THE IMMUNOLOGY OF TUBERCULOSIS

Mechanisms of Granulomatous Lung Disease from Inhaled Beryllium: The Role of Antigenicity in Granuloma Formation

Granulomatous lung disease is a debilitating and sometimes fatal condition encountered in humans, for which the cellular and molecular mechanisms are poorly understood. Two patterns of granulomatous lung disease are recognized; foreign-body reactions and immune-mediated granulomas. Beryllium inhalation by humans results, in a small number of exposed individuals, in a chronic, granulomatous, immune-mediated pulmonary disease (chronic beryllium lung disease, CBD). Animal models used to study CBD have demonstrated significant species differences in the pathologic response to beryllium. While rats exposed to beryllium appear to develop a chronic, foreign-body response within the lung, dogs so exposed develop beryllium-specific immune responses within the lung and blood, accompanied by immune granulomas within the lung. At the heart of this difference appears to be the ability of the dog, but not the rat, to immunologically recognize the antigenicity of beryllium. This important difference further underscores the need to understand the mechanistic differences among similar disease syndromes, particularly if therapeutic regimens are to be used.

Safety of ESAT-6

A recombinant dimer of the Mycobacterium tuberculosis (MTb) 6 kDa early secreted antigenic target (ESAT-6) was produced in Lactococcus lactis. Pharmacodynamic and safety studies were carried out in guinea pigs, rats, mice and dogs with intradermal (id), subcutaneous (sc) and intravenous (iv) administration of the antigen. In contrast to tuberculin purified protein derivative (PPD) the recombinant dimer (rdESAT-6) was able to discriminate MTb infection from BCG vaccination in vivo. In guinea pigs sensitized by infection with MTb, 1 microg rdESAT-6 gave a mean delayed-type hypersensitivity (DTH) response of 22 mm, a significantly stronger reaction than in animals sensitised by the environmental mycobacteria M. kansasii, M. szulgai and M. marinum. rdESAT-6 proved to be a safe tuberculin reagent in a dose range of 1-1000 microg with no or only minor local reactions.

CD69 expression on CD4+ T lymphocytes after in vitro stimulation with tuberculin is an indicator of immune sensitization against Mycobacterium tuberculosis antigens

The expression of the CD69 antigen on CD4 T lymphocytes after in vitro stimulation with purified protein derivative (2 tuberculin units) was used to evaluate the tuberculin reactivities of 52 individuals from four experimental groups: Mycobacterium bovis BCG-vaccinated healthy individuals with a negative tuberculin skin test (TST) result (group A), BCG-vaccinated healthy individuals with a positive TST result (group B), patients with active tuberculosis (TB) before treatment (group C), and individuals with clinically inactive TB who had previously completed a prescribed course of chemotherapy (group D). The expression of CD69 on CD4 T lymphocytes was significantly higher in patients with active TB (16.2%+/-7.3%), individuals with clinically inactive TB (10.5%+/-7.4%), and healthy individuals with a positive TST result (15.5%+/-7.2%) than in healthy individuals with a negative TST result (3.8%+/-4.3%) (P<0.005). We confirmed the correlation between CD69 antigen expression on T lymphocytes after stimulation with tuberculin and the TST induration diameter (Spearman rho=0.783; P<0.001), an assay for gamma interferon (the Quantiferon-TB assay; Spearman rho=0.613; P<0.001), and the lymphocyte BLAST transformation test (Spearman rho=0.537; P<0.001). Our results demonstrate the usefulness of the determination of CD69 on CD4 T lymphocytes after in vitro stimulation with tuberculin as a rapid indicator of immune sensitization against Mycobacterium tuberculosis.

