Circulating, Mycobacterium tuberculosis-specific lymphocytes from PPD skin test-negative patients with tuberculosis do not secrete interferon-gamma (IFN-gamma) and lack the cutaneous lymphocyte antigen skin-selective homing receptor

In vitro analysis of antigen induced T cell-monocyte conjugates by imaging flow cytometry

There is a lack of suitable correlates of immune protection against Mycobacterium tuberculosis (Mtb) infection. T cells and monocytes play key roles in host immunity against Mtb. Thus, a method that allows assessing their interaction would contribute to the understanding of immune regulation in tuberculosis (TB). We have established imaging flow cytometer (IFC) based in vitro assay for the analysis of early events in T cell-monocyte interaction, upstream of cytokine production and T cell proliferation. This was achieved through short term stimulation of peripheral blood mononuclear cells (PBMC) from healthy Norwegian blood donors with Mycobacterium bovis Bacille Calmette-Guérin (BCG). In our assay, we examined the kinetics of BCG uptake by monocytes using fluorescently labeled BCG and T cell-monocyte interaction based on synapse formation (CD3/TCR polarization). Our results showed that BCG stimulation induced a gradual increase in the proportion of conjugated T cells displaying NF-κB translocation to the nucleus in a time dependent manner, with the highest frequency observed at 6 h. We subsequently tested PBMC from a small cohort of active TB patients (n = 7) and observed a similar BCG induced NF-κB translocation in T cells conjugated with monocytes. The method allowed for simultaneous evaluation of T cell-monocyte conjugates and T cell activation as measured by NF-κB translocation, following short-term challenge of human PBMC with BCG. Whether this novel approach could serve as a diagnostic or prognostic marker needs to be investigated using a wide array of Mtb specific antigens in a larger cohort of patients with different TB infection status.

Influenza, but not HIV-specific CTL epitopes, elicits delayed-type hypersensitivity (DTH) reactions in HIV-infected patients

The induction of cytotoxic T lymphocytes (CTLs) is believed to be an important defense mechanism against viral infections. The availability of simple, sensitive, specific and physiologically informative in vivo tests, applicable to humans, would greatly elucidate the nature of protective immune responses and facilitate immune monitoring in large vaccine trials. Here we studied the possibility of using defined HLA-A*02:01-restricted CTL epitopes from influenza matrix protein (GL9, GILGFVFTL) and HIV Gag p17 (SL9, SLYNTVATL) to elicit a cutaneous delayed-type hypersensitivity (DTH) reaction. Our results show that the GL9 but not the SL9 epitope was able to induce a DTH reaction. HIV infection status, HIV RNA level and CD4(+) T-cell counts were not predictive of the extent of DTH reactions. However, a markedly reduced expression of skin homing markers CD103 and cutaneous lymphocyte associated Ag (CLA) on epitope-specific CTL populations was associated with a lack of SL9 DTH reactivity. These data demonstrate that DTH reactions can be elicited by optimally defined CTL epitopes per se and point towards specific homing markers that are required for such reactions. These data may offer new insights into the immune pathogenesis of HIV infection and provide the basis of novel immune monitoring approaches for large-scale HIV vaccine trials.

Regulation of human T-cell homing receptor expression in cutaneous bacterial infection

We investigated the regulation of T-cell homing receptors in infectious disease by evaluating the cutaneous lymphocyte antigen (CLA) in human leprosy. We found that CLA-positive cells were enriched in the infectious lesions associated with restricting the growth of the pathogen Mycobacterium leprae, as assessed by the clinical course of infection. Moreover, CLA expression on T cells isolated from the peripheral blood of antigen-responsive tuberculoid leprosy patients increased in the presence of M. leprae (2.4-fold median increase; range 0.8-6.1, n = 17), but not in unresponsive lepromatous leprosy patients (1.0-fold median increase; range 0.1-2.2, n = 10; P < 0.005). Mycobacterium leprae specifically up-regulated the skin homing receptor, CLA, but not alpha(4)/beta(7), the intestinal homing receptor, which decreased on T cells of patients with tuberculoid leprosy after antigen stimulation (2.2-fold median decrease; range 1.6-3.4, n = 3). Our data indicate that CLA expression is regulated during the course of leprosy infection and suggest that T-cell responsiveness to a microbial antigen directs antigen-specific T cells to the site of infection.

The level of PPD-specific IFN-γ-producing CD4+ T cells in the blood predicts the in vivo response to PPD

There are no reliable means for detecting subclinical mycobacterial infections. The recent sequencing of several mycobacterial genomes has now afforded new opportunities for the development of pathogen-specific diagnostic tests, critical in the context of leprosy and tuberculosis control. In the present study, we applied a multi-parametric flow cytometric analysis that allowed the investigation of T-cell functions in order to define immunological markers that measure previous exposure to mycobacteria. We compared the in vivo response to PPD, the gold standard skin test reagent for measuring previous exposure to Mycobacterium tuberculosis, with in vitro parameters of leukocyte activation in five PPD positive and five PPD negative healthy volunteers. PPD-stimulated peripheral leukocytes expressing CD4, CD69, cutaneous lymphocyte-associated antigen (CLA) and intracellular IFN-gamma were enumerated in whole blood and compared with the size of in vivo PPD-induced induration and IFN-gamma production levels as measured by ELISA in supernatants of PPD-stimulated peripheral blood mononuclear cells. The reactivity to the tuberculin skin test (TST) was associated with markedly increased frequencies of PPD-responsive activated (CD69+) and IFN-gamma-producing CD4+T cells. Detection of PPD-specific IFN-gamma producing leukocytes was restricted to CD4+T cells and a subset of these cells was shown to express the skin homing molecule CLA. Multiple linear regression modeling of responses to PPD showed the highest association between skin test indurations and frequencies of PPD-responsive IFN-gamma-producing CD4+CD69+ T cells. Our data show that the in vitro enumeration of antigen-specific IFN-gamma-producing CD4+ T cells can provide an alternative to the in vivo tuberculin test for the detection of latent Mycobacterium tuberculosis infection. Moreover, the measurement of these immunological parameters can be useful for the screening of new specific antigens defined by the genome sequence allowing selection of the best candidates for new diagnostics (including new skin tests), and vaccines for leprosy and tuberculosis.

