Identification and characterization of antigenic determinants of Mycobacterium leprae that react with antibodies in sera of leprosy patients

The continuing challenges of leprosy

Leprosy is best understood as two conjoined diseases. The first is a chronic mycobacterial infection that elicits an extraordinary range of cellular immune responses in humans. The second is a peripheral neuropathy that is initiated by the infection and the accompanying immunological events. The infection is curable but not preventable, and leprosy remains a major global health problem, especially in the developing world, publicity to the contrary notwithstanding. Mycobacterium leprae remains noncultivable, and for over a century leprosy has presented major challenges in the fields of microbiology, pathology, immunology, and genetics; it continues to do so today. This review focuses on recent advances in our understanding of M. leprae and the host response to it, especially concerning molecular identification of M. leprae, knowledge of its genome, transcriptome, and proteome, its mechanisms of microbial resistance, and recognition of strains by variable-number tandem repeat analysis. Advances in experimental models include studies in gene knockout mice and the development of molecular techniques to explore the armadillo model. In clinical studies, notable progress has been made concerning the immunology and immunopathology of leprosy, the genetics of human resistance, mechanisms of nerve injury, and chemotherapy. In nearly all of these areas, however, leprosy remains poorly understood compared to other major bacterial diseases.

Analysis of the shotgun expression library of the Mycobacterium tuberculosis genome for immunodominant polypeptides: potential use in serodiagnosis

A recombinant DNA strategy was applied to analyze and screen the shotgun expression library from a clinically confirmed local virulent isolate of Mycobacterium tuberculosis with sera from tuberculosis patients, which led to expression and purification of highly immunoreactive and specific mycobacterial antigens expressed during the course of active disease which could be of diagnostic significance. An enzyme-linked immunoassay for diagnosis of tuberculosis was devised by using a shotgun immunoexpression library in the lambdagt11 vector. DNA from a virulent M. tuberculosis patient isolate (TBW-33) confirmed with the BACTEC 460 system was sheared and expressed to generate shotgun polypeptides. beta-Galactosidase fusion proteins capable of demarcating active tuberculosis infections from Mycobacterium bovis BCG-vaccinated healthy subjects or people harboring environmental mycobacteria were selected by comparative immunoreactivity studies. Promising mycobacterial DNA cassettes were subcloned and expressed into the glutathione S-transferase (GST) fusion vector pGEX-5X-1 with a strong tac promoter and were expressed in Escherichia coli BL21. These fusion proteins were severed at a built-in factor Xa recognition site to separate the GST tags and were utilized in an indirect enzyme-linked immunoassay for serodiagnosis of patients with active tuberculosis. The system offered a clear demarcation between BCG-vaccinated healthy subjects and patients with active tuberculosis and proved to be effective in detecting pulmonary as well as extrapulmonary tuberculosis, with an overall sensitivity of 84.33% and an overall specificity of 93.62%.

Selective identification of new therapeutic targets of Mycobacterium tuberculosis by IVIAT approach

The in vivo induced antigen technology (IVIAT)(1) has been used for the identification of open reading frames (ORFs) which could be possible therapeutic targets. A recombinant lambdagt11:: Mycobacterium tuberculosis H37Rv expression library was screened with pooled TB patient sera preabsorbed with in vitro grown M. tuberculosis H37Rv. Preabsorption of pooled TB patient sera allowed identification of antigens specifically expressed or upregulated during infection and growth in vivo. Six ORFs were identified, of which four (rv0287, rv2402, rv3878 and rv1045) were of hypothetical functions. Rv0287 is a probable regulatory protein. Rv3878 is present uniquely in M. tuberculosis H37Rv and is a part of RDI deletion region of M. bovis BCG, which includes esat 6 region. This could be exploited as a tool for diagnosis. Two ORFs were assigned function solely on the basis of homology, dnaQ (rv3711c) and lpdA (rv3303c). dnaQ codes for the epsilon subunit of DNA polymerase III, which is responsible for the proofreading activity of the complex. lpdA codes for dihydrolipoamide dehydrogenase, which is a part of many multienzyme complexes such as pyruvate dehydrogenase, keto-acid dehydrogenase and alpha-ketoglutarate dehydrogenase. These two enzymes appear to be potential targets for drug development.