Mycobacterium tuberculosis genome-wide screen exposes multiple CD8 T cell epitopes

Mounting evidence suggests human leucocyte antigen (HLA) class I-restricted CD8(+) T cells play a role in protective immunity against tuberculosis yet relatively few epitopes specific for the causative organism, Mycobacterium tuberculosis, are reported. Here a total genome-wide screen of M. tuberculosis was used to identify putative HLA-B*3501 T cell epitopes. Of 479 predicted epitopes, 13 with the highest score were synthesized and used to restimulate lymphocytes from naturally exposed HLA-B*3501 healthy individuals in cultured and ex vivo enzyme-linked immunospot (ELISPOT) assays for interferon (IFN)-gamma. All 13 peptides elicited a response that varied considerably between individuals. For three peptides CD8(+) T cell lines were expanded and four of the 13 were recognized permissively through the HLA-B7 supertype family. Although further testing is required we show the genome-wide screen to be feasible for the identification of unknown mycobacterial antigens involved in immunity against natural infection. While the mechanisms of protective immunity against M. tuberculosis infection remain unclear, conventional class I-restricted CD8(+) T cell responses appear to be widespread throughout the genome.

Evolution and current use of the tuberculin test

Since it was first introduced in the late 1800s, the tuberculin test has undergone continual refinement in its formulation, standardization, and dosage, as well as its interpretation and indications for use. New guidelines have replaced universal screening with targeted testing and rigid definitions of positivity with individualized criteria formulated from a Bayesian approach. This review summarizes the evolution of the test and provides information to help gauge its predictive value.

Cell-mediated immune response to tuberculosis antigens: comparison of skin testing and measurement of in vitro gamma interferon production in whole-blood culture

Although delayed-type hypersensitivity skin testing with tuberculin purified protein derivative (PPD) is the standard for tuberculosis screening, its variability suggests the need for a more sensitive, noninvasive test. An in vitro whole-blood assay has been proposed as an alternative. Using health care worker volunteers, we confirmed the correlation between PPD skin test (PPD-ST) results (positive, induration of >15 mm) and a standardized gamma interferon (IFN-gamma) assay, QuantiFERON-TB (Q-IFN), manufactured by CSL Biosciences in Australia, and we evaluated Mycobacterium tuberculosis culture subfractions as potential substitutes for PPD. Twenty healthy volunteers with positive PPD-ST results and 20 PPD-ST-negative controls were enrolled. Whole blood was cultured with human PPD antigens (HuPPD), Mycobacterium avium complex (MAC) PPD, phytohemagglutinin (PHA), and four M. tuberculosis culture subfractions: low-molecular-weight culture, filtrate, culture filtrate without lipoarabinomannan, soluble cell wall proteins, and cytosolic proteins, all developed from M. tuberculosis strain H(37)RV. Secretion of IFN-gamma (expressed as international units per milliliter) was measured by an enzyme immunoassay. The PPD or subculture fraction response as a percentage of the PHA response was used to determine positivity. Sixteen of 20 PPD-ST-positive individuals were classified as M. tuberculosis positive by Q-IFN, and 1 was classified as MAC positive. Sixteen of 20 PPD-ST-negative individuals were M. tuberculosis negative by Q-IFN, 2 were MAC positive, and 2 were M. tuberculosis positive. The tuberculosis culture subfractions stimulated IFN-gamma production in PPD-ST-positive volunteers, and significant differences could be seen between the two PPD-ST groups with all subfractions except soluble cell wall protein; however, the response was variable and no better than the Q-IFN PPD. The agreement between the Q-IFN test and the PPD-ST was good (Cohen's kappa = 0.73). The Q-IFN assay can be a useful tool in further studies of immune responses to M. tuberculosis antigens.

