattle, which is associated with lower acute phase protein responses (controlled by macrophage cytokines). Thus the initial host-parasite interactions must determine the balance between immunity and pathogenesis. New generation vaccines to T. annulata should both induce active immunity and suppress pathology.

Classically restricted human CD8+ T lymphocytes derived from Mycobacterium tuberculosis-infected cells: definition of antigenic specificity

Previous studies in murine and human models have suggested an important role for HLA Ia-restricted CD8(+) T cells in host defense to Mycobacterium tuberculosis (Mtb). Therefore, understanding the Ags presented via HLA-Ia will be important in understanding the host response to Mtb and in rational vaccine design. We have used monocyte-derived dendritic cells in a limiting dilution analysis to generate Mtb-specific CD8(+) T cells. Two HLA-Ia-restricted CD8(+) T cell clones derived by this method were selected for detailed analysis. One was HLA-B44 restricted, and the other was HLA-B14 restricted. Both were found to react with Mtb-infected, but not bacillus Calmette-Guérin-infected, targets. For both these clones, the Ag was identified as culture filtrate protein 10 (CFP10)/Mtb11, a 10.8-kDa protein not expressed by bacillus Calmette-Guérin. Both clones were inhibited by the anti-class I Ab and anti-HLA-B,C Abs. Using a panel of CFP10/Mtb11-derived 15-aa peptides overlapping by 11 aa, the region containing the epitopes for both clones has been defined. Minimal 10-aa epitopes were defined for both clones. CD8(+) effector cells specific for these two epitopes are present at high frequency in the circulating pool. Moreover, the CD8(+) T cell response to CFP10/Mtb11 can be largely accounted for by the two epitopes defined herein, suggesting that this is the immunodominant response for this purified protein derivative-positive donor. This study represents the first time CD8(+) T cells generated against Mtb-infected APC have been used to elucidate an Mtb-specific CD8(+) T cell Ag.

Restoration of cellular immunity against tuberculosis in patients coinfected with HIV-1 and tuberculosis with effective antiretroviral therapy: assessment by determination of CD69 expression on T cells after tuberculin stimulation

Whether immunity against opportunistic pathogens can be fully restored by control of HIV-1 replication remains open to question. This longitudinal study was conducted to measure anti-tuberculosis (TB) cellular immunity in 13 HIV-1/TB-coinfected patients effectively treated by highly active antiretroviral therapy (HAART) in a period of 12 months. In this study, anti-TB cellular immunity was assessed by determining the frequencies of CD 69 expression on CD4+ and CD8+ T cells in response to purified protein derivative (PPD) stimulation (abbreviated as %CD4+CD69 to PPD and %CD8+CD69 to PPD). Here, we show that %CD4+CD69 to PPD correlated with the results of tuberculin skin tests and interferon-gamma (IFN-gamma) production from PPD-stimulated CD4+ T cells, and %CD8+CD69 to PPD also correlated with CD8+ T cell-mediated PPD-specific cytolysis. In overall analysis for these 13 patients, both %CD4+CD69 to PPD and %CD8+CD69 to PPD increased significantly during the 12 months (p =. 003 and p <.001, respectively). However, we found %CD4+CD69 to PPD or %CD8+CD69 to PPD failed to increase substantially in some patients (i.e., immunologic nonresponders). A significantly higher proportion of patients whose baseline CD4+ count was <50 cells/mm3 were considered to be CD4+ nonresponders compared with those whose baseline CD4+ count was >50 cells/mm3. Furthermore, baseline CD4+ cell count in nonresponders is significantly lower than that in responders, although the effectiveness of HAART did not differ between them. Our results indicate that PPD-specific frequencies of CD69 expression may be used as surrogate markers of anti-TB cellular immunity. By this method, we show that full reconstitution of anti-TB cellular immunity in HIV-1/TB coinfected patients may not necessarily be achieved by "successful" HAART and may be influenced by the baseline immune status when HAART is started. These data suggest that the decision to discontinue secondary prophylaxis for opportunistic infections should be cautiously made, even when the CD4+ cell count has significantly increased.

