Identification of antigens of Mycobacterium tuberculosis using human monoclonal antibodies

MDR-TB Antibody Response (Western Blot) to Fractions of Isoniazid and Rifampicin Resistant Antigens of Mycobacterium tuberculosis

Drug-resistant TB poses a major threat to control of TB worldwide. Despite progress in the detection of Multidrug-resistant TB (MDR-TB) cases, a major diagnostic gap remains: 55% of reported TB patients estimated to have MDR-TB were not detected in 2013. MDR-TB antigens were conjugated to CNBr-activated Sepharose 4B. Specific polyclonal antibodies against MDR-TB Ags were prepared in rabbits using two boosted injections of the MDR-TB antigen. The antibodies were purified and treated with susceptible TB to remove any non-specific and cross-reactive antibodies. In the present study, comparative analysis of electrophoretic pattern of different antigens of INH/RIF-resistant TB were studied for identifying protein profiles. A RIF-resistant TB antigen was shown here to have different protein profiles from INH-resistant TB isolate. The results of Western blotting analysis showed that in the RIF- and INH-resistant antigenic fractions some bands of 14.4 and 45 kDa as immunogenic were common. Moreover, four bands of RIF-resistant TB antigen fractions (16, 19, 21, and 45 KDa) and one band of INH-resistant TB (about 26 KDa) were detected as diagnostic antigens. This study suggests that the Western blot is an accurate test to survey INH- and RIF-resistant TB antigens of M. tuberculosis infection. These findings indicate that MDR-TB diagnosis (based on Ag detection) could be useful in the identification of disease stages that precede symptomatic and microbiologically positive TB, such as subclinical and incipient TB.

Diagnostic significance of humoral immune responses to recombinant antigens of Mycobacterium tuberculosis in patients with pleural tuberculosis

Mycobacterium tuberculosis bacilli are seldom demonstrated in tuberculous pleural effusion (TPE) by conventional bacteriological methods. In this study, an indirect enzyme-linked immunosorbent assay (ELISA) was developed to detect IgG against four mycobacterial recombinant antigens (ESAT-6, PlcA, HspX and Tb8.4) in 69 pleural fluids of patients with TPE and 71 patients with malignant pleural effusion. To increase the sensitivity of the assay, a multi-antigen cocktail containing all the above antigens were also used. IgG positivity in ELISA for PlcA, HspX, Tb8.4, ESAT-6 antigens and multi-antigen complex were 49.3, 60.8, 49.3, 53.6 and 75.4% respectively. Each one of the above four antigens and their multi-antigen cocktail were highly specific in distinguishing tuberculous and malignant pleural effusion. This new generation immunoassay will serve as a useful marker for the diagnosis of pleural tuberculosis patients in whom M. tuberculosis bacilli were not demonstrated by bacteriological methods.

Isolation of a 32 kDa Mycobacterium tuberculosis protein by lectin affinity chromatography

A 32 kDa antigen from delipidated M. tuberculosis H37Rv culture filtrate protein extract (CFPE) was purified by affinity chromatography on immobilized Lens culinaris lectin and electroelution. This antigen represents 0.4% of the total CFPE carbohydrate content and possesses galactose, xylose, mannose and GlcNAc (5:2:3:1 mol. ratio). A monoclonal antibody against the purified antigen reacted with the 32 kDa as well as a 30 kDa antigen in H37Rv CFPE, thus suggesting that both antigens represent closely related allelomorphic forms of the same antigen.

Identification of a novel antigen from Corynebacterium pseudotuberculosis that protects sheep against caseous lymphadenitis

A 40-kDa protein antigen from Corynebacterium pseudotuberculosis has been identified by application of a strategy that employs locally derived antibody-secreting cells (ASC). ASC probes generated by culture of ASC obtained from the lymph node draining the site of infection showed a specificity restricted to a 40-kDa antigen. Analysis of immunoblots with sequential serum samples taken from sheep during the course of experimental primary infection with C. pseudotuberculosis also revealed the 40-kDa antigen as an early immunodominant antigen. Sheep vaccinated with two 100-micrograms doses of a 40-kDa antigen preparation in aluminium hydroxide adjuvant were protected against infection with C. pseudotuberculosis, with an 82% reduction in the proportion of infected sheep and a 98% reduction in lung lesions. Sera from vaccinated sheep exhibited a strong response only to the 40-kDa antigen on immunoblots. These results strongly suggest that the 40-kDa antigen plays a major role in immunity to caseous lymphadenitis.