Comparative cutaneous testing with purified protein derivative and the antigen complex A60 in vaccinated subjects and tuberculosis patients

Some 840 bacille Calmette-Guérin (BCG)-vaccinated healthy controls and tuberculosis patients from two Chinese hospitals were submitted to comparative skin tests with purified protein derivative of tuberculin (PPD; as reference) and with the antigen complex A60 from Mycobacterium bovis BCG. In a first trial, including 581 persons (185 healthy juveniles, 180 healthy adults and 216 tuberculosis patients), a limited dose of A60 (1 microgram) was used. Performance of the A60 test was similar to that of 5 I.U. PPD for controls (cut-off values = 5 mm induration diameter), but lower than that seen for tuberculosis patients (10 mm cut-off values). A second survey was conducted on 259 persons (109 recently revaccinated healthy persons, considered as tuberculin-negative in the first trial, and 150 tuberculosis patients), using a higher dose of A60 (2 micrograms) and the same dose of PPD (5 I.U.). Similar results were obtained with the two tests in all cases, thus supporting the possibility of PPD replacement by A60 in cutaneous testing. The pattern of induration diameter distribution in healthy subjects who took part in the first testing round (64% positively rate) was displaced to the inactivity side (with a peak at 5 to 9-mm diameter), in comparison with the second round (90% positivity rate and peak at 10-14 mm). This indicates a progressive fading of cellular immunity reactions after BCG vaccination. In tuberculosis patients, no correlation was found among the following three parameters: positivity at cutaneous testing (with PPD or A60), titer of anti-A60 mycobacterial immunoglobulins in blood (IgG titer higher than cut-off line) and presence of mycobacteria in sputum.

Immunology of tuberculosis

TB is a chronic, necrotizing infection caused by M. tuberculosis. The clinical manifestations of disease are the result of a balance between the host response and bacterial virulence. Cellular immunity is responsible for effective control of infection, but cytokines released during the process of cellular immunity may also cause harm to the host. Humoral immunity plays little part in protection against TB. Individuals with defective cellular immunity are much more susceptible to disease from M. tuberculosis and are more likely to have a disseminated form of TB.

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.

Use of the SL-IV and the PGL-Tb1 glycolipid antigens in ELISA for the diagnosis of tuberculosis in AIDS patients

At a predetermined specificity of 100.0%, the sensitivity of ELISA using the PGL-Tb1 and SL-IV antigens and IgG assays was 35.0% for the diagnosis of tuberculosis in AIDS patients (44.1% when tuberculosis was diagnosed before AIDS, 21.7% when AIDS was diagnosed before tuberculosis). Serial assays in sera collected from 11 AIDS patients before tuberculosis was diagnosed indicated that significant antibody titres were detected 10 months before the onset of clinical tuberculosis. Consequently, it was proposed that serodiagnosis using the glycolipid specific antigens should help in deciding on preventive antituberculosis treatment in these patients.

Evaluación de las subpoblaciones de linfocitos T en pacientes tuberculosos empleand la modulación con teofilina

Se evaluaron las poblaciones y subpoblaciones linfocitarias en pacientes con tuberculosis pulmonar antes y durante la terapia relacionando estos valores con la incidencia y evolución de la enfermedad. Pacientes en sus diversas manifestaciones clínicas, vírgenes de tratamiento, se estudiaron por baciloscopía (BAAR), radiología, i.d.r. Mantoux y análisis complementarios. Se cuantificaron mediante la prueba de Rosetas espontáneas (RE) linfocitos T totales y activos (RE a 4ºC y 37ºC), T colaboradores (RE Teofilina Resistentes: RETR) y supresores (RE Teofilina Sensibles: RETS). Los exámenes se repitieron en los mismos sujetos iniciado el tratamiento y en testigos sanos (TS). Se demostró en los pacientes en todas sus formas clínicas un descenso significativo en los valores relativos y absolutos de células T y en la relación RETR/RETS (menor de 1). Existe asociación entre la forma clínica y el número de linfocitos T colaboradores. Los pacientes en tratamiento con evolución favorable, evidenciaron un incremento significativo en los linfocitos T totales, activos, colaboradores y en la relación RETR/RETS. Los enfermos con baciloscopía altamente positiva presentaron i.d.r. Mantoux baja o negativa y marcado descenso de células inmunocompetentes. Se comprobó asociación entre estas tres variables, lo mismo que entre el estado nutricional y la predisposición a contraer la enfermedad.