Identification and characterization of the ESAT-6 homologue of Mycobacterium leprae and T-cell cross-reactivity with Mycobacterium tuberculosis

In this paper we describe identification and characterization of Mycobacterium leprae ESAT-6 (L-ESAT-6), the homologue of M. tuberculosis ESAT-6 (T-ESAT-6). T-ESAT-6 is expressed by all pathogenic strains belonging to the M. tuberculosis complex but is absent from virtually all other mycobacterial species, and it is a promising antigen for immunodiagnosis of tuberculosis (TB). Therefore, we analyzed whether L-ESAT-6 is a similarly powerful tool for the study of leprosy by examining T-cell responses against L-ESAT-6 in leprosy patients, TB patients, and exposed or nonexposed healthy controls from areas where leprosy and TB are endemic and areas where they are not endemic. L-ESAT-6 was recognized by T cells from leprosy patients, TB patients, individuals who had contact with TB patients, and healthy individuals from an area where TB and leprosy are endemic but not by T cells from individuals who were not exposed to M. tuberculosis and M. leprae. Moreover, leprosy patients who were not responsive to M. leprae failed to respond to L-ESAT-6. A very similar pattern was obtained with T-ESAT-6. These results show that L-ESAT-6 is a potent M. leprae antigen that stimulates T-cell-dependent gamma interferon production in a large proportion of individuals exposed to M. leprae. Moreover, our results suggest that there is significant cross-reactivity between T-ESAT-6 and L-ESAT-6, which has implications for the use of ESAT-6 as tool for diagnosis of leprosy and TB in areas where both diseases are endemic.

The ESAT-6 gene cluster of Mycobacterium tuberculosis and other high G+C Gram-positive bacteria

BACKGROUND

The genome of Mycobacterium tuberculosis H37Rv has five copies of a cluster of genes known as the ESAT-6 loci. These clusters contain members of the CFP-10 (lhp) and ESAT-6 (esat-6) gene families (encoding secreted T-cell antigens that lack detectable secretion signals) as well as genes encoding secreted, cell-wall-associated subtilisin-like serine proteases, putative ABC transporters, ATP-binding proteins and other membrane-associated proteins. These membrane-associated and energy-providing proteins may function to secrete members of the ESAT-6 and CFP-10 protein families, and the proteases may be involved in processing the secreted peptide.

RESULTS

Finished and unfinished genome sequencing data of 98 publicly available microbial genomes has been analyzed for the presence of orthologs of the ESAT-6 loci. The multiple duplicates of the ESAT-6 gene cluster found in the genome of M. tuberculosis H37Rv are also conserved in the genomes of other mycobacteria, for example M. tuberculosis CDC1551, M. tuberculosis 210, M. bovis, M. leprae, M. avium, and the avirulent strain M. smegmatis. Phylogenetic analyses of the resulting sequences have established the duplication order of the gene clusters and demonstrated that the gene cluster known as region 4 (Rv3444c-3450c) is ancestral. Region 4 is also the only region for which an ortholog could be found in the genomes of Corynebacterium diphtheriae and Streptomyces coelicolor.

CONCLUSIONS

Comparative genomic analysis revealed that the presence of the ESAT-6 gene cluster is a feature of some high-G+C Gram-positive bacteria. Multiple duplications of this cluster have occurred and are maintained only within the genomes of members of the genus Mycobacterium.

HLA-Class II-Associated Control of Antigen Recognition by T Cells in Leprosy: A Prominent Role for the 30/31-kDa Antigens

The recognition of 16 mycobacterial Ags by a panel of T cell lines from leprosy patients and healthy exposed individuals from an endemic population was examined within the context of expressed HLA-DR molecules. Although overall no significant differences were found between the frequencies of Ag recognition in the different subject groups, when Ag-specific T cell responses were examined within the context of HLA-DR, a highly significant difference was found in the recognition of the 30/31-kDa Ag. HLA-DR3 appeared to be associated with high T cell responsiveness to the 30/31-kDa Ag in healthy contacts (p = 0.01), but, conversely, with low T cell responsiveness to this Ag in tuberculoid patients (p = 0.005). Within the group of HLA-DR3-positive individuals, differences in 30/31-kDa directed T cell responsiveness were highly significant not only between healthy individuals and tuberculoid patients (p < 0.0001), but also between healthy individuals and lepromatous patients (p = 0.009), and consequently between healthy individuals compared with leprosy patients as a group (p < 0.0001). A dominant HLA-DR3-restricted epitope was recognized by healthy contacts in this population. It has been proposed that secreted Ags may dominate acquired immunity early in infection. The low T cell response to the secreted, immunodominant 30/31-kDa Ag in HLA-DR3-positive leprosy patients in this population may result in retarded macrophage activation and delayed bacillary clearance, which in turn may lead to enhanced Ag load followed by T cell-mediated immunopathology.

A Mycobacterium tuberculosis operon encoding ESAT-6 and a novel low-molecular-mass culture filtrate protein (CFP-10)

The early secreted antigenic target 6 kDa protein (ESAT-6) is a potent T-cell protein antigen synthesized by Mycobacterium tuberculosis. Its corresponding gene (esat-6) is located in RD1, a 10 kb DNA region deleted in the attenuated tuberculosis vaccine strain Mycobacterium bovis BCG. The promoter region of M. tuberculosis esat-6 was cloned and characterized. A new gene, designated lhp and cotranscribed with esat-6, was identified. Moreover, computer searches in the M. tuberculosis genome identified 13 genes related to the lhp/esat-6 operon, defining a novel gene family. The transcription initiation sites of the lhp/esat-6 operon were mapped using M. tuberculosis RNA. The corresponding promoter signals were not recognized in Mycobacterium smegmatis, in which transcription of lhp/esat-6 is initiated at different locations. The M. tuberculosis lhp gene product was identified as CFP-10, a low-molecular-mass protein found in the short-term culture filtrate. These results show that the genes encoding CFP-10 and ESAT-6 are transcribed together in M. tuberculosis and that both code for small exported proteins.