Host immune response to intracellular bacteria: A role for MHC-linked class-Ib antigen-presenting molecules

MHC-linked class-Ib molecules are a subfamily of class-I molecules that display limited genetic polymorphism. At one time these molecules were considered to have an enigmatic function. However, recent studies have shown that MHC-linked class-Ib molecules can function as antigen presentation structures that bind bacteria-derived epitopes for recognition by CD8+ effector T cells. This role for class-Ib molecules has been demonstrated across broad classes of intracellular bacteria including Listeria moncytogenes, Salmonella typhimurium, and Mycobacterium tuberculosis. Additionally, evidence is emerging that MHC-linked class-Ib molecules also serve an integral role as recognition elements for NK cells as well as several TCR alpha/beta and TCR gamma/delta T-cell subsets. Thus, MHC-linked class-Ib molecules contribute to the host immune response by serving as antigen presentation molecules and recognition ligands in both the innate and adaptive immune response to infection. In this review, we will attempt to summarize the work that supports a role for MHC-linked class-Ib molecules in the host response to infection with intracellular bacteria.

Induction of antibody and T-cell responses by immunization with ISCOMS containing the 38-kilodalton protein of Mycobacterium tuberculosis

In this study, we investigated the influence of different amounts of N-(palmitoyloxy) succinimide (PA-NHS): attachment of lipid tails to the protein and Quil A on the immunogenicity of the 38-kDa mycobacterial protein incorporated into immunostimulating complexes (ISCOMS; 38-kDa ISCOMS). The addition of higher amounts of Quil A during the ISCOMS preparation increased the amount of protein incorporated into ISCOMS, whereas the use of higher amounts of PA did not influence this parameter. Low antibody responses were observed after primary immunization with all 38-kDa ISCOMS preparations which, however, strongly increased after booster injections. IgG2a is the major subclass IgG induced by these ISCOMS preparations. There were only slight differences between the various ISCOMS formulations in their capacity to induce cytotoxic T-lymphocytes (CTLs). Spleen cells primed with ISCOMS prepared with the highest amount of Quil A produced high levels of IFN-gamma after stimulation with T helper cell type one (Th1) peptide of the 38-kDa protein (aa 70-84), 38-kDa protein or purified protein derivate (PPD). Spleen cells primed with ISCOMS prepared with the lowest amount of Quil A only substantial IFN-gamma levels were detected after stimulation with 38-kDa protein. IL-4 secretion was very low or not detectable with all ISCOM preparations. These results therefore demonstrated that all 38 kDa-ISCOMS preparations were: (1) immunogenic by inducing antibodies, Th1 and CTL responses; (2) that the way in which the ISCOMS were prepared, e.g. the amount of Quil A used, modulates the epitope specificity of the Th1 response.

Development of semisynthetic triterpenoid saponin derivatives with immune stimulating activity

Aldehyde-containing triterpene saponins have adjuvant properties, but only those from Quillaja saponaria Molina stimulate the production of cytotoxic T lymphocytes (CTL) against exogenous antigens. Quillaja saponins have two normonoterpene ester moieties, linked linearly to their fucosyl residue, that play a critical role in the stimulation of CTL. These ester moieties are also responsible for these saponins' instability and toxicity. Based on the structure-activity relationships for the different groups of Q. saponaria saponins, new semi-synthetic analogs were developed that have the adjuvanticity of quillaja saponins, yet with less toxicity and greater stability in aqueous solutions. The quillaja saponin analogs were prepared by replacing their hydrolytically unstable ester groups with another lipophilic chain linked by a stable amide bond on these saponins' glucuronic acid residue. One of these analogs, GPI-0100, is a dodecylamide saponin derivative that stimulates an antibody isotype profile that corresponds to a Th1 type immune response, as well as CTL production against exogenous antigens.

Mycobacterium tuberculosis-reactive CD8+ T lymphocytes: the relative contribution of classical versus nonclassical HLA restriction

Previous studies in mice and humans models have suggested an important role for CD8+ T cells in host defense to Mycobacterium tuberculosis (Mtb). In humans, CD8+ Mtb-reactive T cells have been described that are HLA-A2-, B52-, as well as CD1-restricted. Recently, we have described Mtb-specific CD8+ T cells that are neither HLA-A-, B-, or C- nor group 1 CD1-restricted. At present, little is known about the relative contribution of each of these restriction specificities to the overall CD8+ response to Mtb. An IFN-gamma enzyme-linked immunospot assay was used to determine the frequency of Mtb-reactive CD8+ T cells directly from PBMC. The effector cell frequency among five healthy purified protein derivative-positive subjects was 1/7,600 +/- 4,300 compared with 1/16,000 +/- 7,000 in six purified protein derivative-negative controls. To determine the frequencies of classically, CD1-, and nonclassically restricted cells, a limiting dilution analysis was performed. In one purified protein derivative-positive subject, 192 clones were generated using Mtb-infected dendritic cells (DC). Clones were assessed for reactivity against control autologous DC, Mtb-infected autologous DC, and HLA-mismatched CD1+ targets (DC), as well as HLA-mismatched CD1- targets (macrophages). Of the 96 Mtb-reactive CD8+ T cell clones, four (4%) were classically restricted and 92 (96%) were nonclassically restricted. CD1-restricted cells were not detected. Of the classically restricted cells, two were HLA-B44 restricted and one was HLA-B14 restricted. These results suggest that while classically restricted CD8+ lymphocytes can be detected, they comprise a relatively small component of the overall CD8+ T cell response to Mtb. Further definition of the nonclassical response may aid development of an effective vaccine against tuberculosis.

