Specific lysis of mycobacterial antigen-bearing macrophages by class II MHC-restricted polyclonal T cell lines in healthy donors or patients with tuberculosis

Miliary Tuberculosis

Miliary tuberculosis (TB) results from a massive lymphohematogenous dissemination of Mycobacterium tuberculosis bacilli and is characterized by tiny tubercles evident on gross pathology resembling millet seeds in size and appearance. The global HIV/AIDS pandemic and widespread use of immunosuppressive drugs and biologicals have altered the epidemiology of miliary TB. Considered to be predominantly a disease of infants and children in the pre-antibiotic era, miliary TB is increasingly being encountered in adults as well. The clinical manifestations of miliary TB are protean and nonspecific. Atypical clinical presentation often delays the diagnosis. Clinicians, therefore, should have a low threshold for suspecting miliary TB. Focused, systematic physical examination helps in identifying the organ system(s) involved, particularly early in TB meningitis, as this has therapeutic significance. Fundus examination for detecting choroid tubercles offers a valuable clinical clue for early diagnosis, as their presence is pathognomonic of miliary TB. Imaging modalities help in recognizing the miliary pattern, defining the extent of organ system involvement. Examination of sputum, body fluids, image-guided fine-needle aspiration cytology or biopsy from various organ sites, needle biopsy of the liver, bone marrow aspiration, and biopsy should be done to confirm the diagnosis. Cytopathological, histopathological, and molecular testing (e.g., Xpert MTB/RIF and line probe assay), mycobacterial culture, and drug susceptibility testing must be carried out as appropriate and feasible. Miliary TB is uniformly fatal if untreated; therefore, early initiation of specific anti-TB treatment can be lifesaving. Monitoring for complications, such as acute kidney injury, air leak syndromes, acute respiratory distress syndrome, adverse drug reactions such as drug-induced liver injury, and drug-drug interactions (especially in patients coinfected with HIV/AIDS), is warranted.

Miliary tuberculosis: A new look at an old foe

Miliary tuberculosis (TB), is a fatal form of disseminated TB characterized by tiny tubercles evident on gross pathology similar to innumerable millet seeds in size and appearance. Global HIV/AIDS pandemic and increasing use of immunosuppressive drugs have altered the epidemiology of miliary TB. Keeping in mind its protean manifestations, clinicians should have a low threshold for suspecting miliary TB. Careful physical examination should focus on identifying organ system involvement early, particularly TB meningitis, as this has therapeutic significance. Fundus examination for detecting choroid tubercles can help in early diagnosis as their presence is pathognomonic of miliary TB. Imaging modalities help in recognizing the miliary pattern, define the extent of organ system involvement and facilitate image guided fine-needle aspiration cytology or biopsy from various organ sites. Sputum or BAL fluid examination, pleural, pericardial, peritoneal fluid and cerebrospinal fluid studies, fine needle aspiration cytology or biopsy of the lymph nodes, needle biopsy of the liver, bone marrow aspiration and biopsy, testing of body fluids must be carried out. GeneXpert MTB/RIF, line probe assay, mycobacterial culture and drug-susceptibility testing must be carried out as appropriate and feasible. Treatment of miliary TB should be started at the earliest as this can be life saving. Response to first-line anti-TB drugs is good. Screening and monitoring for complications like acute respiratory distress syndrome (ARDS), adverse drug reactions like drug-induced liver injury, drug-drug interactions, especially in patients co-infected with HIV/AIDS, are warranted. Sparse data are available from randomized controlled trials regarding optimum regimen and duration of anti-TB treatment.

Challenges in the diagnosis & treatment of miliary tuberculosis

Miliary tuberculosis (TB) is a potentially lethal disease if not diagnosed and treated early. Diagnosing miliary TB can be a challenge that can perplex even the most experienced clinicians. Clinical manifestations are nonspecific, typical chest radiograph findings may not be evident till late in the disease, high resolution computed tomography (HRCT) shows randomly distributed miliary nodules and is relatively more sensitive. Ultrasonography, CT and magnetic resonance imaging (MRI) are useful in discerning the extent of organ involvement by lesions of miliary TB in extra-pulmonary locations. Fundus examination for choroid tubercles, histopathological examination of tissue biopsy specimens, conventional and rapid culture methods for isolation of Mycobacterium tuberculosis, drug-susceptibility testing, along with use of molecular biology tools in sputum, body fluids, other body tissues are useful in confirming the diagnosis. Although several prognostic markers have been described which predict mortality, yet untreated miliary TB has a fatal outcome within one year. A high index of clinical suspicion and early diagnosis and timely institution of anti-tuberculosis treatment can be life-saving. Response to first-line anti-tuberculosis drugs is good but drug-induced hepatotoxicity and drug-drug interactions in human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) patients pose significant problems during treatment. However, sparse data are available from randomized controlled trials to define the optimum regimen and duration of treatment in patients with drug-sensitive as well as drug-resistant miliary TB, including those with HIV/AIDS.

Granulysin-expressing CD4+ T cells as candidate immune marker for tuberculosis during childhood and adolescence

Background

Granulysin produced by cytolytic T cells directly contributes to immune defense against tuberculosis (TB). We investigated granulysin as a candidate immune marker for childhood and adolescent TB.

Methods

Peripheral blood mononuclear cells (PBMC) from children and adolescents (1–17 years) with active TB, latent TB infection (LTBI), nontuberculous mycobacteria (NTM) infection and from uninfected controls were isolated and restimulated in a 7-day restimulation assay. Intracellular staining was then performed to analyze antigen-specific induction of activation markers and cytotoxic proteins, notably, granulysin in CD4⁺ CD45RO⁺ memory T cells.

Results

CD4⁺ CD45RO⁺ T cells co-expressing granulysin with specificity for Mycobacterium tuberculosis (Mtb) were present in high frequency in TB-experienced children and adolescents. Proliferating memory T cells (CFSE_lowCD4⁺CD45RO⁺) were identified as main source of granulysin and these cells expressed both central and effector memory phenotype. PBMC from study participants after TB drug therapy revealed that granulysin-expressing CD4⁺ T cells are long-lived, and express several activation and cytotoxicity markers with a proportion of cells being interferon-gamma-positive. In addition, granulysin-expressing T cell lines showed cytolytic activity against Mtb-infected target cells.

Conclusions

Our data suggest granulysin expression by CD4⁺ memory T cells as candidate immune marker for TB infection, notably, in childhood and adolescence.