Isolation of recombinant phage clones expressing mycobacterial T cell antigens by screening a recombinant DNA library with human CD4+ Th1 clones

A lambda gt11 recombinant DNA library of Mycobacterium leprae was screened to isolate recombinant phage clones expressing mycobacterial antigens important for T cell reactivity. The library was plated on a lawn of Escherichia coli Y1090 and recombinant antigens were expressed from isolated phage clones in 96-well plates. Pools of recombinant antigens from 12 wells were tested in T cell proliferation assays with MHC class II restricted human CD4+ Th1 clones secreting interferon-gamma and cytotoxic for antigen pulsed antigen presenting cells. By screening 1750 pools of recombinant antigens with a mixture of eight Th1 clones, we identified two recombinant phage clones that expressed recombinant mycobacterial antigens stimulatory for T cells. MHC restriction analysis and reactivity to a battery of mycobacterial antigens suggested that the two responding Th1 clones recognized mycobacterial antigens/epitopes with different MHC class II (HLA-DR) restriction requirements. Our results suggest that the methodology described in this paper is suited to isolate recombinant phage clones expressing mycobacterial recombinant antigens stimulatory for T cells of protective phenotype. Such antigens may be useful in designing new vaccines and diagnostic reagents against mycobacterial diseases.

Identification of epitopes of fibronectin attachment protein (FAP-A) of Mycobacterium avium which stimulate strong T-cell responses in mice

The T-cell response to fibronectin attachment protein (FAP-A) in BALB/c and B10.BR mice was examined. Both strains developed strong T-cell responses to FAP-A, directed to single, unique epitopes. T cells from mice infected with Mycobacterium avium responded to FAP-A, suggesting a possible role in a protective immune response.

Analysis of a genomic DNA expression library of Mycobacterium tuberculosis using tuberculosis patient sera: evidence for modulation of host immune response

DNA obtained from a human sputum isolate of Mycobacterium tuberculosis, NTI-64719, which showed extensive dissemination in the guinea pig model resulting in a high score for virulence was used to construct an expression library in the lambda ZAP vector. The size of DNA inserts in the library ranged from 1 to 3 kb, and recombinants represented 60% of the total plaques obtained. When probed with pooled serum from chronically infected tuberculosis patients, the library yielded 176 recombinants with a range of signal intensities. Among these, 93 recombinants were classified into 12 groups on the basis of DNA hybridization experiments. The polypeptides synthesized by the recombinants were predominantly LacZ fusion proteins. Serum obtained from patients who were clinically diagnosed to be in the early phase of M. tuberculosis infection was used to probe the 176 recombinants obtained. Interestingly, some recombinants that gave very strong signals in the original screen did not react with early-phase serum; conversely, other whose signals were extremely weak in the original screen gave very intense signals with serum from recently infected patients. This indicates the differential nature of either the expression of these antigens or the immune response elicited by them as a function of disease progression.

Molecular characterization and T-cell-stimulatory capacity of Mycobacterium leprae antigen T5

A Mycobacterium leprae lambda gt11 clone designated T5 has previously been selected with sera from tuberculoid leprosy patients. Sequence analysis of this clone revealed the presence of two overlapping open reading frames (ORFs) present on the two cDNA strands. The first ORF codes for the serologically recognized antigen, which was fused with the lacZ gene in the lambda gt11 clone. The second ORF, present on the complementary strand, displays strong sequence homology with the aspartyl-tRNA synthetase genes of Escherichia coli and Thermus thermophilus. Here we show that the purified T5-derived product, overexpressed in E. coli, is recognized by T cells of the majority of the leprosy patients tested, including lepromatous leprosy patients who do not respond to whole M. leprae bacilli.

The 65 kDa protein of Mycobacterium habana and its putative role in immunity against experimental tuberculosis

Mycobacteria including Mycobacterium tuberculosis and Mycobacterium leprae possess multiple antigens some of which inhibit other anti-mycobacterial immune responses. Whole cell vaccines are not free from these suppressive molecules and may adversely affect the immunogenic response(s). Purified protein components having only immunogenic properties should prove to be superior vaccine(s). Mycobacterium habana, a candidate vaccine for mycobacterial infections has been dissected for analysing its antigenic myriad. A 65 kDa protein of this mycobacterium has been isolated and characterized for its protective and cell mediated immune responses. The protein was isolated in pure form using an isotachophoresis (SDS-PAGE filtration) technique and identified with low molecular weight markers along with mAb using the immunoblot technique. Mab IIH9 has identified a 65 kDa protein in M. habana. This protein has been found to be immunoprotective in mice against M. tuberculosis H37Rv infection. It generates high levels of DTH responses in mice against M. tuberculosis and M. leprae antigens and inhibits migration of sensitized cells under the antigenic influence of homologous and heterologous origin. Possibilities of developing this protein as a subunit vaccine are discussed in this report.