Why do cultured transplanted myoblasts die in vivo? DNA quantification shows enhanced survival of donor male myoblasts in host mice depleted of CD4+ and CD8+ cells or Nk1.1+ cells

Overcoming the massive and rapid death of injected donor myoblasts is the primary hurdle for successful myoblast transfer therapy (MTT), designed as a treatment for the lethal childhood myopathy Duchenne muscular dystrophy. The injection of male myoblasts into female host mice and quantification of surviving male DNA using the Y-chromosome-specific (Y1) probe allows the speed and extent of death of donor myoblasts to be determined. Cultured normal C57BL/10Sn male donor myoblasts were injected into untreated normal C57BL/10Sn and dystrophic mdx female host mice and analyzed by slot blots using a 32P-labeled Y1 probe. The amount of male DNA from donor myoblasts showed a remarkable decrease within minutes and by 1 h represented only about 10-18% of the 2.5 x 10(5) cells originally injected (designated 100%). This declined further over 1 week to approximately 1-4%. The host environment (normal or dystrophic) as well as the extent of passaging in tissue culture (early "P3" or late "P15-20" passage) made no difference to this result. Modulation of the host response by CD4+/CD8+ -depleting antibodies administered prior to injection of the cultured myoblasts dramatically enhanced donor myoblast survival in dystrophic mdx hosts (15-fold relative to untreated hosts after 1 week). NK1.1 depletion also dramatically enhanced donor myoblast survival in dystrophic mdx hosts (21-fold after 1 week) compared to untreated hosts. These results provide a strategic approach to enhance donor myoblast survival in clinical trials of MTT.

Evaluation of T-cell responses to peptides and lipopeptides with MHC class I binding motifs derived from the amino acid sequence of the 19-kDa lipoprotein of Mycobacterium tuberculosis

Cytotoxic T-lymphocyte (CTL) epitopes on the 19-kDa lipoprotein from Mycobacterium tuberculosis were identified by the use of lipopeptides and their cytokine profile studied. Selection of candidate CTL epitopes was based on synthetic peptides derived from the amino acid sequence of the 19-kDa lipoprotein showing major histocompatibility complex class I (MHC-I) binding motifs (H-2D(b) and H-2L(d)). Their ability to up-regulate and stabilize MHC-I molecules on the mouse lymphoma cell line RMA-S was studied. Similar studies were performed with peptides, in which the anchor amino acid of the H-2D(b) MHC-I motif was replaced by alanine. Three out of five peptides with H-2D(b) or H-2L(d) binding motifs and their corresponding lipopeptides as well, up-regulated and stabilized the H-2D(b) molecules on RMA-S cells. Replacement of the anchor amino acid residues of the H-2D(b) MHC-I motif by alanine revealed that the anchor amino acid asparagine at position 5, contributed more to binding of peptide to H-2D(b) molecules than leucine at position 11. The closely related lipopeptides LP19c and LP19d, in combination with incomplete Freund's adjuvant (IFA), induced CTL responses in C57BL/6 (H-2(b)) mice. These CTLs could recognize the naturally processed antigen, i.e. the 19-kDa antigen protein produced and processed by the EX-19 cell line. The capacity of the various lipopeptides to induce CTL correlated well with the ability of the (lipo)peptide to up-regulate and to stabilize H-2D(b) molecules. Lipopeptide LP19c primed spleen cells showed a T helper type one profile after in vitro stimulation with P19c and P19d 19 kDa peptides. The approach to characterize presumptive 19-kDa CTL epitopes might lead to selection of promising CTL epitopes, which can be applied in the development of subunit tuberculosis vaccines.