Characterization of effector functions of human peptide-specific CD4+ T-cell clones for an intracellular pathogen

CD4+ T cells are believed to play a dominant role in human defenses against Mycobacterium tuberculosis through production of interferon (IFN)-gamma, cytolytic T-cell (CTL) activity, and inhibition of intracellular mycobacterial growth. Most functional studies of CD4+ cells have used bulk T-cells that recognize crude mycobacterial antigens, and the functional capacity of individual human T cells is not well defined. We studied the functional capacity of human CD4+ T-cell clones that recognize a specific mycobacterial peptide. Clone B9 produced high concentrations of IFN-gamma and exhibited potent CTL activity, whereas clone D3 produced IFN-gamma but showed poor CTL activity. The CTL activity of clone B9 was inhibited by SrCl(2) and concanamycin A but not by anti-Fas antibodies. Clone B9 also reduced the mycobacterial burden in dendritic cells by more than 90%, and this antimycobacterial activity was inhibited by SrCl(2) and concanamycin A. We conclude that: (1) individual human peptide-specific CD4+ T-cell clones have differential capacity to produce Th1 cytokines and to lyse M tuberculosis-infected target cells; and (2) both granulysin and perforin contribute to the capacity of human CD4+ T-cells to lyse infected targets and to inhibit intracellular mycobacterial growth.

IFN-gamma regulates Fas ligand expression in human CD4+ T lymphocytes and controls their anti-mycobacterial cytotoxic functions

Fas and Fas Ligand (FasL) expression, activation-induced cell death (AICD) and mycobacterial antigen-specific cytotoxicity of peripheral T cells from patients with complete inherited IFN-gamma receptor 1 binding chain deficiency (IFN-gammaR1-/-) were investigated. Fas was equally expressed in both normal and deficient T lymphoblasts and they underwent apoptosis when stimulated with agonist anti-Fas mAb. By contrast, T lymphoblasts and CD4+ T cell clones (TCC) from deficient patients displayed a reduced surface FasL expression and resistance to AICD. CD8+ TCC from healthy and deficient patients displayed similar high level of FasL and susceptibility to AICD. In Jurkat CD4+ T cells competent to transduce IFN-gamma signaling, IFN-gamma induced surface FasL export and their Fas-dependent apoptosis. Effector T cells generated from a patient with a dominant negative mutation of IFN-gammaR1 (IFN-gammaR1DN) following stimulation with mycobacterial antigens were unable to kill MHC class II-matched, mycobacterial antigen-pulsed macrophages. Normal Fas expression in T cells and FasL in CD8+ cells may account for the absence of autoimmune disorders in these patients. Conversely, defective FasL expression on IFN-gammaR1DN CD4+ T cells impairs their cytotoxic functions and highlights a novel role for IFN-gamma signaling in the control of mycobacterial infection in humans.

Evaluation of T-cell responses to peptides with MHC class I-binding motifs derived from PE_PGRS 33 protein of Mycobacterium tuberculosis

The PE and PPE proteins of Mycobacterium tuberculosis form a source of antigenic variation among different strains of M. tuberculosis. One of the PE_PGRS proteins, Rv1818c, plays a role in the pathogenesis of mycobacterial infection and specifically influences host-cell responses to tuberculosis infection. Although little is known about these two classes of protein, an immunoinformatics approach has indicated the possibility of their participation in eliciting a major histocompatibility complex (MHC) class I-mediated immune response against tuberculosis, as peptides derived from Rv1818c are predicted to bind to MHC class I molecules with high affinity. In the present work, a DNA vaccine was constructed encoding the full-length Rv1818c protein of M. tuberculosis and its immunogenicity was analysed in BALB/c mice. Immunization with Rv1818c DNA induced a strong CD8+ cytotoxic lymphocyte and Th1-type response, with high levels of gamma interferon (IFN-gamma) and low levels of interleukin-4. Two nonameric peptides (Peptide(6-14) and Peptide(385-393)) from Rv1818c were identified by their ability to induce the production of IFN-gamma by CD8+ T cells in mice immunized with Rv1818c DNA. An epitope-specific response was demonstrated by the lysis of peptide-pulsed antigen-presenting cells, release of cytotoxic granules and IFN-gamma production. These peptides bound with high affinity to MHC H-2K(d) and showed low dissociation rates of peptide-MHC complexes. These results could form the basis for testing the identified T-cell epitopes of PE_PGRS proteins in the induction of protective immunity against M. tuberculosis challenge in the mouse model.

Increased serum level of vascular endothelial growth factor in Mycobacterium avium complex infection

OBJECTIVE

Pulmonary infection caused by Mycobacterium avium complex (MAC) is one of the granulomatous diseases which are associated with the expression of vascular endothelial growth factor (VEGF). The aim of the present study was to clarify the association of VEGF with the pathogenesis of MAC infection.

METHODOLOGY

The serum VEGF levels in 46 patients with pulmonary MAC infection were compared with those in 16 normal control subjects. Pulmonary lesions were evaluated using chest CT. In 20 patients, after treatment, serum VEGF levels were measured and chest CT performed again to evaluate pulmonary response to treatment.

RESULTS

Infected patients had higher serum VEGF levels than controls (435.2 +/- 29.1 vs. 167.0 +/- 10.6 pg/mL, P < 0.0001), and serum VEGF level correlated with the extent of disease. The serum VEGF levels in 14 patients who underwent treatment and exhibited an improvement in their pulmonary lesions decreased significantly compared with the results pretreatment (509.0 +/- 60.7 vs. 303.6 +/- 65.3 pg/mL, P = 0.0092). In infected patients, alveolar macrophages, epithelioid cells and multinucleated giant cells exhibited VEGF overexpression on immunohistochemical staining.

CONCLUSIONS

This study suggests that VEGF may be associated with the pathogenesis of pulmonary MAC infection. Additionally, serum VEGF levels may be a useful surrogate marker for evaluating the extent of disease and of the response to treatment.

Immunodominance of low molecular weight secretory polypeptides of Mycobacterium tuberculosis to induce cytotoxic T-lymphocyte response

The cytotoxic T-lymphocyte (CTL) responses to culture filtrate antigens of Mycobacterium tuberculosis H(37)Rv (RvCFP) and purified protein derivative (PPD) were investigated in active pulmonary tuberculosis patients, healthy tuberculosis contacts and non-contacts. Healthy tuberculin skin test (Mantoux) positive tuberculosis contacts demonstrated strong CTL response against RvCFP and Mantoux reactivity was found to correlate with CTL response. The specificity of CTL response in healthy Mantoux positive contacts was further assessed using different molecular weight fractions of RvCFP. Peripheral blood mononuclear cells (PBMCs) derived CTLs recognized multiple antigenic targets and demonstrated predominant cytotoxicity against low molecular weight (below 15 kDa) protein fractions as well as those migrated in the region of 30 kDa. Subsequently, evaluation of CTL responses against selected purified prominent T-cell antigens indicated maximum CTL response directed against Ag 85 complex proteins; most notably Ag 85 A. From this study, it is suggested that identification of more mycobacterial antigens activating various CTL subsets could be an important step for the rational designing of future antituberculous vaccine.