A Mycobacterium leprae gene encoding a fibronectin binding protein is used for efficient invasion of epithelial cells and Schwann cells

Mycobacterium leprae, the causative agent of leprosy, is an obligate intracellular pathogen. M. leprae can infect a variety of cells in vivo, including epithelial cells, muscle cells, and Schwann cells, in addition to macrophages. The ligand-receptor interactions important in the attachment and ingestion of M. leprae by these nonmacrophage cells remains unknown. Fibronectin (FN) significantly enhances both attachment and ingestion of M. leprae by epithelial and Schwann cell lines. We cloned an M. leprae FN binding protein (FN attachment protein [FAP]) distinct from the 85ABC complex which has been shown previously to bind FN. The FAP open reading frame predicts a protein of 29.5 kDa with a 39-amino-acid signal peptide and was previously described as an antigen in leprosy patients. M. leprae FAP has homologies in M. vaccae, M. avium, and M. tuberculosis, as determined by Southern blotting and direct peptide analysis. Both anti-FAP antibodies and an Escherichia coli-expressed recombinant protein significantly blocked M. leprae attachment and internalization by T-24, an epithelial cell line, and JS1, a Schwann cell line. These data suggest that FN can be a bridging opsonic ligand for attachment of mycobacteria to nonphagocytes and that FAP plays an important role in this process. This may be an important step in the initiation of M. leprae infection in vivo.

Unique gene organization of thioredoxin and thioredoxin reductase in Mycobacterium leprae

The thioredoxin system comprising thioredoxin (Trx), thioredoxin reductase (TR) and NADPH operates via redox-active disulphides and provides electrons for a wide variety of different metabolic processes in prokaryotic and eukaryotic cells. Thioredoxin is also a general protein disulphide reductase involved in redox regulation. In bacteria, the Trx and TR proteins previously identified were encoded by separate genes (trxA and trxB). In this study, we report a novel genomic organization of TR and Trx in mycobacteria and show that at least three modes of organization of TR and Trx genes can exist within a single bacterial genus: (i) in the majority of mycobacterial strains the genes coding for TR and Trx are located on separate sites of the genome; (ii) interestingly, in all pathogenic Mycobacterium tuberculosis complex mycobacteria both genes are found on the same locus, overlapping in one nucleotide; (iii) in the pathogen Mycobacterium leprae, TR and Trx are encoded by a single gene. Sequence analysis of the M. leprae gene demonstrated that the N-terminal part of the protein corresponds to TR and the C-terminal part to Trx. A corresponding single protein product of approximately 49 kDa was detected in cell extracts of M. leprae. These findings demonstrate the very unusual phenomenon of a single gene coding for both the substrate (thioredoxin) and the enzyme (thioredoxin reductase), which seems to be unique to M. leprae.

Molecular and immunological characterization of the highly conserved antigen 84 from Mycobacterium tuberculosis and Mycobacterium leprae

Crossed immunoelectrophoresis (CIE) has been used to develop a reference system for classifying mycobacterial antigens. The subsequent use of specific antibodies allowed further determination of antigens by molecular weight. The monoclonal antibody F126-2, originally raised against a 34-kDa antigen of Mycobacterium kansasii, reacted with antigen 84 (Ag84) in the CIE reference system for Mycobacterium bovis BCG and Mycobacterium tuberculosis. To characterize Ag84, we screened a lambda gt11 gene library from M. tuberculosis with antibody F126-2 and identified the encoding gene. The corresponding Mycobacterium leprae Ag84 gene was subsequently selected from a cosmid library, using the M. tuberculosis gene as a probe. Both genes were expressed as 34-kDa proteins in Escherichia coli, and the recombinant proteins indeed corresponded to Ag84 in the CIE reference system. The derived amino acid sequences of the M. tuberculosis and M. leprae proteins showed 85% identity, which indicates that Ag84 constitutes a group of highly conserved mycobacterial antigens. Antibodies of almost 60% of lepromatous leprosy patients responded to Ag84, indicating that the protein is highly immunogenic following infection in multibacillary leprosy.