Cytokine Profile of T lymphocytes from Peripheral Blood and Bronchoalveolar Lavage Fluid in Patients with Active Pulmonary Tuberculosis

The possible immunological relationship between the pattern of Th1/Th2 cytokine production and tuberculin reactivity was assessed in patients with active Mycobacterium tuberculosis infection. The production of the intracellular cytokines interferon (IFN)-gamma and interleukin-4 (IL-4) was measured in CD4(+) and CD8(+) T cells obtained from peripheral blood and bronchoalveolar lavage fluid (BALF) of 20 tuberculin skin-positive patients and compared with the findings recorded in nine tuberculin skin-negative patients with active pulmonary tuberculosis. Upon stimulation with phorbol 12-myristate acetate/ionomycin for 6 h, tuberculin-negative patients had a significantly higher proportion of IFN-gamma-producing CD4(+) T lymphocytes in BALF than in peripheral blood, while both CD4(+) and CD8(+) T-lymphocyte subsets in BALF of tuberculin-positive patients secreted more IFN-gamma than their peripheral blood counterparts. Tuberculin-negative patients had a significantly higher proportion of IFN-gamma-producing CD4(+) T lymphocytes in peripheral blood than tuberculin-positive patients. There was no significant difference in the production of IFN-gamma by BALF CD4(+) T lymphocytes, or by either peripheral blood or BALF CD8(+) T lymphocytes. In two tuberculin-negative patients, peripheral blood CD4(+) T lymphocytes produced IL-4. Study results suggested a higher immune activity in the blood of tuberculin-negative patients, with an increased lymphocyte activity in BALF versus peripheral blood in both patient groups.

Detection by Flow Cytometry of ESAT-6- and PPD-Specific Circulating CD4+ T Lymphocytes as a Diagnostic Tool for Tuberculosis

BACKGROUND

The identification of mycobacteria represents the gold standard in the diagnosis of tuberculosis (TB), but it is not applicable in all patients, and immunological tests, such as the tuberculin skin test (TST), are not specific and sensitive enough.

METHODS

By flow cytometry, we measured the CD4 T-cell response to purified protein derivative (PPD) and early secretory antigenic target-6 (ESAT-6) protein using the intracellular cytokine staining technique on whole blood samples obtained from active TB (n = 16), latent TB (n = 17), Bacille Calmette-Guérin (BCG)-vaccinated (n = 11) and healthy (n = 10) donors. All the patients were also tested with conventional TST.

RESULTS

The identification by flow cytometry of PPD-specific T lymphocytes upon antigen stimulation of whole blood enables the discrimination of active TB, latent TB and BCG-vaccinated subjects from healthy individuals, whereas the ESAT-6 response discriminated active TB from healthy and BCG-vaccinated individuals. Moreover, this test enables identification of active TB patients who were negative on TST and to distinguish between TB and non-typical mycobacteria TB infections.

CONCLUSIONS

The identification by flow cytometry of antigen-specific T lymphocytes upon antigen stimulation of whole blood has a better positive predictive value than TST, and could represent a further tool in the diagnosis of TB infection.

Comparative and prospective study of different immune parameters in healthy subjects at risk for tuberculosis and in tuberculosis patients

It has not been fully elucidated which of the components of the immune response against Mycobacterium tuberculosis is indicative of resistance or susceptibility. The aim of this study was to identify an immune parameter that could be indicative of either resistance or susceptibility to M. tuberculosis infection. We prospectively studied (three determinations, at months 0, 8, and 12) 15 patients with chronic pulmonary tuberculosis and 42 healthy individuals with a recent and frequent contact with tuberculosis patients. Peripheral blood mononuclear cells were stimulated with a whole-protein extract or the 30-kDa antigen of M. tuberculosis for 6 days, and several immune parameters were determined. No consistent differences between tuberculosis patients and healthy controls were detected in most immune parameters studied, including the expression of different activation antigens, cytokine secretion, lymphocyte proliferation, and nitric oxide production. However, the synthesis of tumor necrosis factor alpha, the intracellular detection of gamma interferon, and the apoptosis of monocytes under certain culture conditions tended to show clear-cut differences in cells from patients and controls (P < 0.05 in all cases for most determinations). Nevertheless, when results were analyzed on an individual basis, it was evident that a significant degree of overlapping of values from patients and controls occurred for all parameters studied. We conclude that although the immune parameters tested do not allow the identification of individuals susceptible to M. tuberculosis, the specificity and sensitivity of some of them could be improved through future studies.

Mycobacterium bovis infection and tuberculosis in cattle

This review considers the possible events that can occur when cattle are exposed to Mycobacterium bovis and, where appropriate, draws on principles accepted for tuberculosis infection in humans and laboratory animal models. Consideration is given to the many complex factors which influence the outcome of challenge with tubercle bacilli. These include features inherent to the mycobacterium, the host and the environment. It is apparent that clinical disease probably occurs only in a relatively small, but undetermined, proportion of cattle that are exposed to Al. bovis. The majority of animals may clear infection or control the bacilli, possibly in a condition of latency. It is concluded that a better understanding of the dynamics of the events following M. bovis exposure and subsequent infection in cattle would be of significant benefit in developing new tools appropriate for disease control and to designing optimal approaches for their application.