Miliary tuberculosis: new insights into an old disease

Miliary tuberculosis is a potentially lethal form of tuberculosis resulting from massive lymphohaematogeneous dissemination of Mycobacterium tuberculosis bacilli. The emergence of the HIV/AIDS pandemic and widespread use of immunosuppressive drugs has changed the epidemiology of miliary tuberculosis. Impaired cell-mediated immunity underlies the disease's development. Clinical manifestations are non-specific and typical chest radiographic findings may not be seen until late in the course of the disease. Atypical presentations--eg, cryptic miliary tuberculosis and acute respiratory distress syndrome--often delay the diagnosis. Several laboratory abnormalities with prognostic and therapeutic implications have been described, including pulmonary function and gas exchange impairment. Isolation of M tuberculosis from sputum, body fluids, or biopsy specimens, application of molecular methods such as PCR, and histopathological examination of tissue biopsy specimens are useful for the confirmation of diagnosis. Although response to first-line antituberculosis drugs is good, evidence regarding optimum duration of treatment is lacking and the role of adjunctive corticosteroid treatment is unclear.

Cytotoxic T-cell responses to Mycobacterium bovis during experimental infection of cattle with bovine tuberculosis

Cytotoxic T-cell responses are thought to play a significant role in the host defence against mycobacterial infections. Little is understood about such responses of cattle to Mycobacterium bovis, the causative agent of bovine tuberculosis. The work described in this report demonstrates the activity of cytotoxic cells during experimental infection of cattle with M. bovis. The cytotoxic cells were found to have the ability to specifically lyse macrophages infected with M. bovis and were detected in peripheral blood lymphocytes after in vitro re-exposure to M. bovis. Cytotoxic activity was detected 4 weeks after experimental infection with M. bovis; a similar level of activity was maintained during the infection and it was mediated by both WC1+gammadelta and CD8+ T cells. In addition, inhibition of the growth of M. bovis within infected macrophages was detected when they were exposed to cultures containing M. bovis-specific cytotoxic cells. The ability to detect cytotoxic cells after infection of cattle with M. bovis will allow their activity to be measured during vaccination trials. Correlation of cytotoxic activity with disease outcome may aid in the design of new vaccines and vaccination strategies.

Human immunity to M. tuberculosis: T cell subsets and antigen processing

A hallmark of M. tuberculosis infection is the ability of most (90-95%) healthy adults to control infection through acquired immunity, in which antigen specific T cells and macrophages arrest growth of M. tuberculosis bacilli and maintain control over persistent bacilli. In addition to CD4+ T cells, other T cell subsets such as, gammadelta, CD8+ and CD1-restricted T cells have roles in the immune response to M. tuberculosis. A diverse T cell response allows the host to recognize a wider range of mycobacterial antigens presented by different families of antigen-presenting molecules, and thus greater ability to detect the pathogen. Macrophages are key antigen presenting cells for T cells, and M. tuberculosis survives and persists in this central immune cell. This is likely an important factor in generating this T cell diversity. Furthermore, the slow growth and chronic nature of M. tuberculosis infection results in prolonged exposure to antigens, and hence further T cell sensitization. The effector mechanisms used by T cells to control M. tuberculosis are poorly understood. To survive in macrophages, M. tuberculosis has evolved mechanisms to block immune responses. These include modulation of phagosomes, neutralization of macrophage effector molecules, stimulating the secretion of inhibitory cytokines, and interfering with processing of antigens for T cells. The relative importance of these blocking mechanisms likely depends on the stage of M. tuberculosis infection: primary infection, persistence, reactivation or active tuberculosis. The balance of the host-pathogen interaction in M. tuberculosis infection is determined by the interaction of T cells and infected macrophages. The outcome of this interaction results either in control of M. tuberculosis infection or active disease. A better understanding of this interaction will result in improved approaches to treatment and prevention of tuberculosis.

Specific lytic activity against mycobacterial antigens is inversely correlated with the severity of tuberculosis

The ability of peripheral blood mononuclear cells (PBMC) from patients with active tuberculosis to display cytotoxic responses against autologous Mycobacterium tuberculosis (Mtb)-pulsed macrophages was evaluated. Non-MHC restricted cell-dependent lytic activity was observed in ex vivo effector cells from tuberculosis patients and was mediated mainly by CD3(+)gammadelta TCR(+) T (gammadelta T) cells bearing CD56 and/or CD16 molecules. MHC-restricted and non-MHC restricted cytotoxic T cells (CTL) were differentially expanded upon stimulation with Mtb in tuberculosis patients and normal controls (N). Class-I restricted CD8(+) CTL and class-II restricted CD4(+) CTL were generated in PPD(+)N and to a lesser extent in PPD(-)N. Mtb-stimulated effector cells from tuberculosis patients became progressively non-MHC restricted CD4(-)CD8(-)gammadelta T cells, while lytic activity of CD4(+) and CD8(+)CTL decreased gradually as the disease became more severe. On the other hand, target cells were lysed by ex vivo cells from tuberculosis patients through the Fas-FasL and perforin pathways. Mtb-induced CD4(+) CTL from tuberculosis patients and N controls preferentially employed the Fas-FasL mechanism. Mtb-induced CD8(+) CTL effector cells from patients used the perforin-based mechanism while cells from N controls also used the Fas-FasL pathway. While Mtb-induced gammadelta CTL from patients and PPD(-)N employed the latter mechanism cells from PPD(+)N individuals also used the perforin pathway. It can be concluded that shifts in the CTL response and the cytolytic mechanisms take place as the pulmonary involvement becomes more severe.

Purified protein derivative of tuberculin upregulates the expression of vascular endothelial growth factor in T lymphocytes in vitro

The purpose of this study was to investigate the cellular source and significance of vascular endothelial growth factor (VEGF) which, as reported previously, is elevated in the sera of pulmonary tuberculous patients. We obtained peripheral blood mononuclear cells (PBMCs) from 28 patients with active pulmonary tuberculosis, from 11 healthy controls who were positive for purified protein derivative of tuberculin (PPD), and from eight healthy individuals who were negative for PPD. We incubated the PBMCs with PPD in the presence or absence of major histocompatibility (MHC) class I or class II antibody in vitro, and measured the VEGF levels of culture supernatants. We also analysed the source of cells that secrete VEGF by using flow cytometry with intracellular staining. The T lymphocytes of active tuberculous patients secreted a higher level of VEGF than those of healthy controls. This production of VEGF was inhibited by adding MHC class II antibody. The addition of MHC class I antibody, however, did not inhibit. We propose that CD4+ T lymphocytes are almost certainly the cells that produce VEGF in response to PPD. VEGF production might be associated with an antigen-specific immune reaction via CD4+ T lymphocytes in tuberculosis.