Characterization of a Mycobacterium leprae antigen related to the secreted Mycobacterium tuberculosis protein MPT32

Secreted proteins may serve as major targets in the immune response to mycobacteria. To identify potentially secreted Mycobacterium leprae antigens, antisera specific for culture filtrate proteins of Mycobacterium tuberculosis were used to screen a panel of recombinant antigens selected previously by leprosy patient sera. Four potentially secreted antigens were identified by this approach, and one was recognized by antibodies specific for MPT32, a secreted M. tuberculosis protein. The DNA coding for the M. leprae antigen, which we have designated 43L, was isolated and characterized and found to encode a 25.5-kDa protein that is preceded by a consensus signal peptide of 39 amino acids. The N-terminal amino acid sequence of 43L shows 50% homology with the 20 known N-terminal amino acids of MPT32, and 47% homology was found with the N terminus of a 45/47-kDa antigen complex identified in Mycobacterium bovis BCG. These findings indicate that 43L represents an antigen related to MPT32 and the M. bovis BCG 45/47-kDa complex and that 43L is likely to be a protein secreted by M. leprae. Purified recombinant 43L protein is recognized by antibodies and T cells from healthy contacts and leprosy patients, illustrating that secreted proteins are of importance in the immune response to M. leprae.

A Mycobacterium leprae-specific gene encoding an immunologically recognized 45 kDa protein

By screening a Mycobacterium leprae lambda gt11 expression library with a serum from an Ethiopian lepromatous leprosy (LL) patient a clone was isolated (LL4) belonging to hybridization group III of a panel of previously isolated M. leprae clones. Members of this hybridization group encode a serologically recognized 45 kDa protein. The complete DNA sequences of the partially overlapping clones LL4 and L1 (hybridization group III) are presented and these revealed the presence of an open reading frame (ORF) predicting a protein with a molecular size of 42,448 Da. Southern hybridizations on total genomic DNA of M. leprae, Mycobacterium tuberculosis and eight atypical mycobacteria showed that the LL4 DNA fragment is specific for M. leprae DNA even under low-stringency conditions. The M. leprae specificity of LL4 DNA was further confirmed by the polymerase chain reaction using four different sets of primers. Western blotting analyses showed that the M. leprae 45 kDa protein is frequently recognized by antibodies from leprosy patients and that this recognition is specific since no antibodies could be detected in sera of tuberculosis patients. T-cell proliferation assays also demonstrated T-cell recognition by leprosy patients and healthy contacts of the M. leprae 45 kDa protein. The specificity of the LL4 DNA region and the 45 kDa antigen that is encoded by hybridization group III could provide unique tools for the development of M. leprae-specific immunological and DNA reagents.

Sequence and immunological characterization of a serine-rich antigen from Mycobacterium leprae

Sera from lepromatous leprosy patients were used to screen a Mycobacterium leprae lambda gt11 library. Three positive plaques were picked, and lysogens were constructed. Immunoblot analysis showed that all of the lysogens expressed an apparently identical beta-galactosidase fusion protein which reacted strongly with the sera. The 1.7-kbp insert from one clone was subcloned into the lacZ gene in pUR290; sequence analysis of the end fused to lacZ revealed an open reading frame with no significant homology to previously published sequences. The insert was used to screen an M. leprae cosmid library, and five clones were isolated. The insert was also found to hybridize to clones expressing the M. leprae antigen which had previously been designated class III and 25L. A 1.8-kbp HindIII fragment was subcloned from one of the cosmids and sequenced. The sequence revealed a 1,227-bp open reading frame, encoding a 408-amino-acid protein with a predicted molecular mass of 42,466 Da. The protein contains amino- and carboxy-terminal hydrophobic domains and a hydrophilic central domain; the amino-terminal domain shows some homology to a 51-kDa hypothetical antigen of Mycobacterium tuberculosis, while the hydrophilic region contains a high proportion of serine residues, and we have therefore designated the protein serine-rich antigen (Sra). Some repeated motifs are present in the protein, but their significance is unknown. Seventy-eight percent of serum samples from multibacillary leprosy patients and 68% of serum samples from paucibacillary leprosy patients recognized the fusion protein, showing that this is a major M. leprae antigen. In contrast, all serum samples from endemic controls were negative, while 26% of serum samples from tuberculosis patients were weakly positive.

Use of an ordered cosmid library to deduce the genomic organization of Mycobacterium leprae

In an attempt to unify the genetic and biological research on Mycobacterium leprae, the aetiological agent of leprosy, a cosmid library was constructed and then ordered by a combination of fingerprinting and hybridization techniques. The genome of M. leprae is represented by four contigs of overlapping clones which, together, account for nearly 2.8Mb of DNA. Several arguments suggest that the gaps between the contigs are small in size and that virtually complete coverage of the chromosome has been obtained. All of the cloned M. leprae genes have been positioned on the contig maps together with the 29 copies of the dispersed repetitive element, RLEP. These have been classified into four groups on the basis of differences in their organization. Several key housekeeping genes were identified and mapped by hybridization with heterologous probes, and the current genome map of this uncultivable pathogen comprises 72 loci.