Identification of a Mycobacterium bovis BCG 45/47-kilodalton antigen complex, an immunodominant target for antibody response after immunization with living bacteria

Increased protection against a virulent challenge with Mycobacterium tuberculosis is induced mainly by a previous immunization with living avirulent mycobacteria, usually Mycobacterium bovis BCG. Only a transient and marginal protection is obtained after immunization with bacterial extracts or dead bacteria. Both living and heat-killed bacteria share a number of common antigens. In order to identify mycobacterial molecules which are dominant antigens during immunization with living bacteria, a two-step selection method was used. Two groups of guinea pigs were immunized either with living or with heat-killed BCG. Sera were then collected and used to select and counterselect antigens present in BCG culture filtrates. Each major fraction eluted from a series of high-pressure liquid chromatography columns (gel filtration, DEAE, and reverse-phase chromatography) was run on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transferred on polyvinylidene difluoride sheets. The molecules present on twin immunoblots were stained with antibodies raised in guinea pigs immunized either with living or with heat-killed BCG. Cross-reactive antigens stained in twin immunoblots were eliminated. Major antigens interacting with antibodies raised after immunization only with living bacteria were further purified. A complex of 45- and 47-kDa major molecules (45/47-kDa complex) was thus identified and further purified. The complex was found to interact only with antibodies present in sera of guinea pigs immunized with living bacteria and not at all with antibodies raised after immunization with dead bacteria. The 45/47-kDa antigen complex molecules were resolved on two-dimensional electrophoresis in three major and seven minor proteins detected with silver staining. All the molecules interacted with the antibodies present in sera of guinea pigs immunized with living BCG. The three major proteins (two at 47 kDa and one at 45 kDa) were amino-terminal sequenced. The sequence A-P-E-P-A-P-P-V-P-P-A-A-A-A-P-P-A, which was not previously reported, was the same for these three molecules. By using a competitive enzyme-linked immunosorbent assay, the concentrations of the 45/47-kDa antigen complex were measured in BCG culture filtrates, freeze-dried BCG, and dried heat-killed BCG; they were, respectively, 2, 0.01, and 0.001% of the total mass. The low or very low values compared with the high antibody concentration emphasized the ability of the 45/47-kDa complex delivered through live BCG to trigger an antibody response.

Identification by two-dimensional gel electrophoresis of a 58-kilodalton tumor necrosis factor-inducing protein of Mycobacterium tuberculosis

We have previously identified proteins in fractions of culture filtrate of Mycobacterium tuberculosis with the capacity to induce cytokine production in monocytes, by using a technique we defined as "monocyte Western blotting" (immunoblotting). In this series of experiments, we have extended this technique to two-dimensional gel electrophoresis and have identified a novel 58-kDa protein of M. tuberculosis which induces production of tumor necrosis factor by human monocytes. Nitrocellulose particles bearing this protein were used to develop murine monoclonal antibodies by the technique of intrasplenic immunization. The protein was purified by preparative isoelectric focusing and gel electrophoresis and subjected to N-terminal amino acid sequence analysis. As tumor necrosis factor is a mediator of both pulmonary necrosis and macrophage activation for intracellular killing, this 58-kDa protein may play an important role both in the immunopathogenesis of tuberculosis and in mycobacterial immunity.

T cell activation by mycobacterial antigens in inflammatory synovitis

To define which mycobacterial antigens were responsible for the activation of synovial fluid T lymphocytes, acetone-precipitated Mycobacterium tuberculosis (AP-MT) antigens were separated into five fractions following polyacrylamide gel electrophoresis and added to the mononuclear cell cultures of patients with inflammatory synovitis. Fractions 2 (50 to 70 kDa) and 5 (less than 28 kDa) resulted in significantly more proliferation than that of fractions 1, 3, and 4. The response to a purified mycobacterial 65-kDa heat shock protein (hsp), which migrated in fraction 2, was highly correlated (r = 0.89, P less than 0.001) with the response to the crude AP-MT. The proliferative response to a different hsp. the Escherichia coli DnaK, by synovial fluid lymphocytes was marginal. Analysis of the synovial fluid T cell response to mycobacterial culture filtrates by T cell Western blotting revealed dominant responses to antigen(s) in the range of 31 to 21 kDa in each responding patient, although no other consistent pattern of T cell activation was noted. Three lines of evidence suggested that the response to the low molecular weight fractions was directed against degradation fragments of the 65-kDa protein. These observations suggest that the activation of T lymphocytes obtained from inflammatory synovial fluids by crude mycobacterial antigens was due in large part to recognition of the 65-kDa mycobacterial hsp.