A longitudinal study of in vitro IFNgamma production and cytotoxic T cell responses of tuberculosis patients in the gambia

SETTING

This study was carried out at the MRC Laboratories, The Gambia.

OBJECTIVES

To characterize the antigen-specific IFNgamma production and cytotoxic T cell (CTL) responses of patients during active tuberculosis, treatment, and following recovery.

DESIGN

PBMC were isolated from 37 patients with tuberculosis and incubated with either PPD, live M. bovis BCG, or no antigen and IFNgamma production measured after 7 days. CTL activity against these antigens was determined using autologous antigen-pulsed monocyte-derived macrophages as target cells. A subset of these patients (7-18 depending on antigen and assey used) were tested 2 months into drug treatment and 3 months after discharge. A group of blood bank donors (n= 21) were also tested to evaluate IFNgamma responses in endemic controls; a subset (n= 16) were also tested for CTL activity.

RESULTS

The ability to produce IFNgamma in response to mycobacterial antigens correlated with the Mantoux skin test status of the patient. IFNgamma production to live M. bovis BCG was diminished at diagnosis but returned after 2 months of drug treatment, and was sustained after completion of drug therapy. The CTL responses to both PPD and live M. bovis BCG were reduced during the period of drug treatment compared to those at diagnosis, but returned to the original levels after recovery.

CONCLUSIONS

Drug treatment induced marked alterations in the immune responses of tuberculosis patients with induction of IFNgamma production in response to stimulation with live M. bovis BCG. This may indicate activation of both CD4 and CD8 T cells.

Naive human T cells develop into Th1 effectors after stimulation with Mycobacterium tuberculosis-infected macrophages or recombinant Ag85 proteins

Most studies of human T-cell responses in tuberculosis have focused on persons with either active disease or latent infection. Although this work has been critical in defining T-cell correlates of successful versus failed host containment, little is known about the development of Mycobacterium-specific T-cell responses in uninfected persons. To explore this issue, naive T cells from uninfected donors were sensitized in vitro with avirulent Mycobacterium tuberculosis-infected autologous macrophages. T-cell lines primed in this manner proliferated and produced cytokines after challenge with mycobacterial antigens. Of 11 such lines, 8 were high Th1 responders, 2 were low Th1 responders, and 1 was a Th2 responder. Furthermore, similar patterns and magnitudes of proliferative and cytokine responses were seen when Mycobacterium infection-primed lines were challenged with recombinant antigen 85 (Ag85) proteins. The addition of interleukin 12 (IL-12) during the initial sensitization increased the magnitude of Th1 responses; however, antibody to IL-12 did not eliminate Th1 responses, suggesting that additional factors contributed to the differentiation of these cells. Finally, in the presence of IL-12, recombinant Ag85B was able to prime naive T cells for Th1 responses upon challenge with Mycobacterium-infected macrophages or Ag85B. Therefore, under the appropriate conditions, priming with whole bacteria or a subunit antigen can stimulate Mycobacterium-specific Th1 effector cell development. Further definition of the antigens and conditions required to drive naive human T cells to differentiate into Th1 effectors should facilitate the development of an improved tuberculosis vaccine.

Human deficiencies in type 1 cytokine receptors reveal the essential role of type 1 cytokines in immunity to intracellular bacteria

Studies on patients with idiopathic, severe infections due to poorly pathogenic mycobacteria and Salmonella have revealed that many of these patients are unable to produce or respond to interferon-gamma (IFN-gamma). This inability results from causative, deleterious genetic mutations in either one of four different genes in the type 1 cytokine cascade, encoding interleukin-12Rbeta1 (IL-12Rbeta1), IL-12p40, IFN-gammaR1 or IFN-gammaR2. The immunological phenotypes resulting from the seven groups of complete or partial deficiencies in type 1 cytokine (receptor) genes that have been distinguished thus far will be summarized and discussed, and placed in a broader context in relation to disease susceptibility.

Increased serum level of vascular endothelial growth factor in pulmonary tuberculosis

Pulmonary tuberculosis, one of the granulomatous diseases, has few serological markers for its activity. Recently, an increased serum level of vascular endothelial growth factor (VEGF) was detected in patients with Crohn's disease, also a granulomatous disease. We hypothesized that VEGF might be associated with the pathogenesis of pulmonary tuberculosis. We investigated the serum level of VEGF in 43 patients with active pulmonary tuberculosis, 29 patients with old tuberculosis, and 25 patients with acute bronchitis. We were able to examine the serum VEGF levels every 3 mo for a period of 6 mo in seven patients with active pulmonary tuberculosis. We examined the presence of VEGF in the resected lungs of three patients with active pulmonary tuberculosis by immunohistochemistry. The serum levels of VEGF were significantly higher in patients with active pulmonary tuberculosis than in patients with old tuberculosis and acute bronchitis. The decrease in titer of serum VEGF paralleled the clinical improvement of patients with pulmonary tuberculosis. Immunohistochemical staining of the resected lungs demonstrated the presence of VEGF in alveolar macrophages surrounding the lesion. Therefore, VEGF may be associated with the pathogenesis of pulmonary tuberculosis.

In vitro measurement of protective mycobacterial immunity: antigen-specific expansion of T cells capable of inhibiting intracellular growth of bacille Calmette-Guérin

We investigated the ability of T cells expanded with mycobacterial antigens from healthy purified protein derivative-reactive donors and bacille Calmette-Guérin (BCG)-vaccinated volunteers to inhibit intracellular growth of BCG. Peripheral blood mononuclear cells were incubated for 7 days with mycobacterial whole lysate, live BCG, tetanus toxoid as control antigen, or medium alone. Autologous monocytes were separated by plastic adherence, allowed to mature for 6 days, and infected with BCG before serving as target cells. Expanded effector cells were cocultured with target cells for 72 h. Cocultures were then treated with 0.2% saponin to lyse infected monocytes and release intracellular BCG. Quantities of viable BCG present in these lysates were studied by colony-forming unit counting and radiometric labeling. We reproducibly found that lymphocytes expanded with mycobacterial whole lysate or live BCG significantly inhibited the intracellular growth of BCG, compared with lymphocytes expanded with tetanus toxoid or rested in medium. In addition, BCG vaccination enhanced the ability of T cells to inhibit intracellular mycobacterial growth in 3 of 5 volunteers. This assay may be useful for estimates of protective immunity induced by tuberculosis vaccines in human trials.