Cloning of mycobacterial histidine synthesis genes by complementation of a Mycobacterium smegmatis auxotroph

Histidine-requiring auxotrophs of Mycobacterium smegmatis were isolated following N-methyl-N'-nitro-N-nitrosoguanidine treatment. One of these mutants, his5, was transformed with an M. smegmatis shuttle cosmid library, and complementing clones were isolated at a frequency of approximately 1%. A 2.3 kb fragment was subcloned and sequenced, and found to contain the start of an operon including the hisD gene and part of the hisC gene. No hisG gene was detected upstream of hisD, suggesting that the regulation of histidine biosynthesis in mycobacteria may differ from that of Escherichia coli. The strategy used here will allow the molecular genetics of complex mycobacterial-specific biosynthetic pathways involved in the virulence of pathogenic species to be studied.

Cellular immune response to the cell walls of Mycobacterium leprae in leprosy patients and healthy subjects exposed to leprosy

Cell walls of M. leprae consist of complex arrangements of carbohydrate, lipid, peptidoglycan and protein molecules. Recently, extractable proteins of a wide range of molecular weights were identified as components of the cell wall. We have examined the cellular immune responses of Nepali leprosy patients to a cell wall preparation of M. leprae enriched for these proteins. Strong lymphocyte proliferative responses to the antigens were present in half of the paucibacillary leprosy patients and in the majority of healthy control subjects with occupational exposure to leprosy. Patients with multibacillary disease responded poorly and patients with tuberculosis had intermediate responses. Proliferative responses to the cell wall protein fraction were strongly correlated to the proliferative responses to sonicates of the whole leprosy bacillus. Immunization of mice with cell wall proteins resulted in inhibition of growth of M. leprae following foot-pad inoculation with viable organisms. Therefore cell-mediated immune responses to the extractable proteins of the cell wall may play a role in protective immunity against M. leprae infection.

Mycobacteria contain two groEL genes: the second Mycobacterium leprae groEL gene is arranged in an operon with groES

In contrast to other bacterial species, mycobacteria were thus far considered to contain groEL and groES genes that are present on separate loci on their chromosomes, Here, by screening a Mycobacterium leprae lambda gt11 expression library with serum from an Ethiopian lepromatous leprosy patient, two DNA clones were isolated that contain a groEL gene arranged in an operon with a groES gene. The complete DNA sequence of this groESL operon was determined. The predicted amino acid sequences of the GroES and GroEL proteins encoded by this operon are 85-90% and 59-61% homologous to the sequences from previously characterized mycobacterial GroES and GroEL proteins. Southern blotting analyses with M. leprae groES- and groEL-specific probes demonstrate that similar groESL homologous DNA is present in the genomes of other mycobacteria, including Mycobacterium tuberculosis. This strongly suggests that mycobacteria contain a groESL operon in addition to a separately arranged second groEL gene. Using five T-cell clones from two leprosy patients as probes, expression of the M. leprae GroES protein in Escherichia coli after heat shock was demonstrated. Four of these clones recognized the same M. leprae-specific GroES-derived peptide in a DR2-restricted fashion. No expression of the groEL gene from this operon was detected in E. coli after heat shock, as tested with a panel of T-cell clones and monoclonal antibodies reactive to previously described GroEL proteins of mycobacteria.

Molecular and immunological analysis of a fibronectin-binding protein antigen secreted by Mycobacterium leprae

By screening a Mycobacterium leprae lambda gt11 genomic DNA library with leprosy-patient sera we have previously identified 50 recombinant clones that expressed novel M. leprae antigens (Sathish et al., 1990). In this study, we show by DNA sequencing and immunoblot analysis that three of these clones express a M. leprae homologue of the fibronectin-binding antigen 85 complex of mycobacteria. The complete gene was characterized and it encodes a 327-amino-acid polypeptide, consisting of a consensus signal sequence of 38 amino acids followed by a mature protein of 289 amino acids. This is the first sequence of a member of the M. leprae antigen 85 complex, and Southern blotting analysis indicated the presence of multiple genes of the 85 complex in the genome of M. leprae. The amino acid sequence displays 75-85% sequence identity with components of the antigen 85 complex from M. tuberculosis, M. bovis BCG and M. kansasii. Furthermore, antibodies to the antigen 85 complex of M. tuberculosis and M. bovis BCG reacted with two fusion proteins containing the amino acid regions 55-266 and 266-327 of the M. leprae protein. The M. leprae 30/31 kDa protein induces strong humoral and cellular responses, as judged by Western blot analysis with patient sera and proliferation of T cells derived from healthy individuals and leprosy patients. Amino acid regions 55-266 and 265-327 both were shown to bind to fibronectin, indicating the presence of at least two fibronectin-binding sites on the M. leprae protein. These data indicate that this 30/31 kDa protein is not only important in the immune response against M. leprae, but may also have a biological role in the interaction of this bacillus with the human host.