Evaluation of lipoarabinomannan for the serological diagnosis of tuberculosis

The availability of highly purified lipoarabinomannan from Mycobacterium tuberculosis in its native acylated, highly antigenic state allowed its application to the serodiagnosis of tuberculosis in patients from the Republic of Mexico. Antilipoarabinomannan immunoglobulin G antibodies in sera from 66 patients with pulmonary, miliary, and pleural tuberculosis and tuberculosis lymphadenities were measured by using the enzyme-linked immunosorbent assay against sera from a control population of healthy individuals, people with histoplasmosis, and people with lung diseases not caused by mycobacteria. The results pointed to an unexpectedly high degree of specificity of 91% and a sensitivity of 72%, comparable to figures from previous studies with other purified antigens; most of the false-positive results were for patients with histoplasmosis. Thus, lipoarabinomannan of M. tuberculosis is a potentially useful antigen for the serodiagnosis of tuberculosis.

Evaluation of a novel 2,3-diacyl-trehalose-2'-sulphate (SL-IV) antigen for case finding and diagnosis of leprosy and tuberculosis

Serum IgG and IgM antibodies against a 2,3-diacyl-trehalose-2'-sulphate (SL-IV) antigen using ELISA were determined in controls (n = 288) and in leprosy (n = 210) and tuberculosis (n = 99) patients. In all assays, the amount of antigen per well was 100.0 ng and sera were diluted 1/250. In the case of leprosy, anti-SL-IV IgG and IgM antibody titres increased from the tuberculoid towards the lepromatous pole of the spectrum. In the tested population, the sensitivity of the assay was 93.2% in multibacillary leprosy and 33.3% in paucibacillary leprosy (specificity of 88.7%). Multibacillary patients with erythema nodosum leprosum (ENL) had lower titres than non-ENL. ELISA results were similar to those obtained using the Mycobacterium leprae phenolic glycolipid-I (PGL-I) antigen. In the case of tuberculosis (pulmonary and extrapulmonary), significant titres of anti SL-IV IgG and IgM antibodies were detected in about 75% of the patients using a cutoff point of 0.150, and in 51.6% using a cutoff of 0.300 (specificities were, respectively, 88% and 100%). We concluded that the determination of IgG and IgM antibodies against SL-IV was useful in leprosy and tuberculosis case finding program using a cutoff point of 0.150, and for serodiagnosis using a cutoff of 0.300.

Serological analysis of human tuberculosis by an ELISA with mycobacterial antigen 60

An ELISA method for detecting serum antibodies against A60, an antigen prepared from the cytoplasm of Mycobacterium bovis BCG, has been applied to 385 subjects, namely 197 controls (neonates, healthy adults, and tuberculin negative, nontuberculous patients), and 188 subjects at various stages of tuberculous infection and disease. Most IgM determinations gave negative results. While the neonates and normal adults had titers of IgG anti-A60 antibodies below the cut off value, wide variations in antibody titers were observed among the various types of subjects infected by M. tuberculosis. The results obtained with nontuberculous subjects were: 100% negative IgG in neonates and healthy adult individuals and 6.4% "false positive" cases among 124 non-tuberculous patients. The percentage of serologically positive cases of tuberculosis was: 5.9% in latent active primary forms, 42.8% in patent active primary forms, and 82.8% in active postprimary forms. Tuberculous infections had a positively rate of 14.7%, while inactive postprimary tuberculosis had a positivity rate of 50%. The results obtained with A60 can favourably be compared with other serum ELISA tests for tuberculous antibodies against purified or semipurified mycobacterial antigens. Anti-A60 ELISA IgG antibody test can be useful to monitor the kinetics of humoral immunological response during tuberculous infection, disease and chemotherapy. A positive IgG ELISA test may support the diagnosis of active tuberculous disease.