Cellular interactions in bovine tuberculosis: release of active mycobacteria from infected macrophages by antigen-stimulated T cells

The outcome of Mycobacterium bovis infections depends on the interactions of infected macrophages with T lymphocytes. Several studies in humans and in mouse models have suggested an important role for cytotoxicity in the protective immune response to mycobacterial infections, and both CD4+ and CD8+ T cells have been shown to elicit appropriate cytolytic activity. The present study investigated in vitro interactions of T cells with M. bovis-infected macrophages in bovine tuberculosis. The results showed that following interaction with antigen-stimulated peripheral blood mononuclear cells (PBMC) from infected cattle, there was an increased presence of M. bovis in the extracellular compartment of infected macrophage cultures, as measured by incorporation of [3H]uracil into mycobacterial RNA. Furthermore, out of a panel of T-cell clones from infected cattle, it was found that a higher proportion of CD8+ clones produced an increase in the number of metabolically active extracellular M. bovis organisms compared with CD4+ clones. Finally, a positive correlation between percentage of antigen-dependent release of mycobacteria and total uracil uptake by M. bovis within culture systems was detected. This could be regarded as an indication of preferential intracellular control of mycobacteria by activated macrophages.

Development of novel tuberculosis vaccines

Efficacious control of tuberculosis (TB), one of the world's major health threats, is best achieved by a combination of chemotherapy and vaccination. The current vaccine, BCG, fails to prevent pulmonary TB in adults, which is the most prevalent form of this disease. Consequently, the design of novel vaccines against TB is urgently required. Because the acquired immune response is mediated by different T-cell sets, an optimal combination of these populations must be stimulated. As one third of the world's population is already infected with Mycobacterium tuberculosis, two types of vaccine may be required: one for eradication of already established infection and the other for prompt combat of invading microbes. A rational judgement on the efficacy of the different types of vaccine currently under development needs to await further evaluation.

A double-blind, placebo-controlled study of Mycobacterium-specific human immune responses induced by intradermal bacille Calmette-Guérin vaccination

Recent studies have indicated that type 1 T cell responses (potent interferon-gamma and cytolytic responses, with absence of interleukin-4 production) are important for protective immunity against mycobacteria. These observations suggest that assays of type 1 T cell responses may be useful as surrogate markers of protective immunity in the evaluation of new tuberculosis vaccines. To be useful as surrogate markers, immunologic assays must distinguish between vaccine recipients and control subjects in clinical trials. Previous studies have shown that bacille Calmette-Guérin (BCG) vaccination can induce human type 1 T cell responses, but randomized trials have not been done to determine whether measurement of these responses can distinguish between BCG recipients and control subjects. We have conducted a double-blind, placebo-controlled trial of intradermal vaccination with two different BCG strains. We compared the mean lymphoproliferative, cytotoxic, Th1 and Th2 cytokine, and antibody responses detected in BCG and placebo recipients. These studies demonstrated that significant increases in Mycobacterium-specific T cell proliferative responses and type 1 cytokine responses were induced by BCG when compared with results with a placebo. In addition, BCG induced significant increases in Mycobacterium-specific antibody responses with an isotype profile characteristic of a type 1 cytokine bias. T cell and antibody assays involving the use of mycobacterial whole cell lysates or live BCG were able to discriminate between BCG and placebo recipients better than were assays using mycobacterial culture filtrates. These studies provide important information for the development of immunologic assays that might be useful as surrogate markers of protective immunity in future trials of new tuberculosis vaccines.

Cytolytic T-cell responses to human dendritic cells and macrophages infected with Mycobacterium bovis BCG and recombinant BCG secreting listeriolysin

Cytolytic T-cell responses from 63 normal blood donors were monitored in a Mycobacterium bovis BCG infection system in vitro. We wanted to know whether cultured dendritic cells were capable of potentiating the cytolytic T-cell responses to M. bovis BCG. Infected cultured dendritic cells were up to ten times more effective antigen-presenting cells than macrophages in proliferative assays, while cytolytic T-cell induction did not differ significantly between dendritic cells and macrophages. Separated CD4+ and CD8+ T-cell subsets contributed equally to lysis of infected targets. Experiments comparing wild-type M. bovis BCG strain with two new recombinant M. bovis BCG strains secreting listeriolysin revealed statistically significant higher maximal lysis values for recombinant M. bovis BCG. We conclude from our in vitro infection system with mycobacteria that dendritic cells are superior to macrophages in proliferative assays but equal to macrophages in their ability to induce cytolytic T-cell responses. Moreover, our data suggest that recombinant M. bovis BCG vaccine strains secreting listeriolysin improve cytolytic T-cell responses.

Activation of Human CD8+ αβ TCR+ Cells by Mycobacterium tuberculosis Via an Alternate Class I MHC Antigen-Processing Pathway

Human immune responses to M. tuberculosis are characterized by activation of multiple T cell subsets including CD4+, CD8+, and γδ T cells, and the role of CD8+ αβ TCR+ T cells in this response is poorly understood. Stimulation of T cells from healthy tuberculin skin test-positive persons with live M. tuberculosis-H37Ra or soluble M. tuberculosis Ags readily up-regulated IL-2Rα (CD25) expression on CD8+ T cells. Purified resting and activated CD8+ T cells produced IFN-γ and proliferated to both M. tuberculosis bacilli and soluble mycobacterial Ags with monocytes as APC. Precursor frequency of mycobacterial Ag-specific CD8+ T cells by IFN-γ enzyme-linked immunospot was 5–10-fold lower than the precursor frequency of CD4+ T cells, and IFN-γ secretion by CD8+ T cells was 50–100-fold lower. CD8+ T cells secreted ∼10-fold less IFN-γ per cell than CD4+ T cells in response to mycobacterial Ags. CD8+ T cell responses to M. tuberculosis bacilli were blocked by anti-MHC class I antibody and required Ag processing. Processing of M. tuberculosis bacilli by monocytes for presentation to MHC class I-restricted CD8+ T cells was insensitive to brefeldin A treatment, which blocks the conventional MHC class I Ag-processing pathway. These results represent the first demonstration that human cells can process pathogen Ags via an alternate Ag-processing pathway for MHC class I and suggest a mechanism for participation of IFN-γ-secreting CD8+ T cells in the human immune responses to M. tuberculosis.

Interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha) are necessary in the early stages of induction of CD4 and CD8 cytotoxic T cells by Mycobacterium leprae heat shock protein (hsp) 65 kD

Cytotoxic T cells (CTL) may play an important role in host defence against mycobacterial infections. CD4 CTL are preferentially induced by mycobacteria, but both CD4 and CD8 CTL may be necessary components of a protective immune response. The 65-kD mycobacterium heat shock protein (hsp65) is a poor inducer of CTL in multibacillary leprosy (MB) patients. In this study we evaluate the possible role of cytokines in modulating the cytotoxic activity of CTL from leprosy patients and normal individuals (N) against autologous macrophages presenting Mycobacterium leprae hsp65. Our results show that hsp65-specific CTL were generated from both CD4 and CD8 lymphocytes. In N, individual cytokines as well as the combination of them were able to modify the hsp65-induced cytotoxic activity. The effect of cytokines on leprosy patients' lymphocytes was different in MB and paucibacillary (PB) patients. Thus, IL-6, IL-2, IFN-gamma or TNF-alpha did not modify the generation of hsp65-CTL from either MB (with or without an erythema nodosum episode (ENL)) or PB. In all the patients the simultaneous addition of two cytokines was required in order to increase CTL generation. In MB, IL-6 plus IFN-gamma or IL-2 increased both CD4 and CD8 CTL, while TNF-alpha plus IFN-gamma up-regulated only CD4 CTL. In PB, CD8 CTL were prominent with IL-6 plus IFN-gamma, while the increase was significant in CD4 CTL with IL-6 plus IL-2. Down-regulation of CTL was observed by addition of IL-4, IL-10, anti-IFN-gamma or anti-TNF-alpha in N controls. Our data demonstrate that IFN-gamma and TNF-alpha must be present for at least the first 60 h of the induction stage in order to generate full hsp65 CTL. Hence, IFN-gamma and TNF-alpha would be key factors in the generation of hsp65 CTL.

Immunological requirements for a subunit vaccine against tuberculosis

Tuberculosis remains one of the most important threats to world health. Current vaccination and prevention strategies are inadequate and there is an urgent need for a new vaccine. The current vaccine bacille Calmette-Guérin (BCG), is unable to protect against re-activation of disease in later life and its efficacy varies tremendously in different human populations. An ideal replacement would be a non-living subunit vaccine that could impart protective efficacy greater than BCG but without its drawbacks. Before such a goal is achieved, however, there are many parameters that need to be examined in experimental systems. Such studies have revealed that apart from the selection of immunologically relevant antigens, dosage of antigen and type of adjuvant need to be chosen carefully. These parameters need to be examined in the context of the complex biology of the disease and, despite recent progress in defining host/pathogen interactions, experimental vaccines tested so far have fallen short of the protective efficacy of BCG. A coordinated approach, stimulating the various facets of cell-mediated immunity will probably be essential for development of protective immunity through subunit vaccination.

Mycobacterium avium and purified protein derivative-specific cytotoxicity mediated by CD4+ lymphocytes from healthy HIV-seropositive and-seronegative individuals

HIV is the greatest single risk factor for the development of tuberculosis. Diseases caused by M. tuberculosis and mycobacteria are the most common opportunistic infections in HIV-infected persons, which may stem from a functional defect of the CD4+ T-cell-mediated killing of macrophages harboring mycobacteria. Our objective was to investigate the M.tuberculosis-and M. avium-specific cytotoxic capacity of T cells from healthy, bacille Calmette-Guérin-vaccinated, HIV-seropositive individuals. Blood mononuclear cells were obtained from 10 healthy HIV-seropositive and 10 healthy seronegative persons with no history of previous or active mycobacterial infection. Antigen-specific killing of macrophages presenting mycobacterial antigens (purified protein derivative or M. avium culture filtrate) was conducted. The phenotype of the killer cells was determined by a fluorescence-activated cell sorter after antigen stimulation and by using purified CD4+ and CD8+ cell subsets. Substantial, but reduced antigen-specific cytotoxicity was observed in patients with asymptomatic HIV infection. The immunological dysfunction leading to reduced cytotoxic activity in healthy HIV-seropositive subjects could not be explained by a defect in the cytotoxic capacity of the individual CD4+ lymphocyte after antigen stimulation, and it could not be explained by a reduction in the total number of CD4+ cells before antigen stimulation. The antigen-specific cytotoxic activity was, however, closely related to the ability of the CD4+ T cells to respond to mycobacterial antigens. The immunological dysfunction leading to reduced mycobacterial-specific cytotoxic activity in healthy HIV-seropositive subjects is caused either by a reduction in the number of antigen-responsive CD4+ T cells (memory) or by an impairment of their ability to respond to antigenic stimuli.

Characterization of T cells that confer a high degree of protective immunity against tuberculosis in mice after vaccination with tumor cells expressing mycobacterial hsp65

Mice vaccinated by injection with tumor cells expressing the Mycobacterium leprae gene for hsp65 acquire a remarkably high degree of protection against challenge with Mycobacterium tuberculosis. We used limiting-dilution analysis to assess the frequency of CD4+ CD8- and CD4- CD8+ splenocytes responding to mycobacterial hsp65 in such vaccinated mice. Cells of both phenotypes were present at very high and equal frequencies (approximately 1:100). Vaccination with live Mycobacterium bovis BCG also increased the frequencies of both phenotypes of hsp65-reactive cells equally (to approximately 1:2,500), whereas vaccination procedures that were not protective, with either dead BCG, hsp65 protein in incomplete Freund's adjuvant, or hsp65 mixed with tumor cells, resulted in preferential increase in CD4+ CD8- cells. Twelve CD4+ CD8- and twelve CD4- CD8+ hsp65-responsive T-cell clones were obtained and characterized. All showed conventional antigen recognition via major histocompatibility complex class II and class I pathways but differed in secretion of gamma interferon and interleukin 4 and cytotoxicity. In tests of antimycobacterial activity against M. tuberculosis, both in infected macrophages in vitro and by adoptive transfer of protection with T-cell clones injected into irradiated mice, the most effective clones were the most cytotoxic and secretion of gamma interferon made only a secondary contribution.

Stimulation of human peripheral blood mononuclear cells with live Mycobacterium bovis BCG activates cytolytic CD8+ T cells in vitro

Experimental data have shown that Mycobacterium tuberculosis can survive within the host cell and in doing so may release secreted antigen into the endogenous antigen-processing pathway. If mycobacterial antigen can gain access to MHC class I molecules then CD8+ T cells may play a role in host defence against M. tuberculosis infection. To identify whether there is a role for the CD8+ T cell in mycobacterial infection we have stimulated peripheral blood mononuclear cells (PBMC) from bacillus Calmette-Guérin (BCG) vaccinated individuals with live M. bovis BCG. The activation state of the T cells was established by staining for the interleukin-2 (IL-2) receptor (CD25), HLA-DR or the transferrin receptor (CD71). Using FACScan analysis we have shown that, in vitro, live M. bovis BCG activates significantly more CD8+ T cells in comparison to the soluble antigen purified protein derivative (PPD). In addition, live M. bovis BCG activates more CD8+ T cells than a non-viable preparation of the same M. bovis BCG following irradiation. The function of the activated CD8+ T cells was addressed using positively selected cells in a cytotoxic T-cell assay. CD8+ T cells isolated from a 7-day M. bovis BCG-stimulated PBMC culture were shown to be cytolytic against target cells infected with live M. bovis BCG, dead M. bovis BCG, and to a lesser extent, PPD. These results suggest that CD8+ T cells may be activated by stimulation with live mycobacteria, and that this subset can play a cytolytic role in the immune response to mycobacterial infections.