Localization of the steroid 1-dehydrogenase in Rhodococcus erythropolis IMET 7030 by immunoelectron microscopy

The steroid 1-dehydrogenase of Rhodococcus erythropolis IMET 7030, an active steroid-transforming strain, was localized by immunogold labelling both in cells induced with 17-alpha-methyl-testosterone and in noninduced cells. The labelling intensity was much higher in induced cells than in noninduced cells, indicating increased enzyme production in the case of induction. Using the postembedding procedure, the main portion of the enzyme was found in the peripheral region of the cytoplasm. A considerable amount was bound in clusters to the inner side of the cytoplasmic membrane. The enzyme was also detected in channels connecting the cytoplasm with the cell surface. By means of the preembedding labelling, a few gold clusters could be detected on the cell surface. The significance of this observation was discussed.

Overexpression of a Rhodococcus erythropolis protein in Escherichia coli with immunological identity to the Rhodococcus steroid 1-dehydrogenase. Immunoelectron microscopic localization and electrophoretic studies

The recombinant Escherichia coli K-12 strain chi 6060 harbouring the plasmid pYA 1201 with a gene from Rhodococcus erythropolis IMET 7030 overexpressed a protein which reacts with a monospecific antiserum against the steroid 1-dehydrogenase (Sdh) from the same Rhodococcus strain. It was shown previously that this recombinant protein exhibits no enzymatic activity. By immunogold labelling the protein was localized on ultrathin sections of the recombinant E. coli strain. After cultivation at 37 degrees C it was found within large cytoplasmic compartments (inclusion bodies). The inclusion bodies occupied 40% to 75% of the sectioned cell area. The highest amount of protein was observed after induction of the culture with isopropyl-beta-D-thiogalactopyranoside. Approximately 20% of the induced cells became enlarged (up to 5-fold of the normal size) and deformed; multiplication of the Rhodococcus protein producing cells was inhibited. After ultrasonic cell disintegration the inclusion bodies were found only in the fraction of the sedimented cell debries and did still react with anti-Sdh. When recombinant E. coli cells were cultivated at 28 degrees C, inclusion bodies appeared very seldom and the immunoreactive protein was distributed throughout the whole cytoplasm.

Identification of Mycobacterium leprae antigens from a cosmid library: characterization of a 15-kilodalton antigen that is recognized by both the humoral and cellular immune systems in leprosy patients

Screening of the Mycobacterium leprae cosmid library with pooled sera from lepromatous leprosy (LL) patients by a colony immunoblot technique resulted in the identification of about 100 colonies that produced immunologically reactive proteins. Twenty-four of these clones were purified, analyzed, and found to comprise two groups according to the reactivity of the recombinant proteins with LL sera and to the DNA restriction patterns of the recombinant plasmids and cosmids. Proteins specified by clones from group I reacted strongly with LL patients' sera on a Western blot (immunoblot), demonstrating a 15-kDa protein band designated A15. The A15 antigen also reacted with pooled sera from patients with tuberculoid leprosy from the United States and Brazil. Clones from group II did not show any reactive protein band on a Western blot, when reacted with patients' sera. DNAs from cosmids of group II all contain a 10-kb PstI fragment that hybridized to the unique repetitive M. leprae DNA. Sequence analysis of a 1.2-kb fragment containing the entire coding sequence of A15 revealed three open reading frames (ORFs), only one of which (ORF II) contains sufficient genetic information to encode for A15. Part of the A15 gene was found to exist also in a group of lambda gt11:M. leprae clones previously isolated in our laboratory by immunological screening with LL patients' sera. One of the lambda gt11 clones (L8) expresses a beta-galactosidase fusion protein with 89 amino acids from the C terminus of A15. An important result was that the fusion protein was clearly recognized by T cells from leprosy patients. Interestingly, Mycobacterium tuberculosis-stimulated T cells from M. leprae nonresponder (LL as well as borderline tuberculoid) patients were able to respond to the isolated recombinant M. leprae antigen, indicating that nonresponsiveness to M. leprae antigens can be reversible. The sequence of the M. leprae DNA fused to the beta-galactosidase gene of lambda gt11 clone L8 was identical to that of a lambda gt11:M. leprae clone isolated recently that expresses an immunologically reactive fusion protein (S. Laal, Y. D. Sharma, H. K. Prasad, A. Murtaza, S. Singh, S. Tangri, R. Misra, and I. Nath, Proc. Natl. Acad. Sci. USA 88:1054-1058, 1991). Besides the complete sequence of the A15 gene, sequencing data of two flanking ORFs are presented. Downstream from ORF II (A15), ORF III has a high degree of similarity to the genes for tomato ATP-dependent proteases that are members of a larger class of highly conserved proteases ubiquitous among prokaryotes and eukaryotes.(ABSTRACT TRUNCATED AT 400 WORDS)

Leprosy vaccines

Leprosy is the clinical manifestation of chronic infection with Mycobacterium leprae, an intracellular parasite with a predilection for skin and nerves. Disabilities and mutilations associated with this disease, which are attributable primarily to nerve involvement, have made leprosy among the most feared and stigmatizing of all diseases. It is still widespread in the warmer regions of the globe, including southern Europe, southern USA and most of the developing countries. Though widespread, the distribution of the disease in endemic regions is sparse (a prevalence rate of 1 per 1000 is high) and predominantly rural, for reasons which are not understood, but which add to the difficulty of providing effective disease control.