Human immune response to Mycobacterium tuberculosis antigens

Little is known about the immunodominant or protective antigens of Mycobacterium tuberculosis in humans. Cell-mediated immunity is necessary for protection, and healthy tuberculin-positive individuals are relatively resistant to exogenous reinfection. We compared the targets of the cell-mediated immune response in healthy tuberculin-positive individuals to those of tuberculosis patients and tuberculin-negative persons. By using T-cell Western blotting (immunoblotting) of nitrocellulose-bound M. tuberculosis culture filtrate, peaks of T-cell blastogenic activity were identified in the healthy tuberculin reactors at 30, 37, 44, 57, 64, 71 and 88 kDa. Three of these fractions (30, 64, and 71 kDa) coincided with previously characterized proteins: antigen 6/alpha antigen, HSP60, and HSP70, respectively. The blastogenic responses to purified M. tuberculosis antigen 6/alpha antigen and BCG HSP60 were assessed. When cultured with purified antigen 6/alpha antigen, lymphocytes of healthy tuberculin reactors demonstrated greater [3H]thymidine incorporation than either healthy tuberculin-negative controls or tuberculous patients (8,113 +/- 1,939 delta cpm versus 645 +/- 425 delta cpm and 1,019 +/- 710 delta cpm, respectively; P less than 0.01). Healthy reactors also responded to HSP60, although to a lesser degree than antigen 6/alpha antigen (4,276 +/- 1,095 delta cpm; P less than 0.05). Partially purified HSP70 bound to nitrocellulose paper elicited a significant lymphocyte blastogenic response in two of six of the tuberculous patients but in none of the eight healthy tuberculin reactors. Lymphocytes of none of five tuberculin-negative controls responded to recombinant antigens at 14 or 19 kDa or to HSP70. Antibody reactivity generally was inversely correlated with blastogenic response: tuberculous sera had high titer antibody to M. tuberculosis culture filtrate in a range from 35 to 180 kDa. This is the first systematic evaluation of the human response to a panel of native and recombinant antigens in healthy tuberculin reactors and tuberculous patients. Antigens which stimulated prominent lymphocyte blastogenic responses were identified in seven fractions on T-cell Western blot analysis. Two of these may represent previously characterized proteins; the others may contain immunodominant proteins that will require further characterization.

Pleuritis as a manifestation of reactivation tuberculosis

PURPOSE

The purpose of this study was to determine the frequency with which tuberculous pleuritis is a manifestation of reactivation tuberculosis and to compare the clinical manifestations of reactivation tuberculous pleuritis with "classic" tuberculous pleuritis, in which chest roentgenograms reveal no parenchymal infiltrates.

PATIENTS AND METHODS

We evaluated the medical records of 59 patients in whom tuberculous pleuritis was confirmed by histologic findings or mycobacterial culture. Twenty-seven patients (46%) had typical chest roentgenographic findings of reactivation tuberculosis, whereas 32 (54%) had classic tuberculous pleuritis. The clinical and laboratory features of these two groups were compared.

RESULTS

Symptoms were more prolonged and pleural fluid glucose and lactate dehydrogenase concentrations were more markedly abnormal in patients with reactivation pleuritis than in those with classic pleuritis, suggesting a more chronic inflammatory process in the former group. Compared with patients with classic tuberculous pleuritis, those with reactivation pleuritis had a lower frequency of reactive tuberculin skin tests (61% versus 88%) and granulomatous pleural inflammation (25% versus 72%), but a higher bacillary burden, manifest by a higher frequency of positive sputum smears for acid-fast bacilli (50% versus 0%) and positive mycobacterial cultures from sputum (60% versus 23%) and pleural fluid (91% versus 66%).

CONCLUSIONS

In contrast to previous reports, tuberculous pleuritis was a manifestation of reactivation tuberculosis in 46% (27 of 59) of patients. Tuberculous pleuritis is a more chronic process in patients with reactivation disease than in those with classic pleuritis. The lower frequency of reactive tuberculin skin tests and granuloma formation, combined with the higher bacillary burden in patients with reactivation pleuritis, suggest that these patients mount a less effective immune response to Mycobacterium tuberculosis infection than do patients with the classic form of tuberculous pleuritis.

Induction of interleukin 1 and tumor necrosis factor by mycobacterial proteins: the monocyte western blot

Infection with Mycobacterium tuberculosis involves mononuclear phagocytic cells as hosts to intracellular parasites, accessory cells in the induction of the immune response, effector cells for mycobacterial killing, and targets of cytotoxic lymphocytes. When stimulated by whole mycobacteria or various mycobacterial preparations, monocytes and macrophages produce the cytokines interleukin 1 and tumor necrosis factor, which possess multiple functions, including immune induction, and may be responsible for the fever and cachexia prominent in tuberculosis. To identify mycobacterial proteins that may directly activate production of these cytokines, culture filtrate of M. tuberculosis that had been subjected to gel electrophoresis and transferred to nitrocellulose paper was used to stimulate monocyte production of cytokines. Fractions representing molecular weights of 46,000 and 20,000 consistently induced both interleukin 1 and tumor necrosis factor. The magnitude of the monocyte responses to these fractions was similar to that to intact mycobacteria or optimal concentrations of lipopolysaccharide. This stimulatory effect was not due to contamination with either bacterial lipopolysaccharide or mycobacterial lipoarabinomannan, as it was abolished by digestion with Streptomyces griseus protease but was unaffected by ammonium sulfate precipitation, preincubation with polymyxin B, or depletion of lipoarabinomannan by immunoaffinity chromatography. Proteins identified by this system may have considerable potential as immunogens, as the capacity to directly stimulate mononuclear phagocyte production of cytokines is an essential property of adjuvants.