Cytolytic activity against mycobacterial antigens: differences between haemophiliacs with and without HIV infection

Although asymptomatic haemophiliacs have been shown to have abnormalities of their immune response, independent of HIV, clinical evidence of significant immunosuppression is limited. The only clinical report has been an outbreak of M. tuberculosis in which a group of haemophilic boys appeared unduly susceptible to infection. These boys are now all HIV seropositive. Along with a group of HIV seronegative children with coagulation disorders and non-haemophilic HIV seropositive men, these boys have been restudied to examine immune response to PPD. The HIV seropositive haemophilic boys that had had M. tuberculosis infection had reduced cytolytic response to PPD pulsed macrophages comparable to the non-haemophilic HIV seropositive men. The HIV seronegative children with coagulation disorders showed a reduction in cytolytic activity at low effector:target ratios compared to normal controls. In vitro studies showed that exogenous factor VIII concentrate could inhibit cytolytic activity to PPD pulsed macrophages. The possible role of chronic blood-borne virus infection and factor VIII concentrates in the original outbreak are discussed.

CD4+ cytolytic T cells can destroy autologous and MHC-matched macrophages but fail to kill intracellular Mycobacterium bovis-BCG

Mycobacterium bovis-BCG infected macrophages were exposed in vitro to PPD-stimulated T lymphocytes from tuberculin responsive donors or to a panel of mycobacterial-antigen specific CD4+ T cell clones. Both polyclonal and clonal T cells caused considerable antigen-specific lysis of autologous or MHC class II matched macrophages. However, lysis of infected macrophages did not significantly affect the number of viable mycobacteria which were released into the culture media from lysed macrophages. In tuberculosis, CD4+ cytolytic T cells may be primarily involved in tissue destruction and lack a significant role in acquired cellular immunity.

Lysis of human macrophages by cytolytic CD4+ T cells fails to affect survival of intracellular Mycobacterium bovis-bacille Calmette-Guérin (BCG)

Human CD4+, mycobacteria-specific, cytolytic T cell clones were used to lyse BCG-infected macrophages, and the effect on the subsequent growth and viability of the organisms was examined. The survival of released bacteria following cell lysis was assessed by both 3H-uridine labelling and colony-forming unit (CFU) estimation. The results indicate that even when effective antigen-specific or lectin-mediated cytolysis of the infected macrophages was achieved, there was no evidence for a direct mycobactericidal effect on the intracellular bacteria. This remained the case even if the period of co-culture of T cells and macrophages was extended up to 48 h. Pretreatment of the macrophages with interferon-gamma (IFN-gamma) was not able to act together with T cell-mediated lysis to produce inhibition of mycobacterial growth.

Lack of cytotoxic activity against Mycobacterium leprae 65-kD heat shock protein (hsp) in multibacillary leprosy patients

Cytotoxic T cells play an important role in host defence mechanisms, as well as in the immunopathology of leprosy. In this study, we evaluated whether Mycobacterium leprae hsp18, hsp65 and Myco. tuberculosis hsp71 could induce cytotoxic T cell activity against autologous macrophages pulsed with these hsp. Paucibacillary (PB) patients and normal controls generated more effector cells than multibacillary (MB) patients with all three hsp tested. There was no cross-reactivity between any of the hsp tested. Mycobacterium leprae hsp65 induced cytotoxic responses only in those MB patients undergoing an erythema nodosum leprosum (ENL) episode. Although hsp65 and hsp18 induced similar proliferation in MB patients, a high proportion of these patients did not generate cytotoxic effector cells in response to hsp65. Hence, those T cells reacting to hsp65 may play an important role in the control of Myco. leprae infection.

Immune responsiveness and lymphokine production in patients with tuberculosis and healthy controls

The aim of the present study was to determine the profile of immune responsiveness that differentiates patients with tuberculosis (TB) from healthy tuberculin-positive controls. Forty-five patients with pulmonary TB and 16 healthy tuberculin-positive controls, all human immunodeficiency virus negative, were studied. Patients had decreased reactivity to tuberculin, diminished proliferative response to purified protein derivative (PPD), lower concentrations of interleukin-2 (IL-2) and gamma interferon in PPD-stimulated cultures, no increase in the percentage of gamma/delta cells in PPD-stimulated cultures, and higher immunoglobulin G antimycobacterial antibodies compared with control subjects. Furthermore, controls exhibited decreased production of IL-4 by PPD-stimulated cells. Multivariate discriminant and factor analyses demonstrated divergent patterns of immune reactivity against mycobacterial antigens. The association of IL-4 and immunoglobulin G antibody levels in patients, in contrast to the high reactivity to tuberculin, increased proliferation to PPD, and higher levels of IL-2 and gamma interferon observed in healthy controls suggested that most TB patients exhibit a TH2 pattern of immune responsiveness while tuberculin-positive healthy individuals have a TH1 pattern.

Towards a DNA vaccine against tuberculosis

Expression of the gene for a single mycobacterial antigen (Mycobacterium leprae hsp65) in adult Balb/c mice resulted in substantial cell-mediated protection against challenge with M. tuberculosis. CD4 and CD8 T cells cloned from spleens of such immunized mice passively transferred protection to non-immunized mice, and CD8 cells selectively lysed macrophages infected with M. tuberculosis. Three modes of expressing the gene have been tested: (1) expression from a retroviral vector (pZIPNeoSV) in implanted J774 tumour cells, (2) expression from the same vector via bone marrow cells transfected in vitro and used to reconstitute irradiated mice, and (3) in a preliminary experiment, from CMV immediate-early and hydroxymethylglutaryl Co-A reductase promoters injected as plasmid DNA into muscle.

Protection against tuberculosis by passive transfer with T-cell clones recognizing mycobacterial heat-shock protein 65

We have previously shown that mice vaccinated by injection with J774 macrophage-like tumour cells that expressed Mycobacterium leprae heat-shock protein (hsp) 65 as a transgene had acquired a remarkably high degree of protection against subsequent challenge with virulent M. tuberculosis. We show here that antigen-specific T cells cloned from spleens of such vaccinated animals can transfer a high level of protection to non-vaccinated recipients. The most efficient cells were of T-cell receptor (TCR) alpha beta+ and CD4- CD8+ type and specifically lysed mycobacteria-infected macrophages. These findings are consistent with the importance for protective immunity of engaging the endogenous antigen-presenting pathway to bias the immune response towards a cytolytic action against a mycobacterial antigen that is expressed at the surface of infected macrophages. TCR gamma delta+ and TCR alpha beta+ cells interacted synergistically.