Cloning and characterization of the Mycobacterium leprae putative ribosomal RNA promoter in Escherichia coli

The putative promoter region of the 16S ribosomal RNA-encoding gene (rRNA) of Mycobacterium leprae was cloned and characterized in Escherichia coli. A 932-bp HaeIII restriction fragment, containing the 5' end of the 16S rRNA gene and flanking upstream region, was cloned in front of a promoterless reporter gene in the shuttle vector, pMH109, to generate the plasmid, pYA1101. This clone exhibits promoter activity both in Gram-(E. coli) and Gram+ (Bacillus subtilis) bacteria. Sequence analysis and primer extension experiments with mRNA derived from the M. leprae clone were used to determine the structure and the location of the promoter, as well as the transcription start point in E. coli. The promoter region contains sequences that resemble the -35 and -10 consensus sequences found in many bacteria. A region located 34 bp distal to the promoter is a putative rRNA processing signal, based on sequence homology with processing signals involved in the maturation of the rRNA precursor in B. subtilis and several Mycoplasma species.

Recombinant fusion protein identified by lepromatous sera mimics native Mycobacterium leprae in T-cell responses across the leprosy spectrum

Pooled polyvalent sera from lepromatous leprosy patients were used to screen a lambda gt11 recombinant DNA expression library of Mycobacterium leprae in order to identify the relevant antigens recognized by the human immune response. Of the 300,000 phages screened, 4 clones were identified that coded for fusion proteins of the same molecular mass. The fusion protein from clone LSR2 was tested for immunoreactivity in assays using peripheral blood cells and sera from 11 laboratory personnel and 105 patients across the leprosy spectrum. LSR2 protein appears to be predominantly a T-cell antigen. It evokes similar lymphoproliferative responses as the native bacillus both at the individual level and in the leprosy spectrum as a whole. Though only 50% of patient sera with anti-M. leprae antibodies reacted with the fusion protein, the pattern of reactivity in the antibody responses was also similar for the various clinical types. The coding regions of clones LSR1 and LSR2 are identical. They show no homology with sequences stored in data banks and encode a protein of 89 amino acids with a calculated molecular mass of approximately 10 kDa.

Selection and characterization of recombinant clones that produce Mycobacterium leprae antigens recognized by antibodies in sera from household contacts of leprosy patients

A Mycobacterium leprae expression library was constructed in the vectors EX1, pEX2, and pEX3 and screened with a pool of 19 well-absorbed sera from household contacts of leprosy patients. Twelve selected recombinants that were further characterized differed clearly from recombinants selected with murine monoclonal antibodies. Whereas the monoclonal antibodies recognized mainly six recombinant antigens, the human sera from contacts reacted with a range of different recombinant antigens. None of the contact recombinant antigens was identical or related to well-characterized antigens from M. leprae or other mycobacteria selected with monoclonal antibodies, including proteins of the heat shock families. Two groups of recombinant antigens could be distinguished: one that was recognized by all sera used in the pool and one that was recognized by only a limited number of sera. These antigens, selected with sera from household contacts of previously untreated lepromatous leprosy patients, may be relevant to the immune responses during the early phase of infection with M. leprae.

Protein antigens of Mycobacterium leprae

Protein antigens of Mycobacterium leprae have been identified by screening the lambda gt11, pYA626 and pHC79::M. leprae genomic libraries with pooled sera from leprosy patients and with antiserum to M. leprae cell wall protein (CWP) aggregate. Immunological screening of the lambda gt11 library with pooled sera from 21 lepromatous (LL) leprosy patients resulted in the identification of 19 antigens that are apparently different from previously identified M. leprae antigens. Five additional antigens were identified by screening the lambda gt11 library with pooled sera from 30 borderline tuberculoid or tuberculoid patients. Four other antigens were identified by screening the lambda gt11 library with anti-CWP. Two groups of recombinant cosmids were identified by screening the pHC79 library with LL patients' sera: one group specified proteins that reacted with monoclonal antibodies (mAb) against the 65-kDa protein and against the 18-kDa protein; the other group specified a 15-kDa protein that did not react with any of the mAb that were tested. One pYA626 clone also specified a 15-kDa protein that reacted with LL patients' sera, but did not react with any mAb. Genes specifying several of these antigens have been subcloned into the Asd+ plasmid vector pYA292 and have been introduced into a delta cya delta crp delta asd Salmonella typhimurium strain to evaluate the ability of individual M. leprae proteins to elicit immune responses against M. leprae infection.