Immunobiology and the future of myoblast transfer therapy

Myoblast transfer therapy (MTT) is a cell-mediated gene transfer method aimed at the restoration of normal dystrophin expression in Duchenne muscular dystrophy (DMD). Initial clinical MTT trials were conducted amid much controversy, as they were based on very few animal studies. Unfortunately, the trials were of little therapeutic benefit. As a result, there has been a renaissance of interest in experimental studies in animal models. In MTT, myoblasts are obtained by muscle biopsy from normal, i.e., dystrophin-positive, donors, expanded in culture, and injected directly into the muscles of dystrophic recipients. The major requirement for successful MTT is the survival of injected donor myoblasts in the host environment. However, a vast majority of donor cells fail to survive for more than 1 h after injection, and very few last beyond the first week. This review on the immunological aspects of MTT focuses in particular on the roles of specific components of the host immune response, the effects of tissue culture on donor cells, and strategies under development to circumvent the problem of donor myoblast death after injection in vivo.

Equine immunity to bacteria

The remarkable ability of the horse and other animals to prevent infection by most bacterial pathogens encountered is the result of a complex set of distinct but overlapping defense mechanisms. This article summarizes the current state of knowledge on innate and adaptive immunity to bacterial pathogens and reviews various ways in which some bacteria have evolved in order to evade components of the host response.

Activated Lymphocytes Promote Endothelial Cell Detachment from Matrix: A Role for Modulation of Endothelial Cell β1 Integrin Affinity

In vivo, MHC class I-restricted injury of allogeneic tissue or cells infected by intracellular pathogens occurs in the absence of classical cytolytic effector mechanisms and Ab. Modulation of the target cell adhesion to matrix may be an additional mechanism used to injure vascular or epithelial cells in inflammation. We studied the mechanisms of human umbilical vein endothelial cell (EC) detachment from matrix-coated plastic following contact by concanamycin A-treated lymphocytes as an in vitro model of perforin-independent modulation of EC basement membrane adhesion. Human PBL were depleted of monocytes, stimulated, then added to an EC monolayer plated on either fibronectin or type I collagen matrices. Activated, but not resting, PBL induced progressive EC detachment from the underlying matrix. Injury of the EC monolayer required direct cell contact with the activated lymphocytes because no detachment was seen when the PBL were placed above a Transwell membrane. Moreover plasma membranes prepared from activated but not resting PBL induced EC detachment. Adherent EC stimulated with activated PBL did not show evidence of apoptosis using TUNEL and annexin V staining at time points before EC detachment was observed. Finally, neither the matrix metalloproteinase inhibitors o-phenanthroline and BB-94 nor aprotinin blocked EC detachment. However, activation of EC β1 integrin using mAb TS2/16 or Mg2+ decreased EC detachment. These data indicate that cell-cell contact between activated PBL and EC reduces adhesion of EC to the underlying matrix, at least in part by inducing changes in the affinity of the endothelial β1 integrin.

Attenuated host resistance against Mycobacterium bovis BCG infection in mice lacking osteopontin

Expression of the cytokine osteopontin (OPN) is elevated in granulomas caused by Mycobacterium tuberculosis. We tested the hypothesis that OPN contributes to host protection in a mouse model of mycobacterial infection. When infected with Mycobacterium bovis BCG, mice lacking a functional OPN gene had more severe infections characterized by heavier bacterial loads and a delayed clearance of the bacteria. The OPN-null mice had greater granuloma burdens consistent with the elevated bacterial load. The ability of osteopontin to facilitate the clearance of mycobacteria was most pronounced early after infection and appeared to be independent of known mediators of resistance to infection by mycobacteria: antigen-specific T-cell immunity, gamma interferon production, and nitric oxide production. BCG grew more rapidly in macrophages derived from OPN-null mice than in those from wild-type mice, demonstrating that the null phenotype was due to an intrinsic macrophage defect. These results indicate that osteopontin augments the host response against a mycobacterial infection and that it acts independently from other antimycobacterial resistance mechanisms.

T cell responses to bacterial infection

Many exciting advances in our understanding of T cell mediated immunity to bacterial infection have occurred in the past several years. T cell responses have been more fully characterized, due in part to the development of MHC class I tetramers. The importance of cytokines and various effector molecules in defense against infection has come to light. Finally, intracellular bacteria are being exploited to deliver antigens and DNA in an effort to induce immunity to pathogens.