Reduced NK activity correlates with active disease in HIV- patients with multidrug-resistant pulmonary tuberculosis

There has been a global increase in the incidence of multidrug-resistant pulmonary tuberculosis (TB). As there are no previous reports of immune function in HIV- patients with multidrug-resistant pulmonary TB, a comprehensive assessment of cellular immunity in this setting was undertaken. This involved a prospective, case-controlled study which included five patients with active multidrug-resistant pulmonary TB and five matched controls with active non-resistant infection, and documented the changes in immune parameters which occurred upon clinical resolution. Patients with multidrug-resistant TB had significantly lower fresh natural killer (NK) cell activity than matched controls with non-resistant pulmonary TB (P < 0.05). This was a specific abnormality, as there were no significant differences in antigen-specific cytotoxicity or lymphocyte proliferation in the case-controlled study. Follow-up assessment of the patients with multidrug-resistant infections indicated that clinical improvement correlated with a moderate increase in NK cell activity. Impaired NK cell function may be involved in the pathogenesis of multidrug-resistant TB.

The effect of prostaglandin E2 and indomethacin on the cytotoxic response to mycobacterial antigens

The effect of prostaglandin E2 and indomethacin on the generation of cytotoxic T-lymphocytes in response to Mycobacterium tuberculosis (MTB) antigens was compared between healthy controls and rheumatoid arthritis patients. Peripheral blood mononuclear cells (PBMC) from 16 healthy individuals and 15 RA patients were stimulated for 7 days with an irradiated, sonicated preparation of MTB in the presence or absence of PGE2 or indomethacin and assayed for cytotoxic activity on autologous target cells prepulsed with MTB. The mean cytotoxic activity generated was lower in patients than in controls. Exogenous PGE2 suppressed the cytotoxicity directed against MTB pulsed targets in 12 of 16 controls, but in only 1 of 11 patients. Indomethacin enhanced this cytotoxicity in only 2 of 16 controls but in 6 of 10 RA patients. When effector cells were derived from the synovial fluid, PGE2 again had no effect and indomethacin enhanced the cytotoxicity. Our data suggest that the depressed cytotoxic response of RA patients to MTB may be due to the production of endogenous PGE2. Cyclooxygenase inhibitors commonly used in the treatment of RA may influence MTB induced cytotoxicity in patients. In addition to their anti-inflammatory effects within the joint, non-steroidal anti-inflammatory drugs may potentially enhance cytotoxic reactions which are induced by antigens, such as MTB cross-reactive heat shock proteins.

Detection of Salmonella-specific L3T4+ and Lyt-2+ T cells which can proliferate in vitro and mediate delayed-type hypersensitivity reactivity

This study was based on an initial observation that, although culture of T cells from Salmonella-infected mice with concanavalin A induced both L3T4+ T cells and Lyt-2+ T cells to proliferate, there was a relative increase in the responsiveness of the Lyt-2+ T cells in suspensions harvested from mice with secondary infection. Accordingly, primed T cells, obtained from the peritoneal cavities and spleens of mice that had received one or two intraperitoneal doses of Salmonella were examined for the presence of antigen-specific, class I major histocompatibility complex (MHC)-restricted Lyt-2+ T cells. After primary infection with avirulent Salmonella enteritidis 11RX (11RX) only L3T4+ T cells could be induced to proliferate in response to formalin-killed 11RX organisms, and a second dose of live 11RX did not change the phenotype of the responding T-cell population. In contrast, secondary challenge with S. typhimurium C5 (C5) generated cell populations where both L3T4+ and Lyt-2+ T cells proliferated when cultured with formalin-killed 11RX. Transfer of delayed-type hypersensitivity (DTH) using mixtures of primed T cells and either killed or live Salmonella organisms demonstrated that DTH was mediated by L3T4+ T cells, and secondary infection with either the 11RX or C5 strain did not change this result. However, antigen-specific Lyt-2+ T cells which mediated DTH reactivity were detected using a Salmonella-infected cell line which expressed MHC-coded class I but not class II products. These Lyt-2+ T cells were present in the spleen and peritoneal cavity after secondary infection and in the peritoneal cavity late after a primary infection with 11RX.

IFN-gamma, IL-6 and IL-4 modulate M. leprae- or PPD-specific cytotoxic T cells in leprosy patients

Specific cytotoxic T cells against intracellular pathogens may be generated in vitro. On the other hand it is well known that cytokines can regulate almost every aspect of immune function. The aim of this study was to evaluate the effect of some cytokines on the generation of cytotoxic T cells with specificity for Mycobacterium leprae- or PPD-pulsed autologous macrophages from leprosy patients and normal controls. Peripheral blood mononuclear cells from M. bovis BCG-immunized controls or from leprosy patients were stimulated with antigen, in the presence or absence of cytokines, for 7 days. These were used as effector cells in a 4-h [51Cr]-release assay. Our results show that development of cytotoxic T cells may be enhanced by gamma-IFN, IL-6 or the combination of IL-6 and IL-2. Addition of IL-2 or TNF-alpha alone did not modify the generation of cytotoxic activity. IL-4 down-regulated the cytotoxic response and gamma-IFN was able to counteract this effect. Hence, the generation of specific cytotoxic T cells can be modulated by cytokines. Whether this cytotoxic mechanism contributes to protection or tissue damage in M. leprae infection remains to be determined.

Antigen-presenting cell types

Different antigen-presenting cells elicit responses in different T-cell populations for primary activation, secondary stimulation and cytotoxic effector functions. Maturing bone marrow derived dendritic cells may acquire and process antigens, transport them to lymph nodes and activate naive T cells located there. By contrast, follicular dendritic cells, acquiring antigen-antibody complexes, maintain 'memory' via B-cell activation. Effector memory T cells recognize various tissue cells bearing antigen and we speculate that they may also target specialized antigen-presenting dendritic populations.

Tuberculosis--immunopathogenesis and therapy

Infection with Mycobacterium tuberculosis (TB) has returned to the forefront of public and medical concern because of the recent sharp increase in the number of cases. Major strides have been made in understanding the pathogenesis of TB, and some of these basic advances are being applied clinically. This review focuses on current concepts of the host response to TB, the changing epidemiology of TB, and optimal treatment strategies.

Reduced natural killer cell activity in multi-drug resistant pulmonary tuberculosis

Cellular immune status in five patients with multi-drug resistant pulmonary tuberculosis was investigated and compared with five matched controls with non-resistant tuberculosis. A significant reduction in fresh natural killer (NK)-cell activity was found in the resistant group (P less than 0.005). There were no significant differences between the two groups in lymphocyte phenotype, proliferation or PPD-specific cytotoxicity. Reduced NK-cell function may play a role in the pathogenesis of multi-drug resistant pulmonary tuberculosis.