Immunogenetic analysis of human tuberculosis

Past, present and future directions in human genetic susceptibility to tuberculosis

The historical impression that tuberculosis was an inherited disorder has come full circle and substantial evidence now exists of the human genetic contribution to susceptibility to tuberculosis. This evidence has come from several whole-genome linkage scans, and numerous case-control association studies where the candidate genes were derived from the genome screens, animal models and hypotheses pertaining to the disease pathways. Although many of the associated genes have not been validated in all studies, the list of those that have been is growing, and includes NRAMP1, IFNG, NOS2A, MBL, VDR and some TLR. Certain of these genes have consistently been associated with tuberculosis in diverse populations. The future investigation of susceptibility to tuberculosis is almost certain to include genome-wide association studies, admixture mapping and the search for rare variants and epigenetic mechanisms. The genetic identification of more vulnerable individuals is expected to inform personalized treatment and perhaps vaccination strategies.

Tuberculosis

Tuberculosis is still a leading cause of death in low-income and middle-income countries, especially those of sub-Saharan Africa where tuberculosis is an epidemic because of the increased susceptibility conferred by HIV infection. The effectiveness of the Bacille Calmette Guérin (BCG) vaccine is partial, and that of treatment of latent tuberculosis is unclear in high-incidence settings. The routine diagnostic methods that are used in many parts of the world are still very similar to those used 100 years ago. Multidrug treatment, within the context of structured, directly observed therapy, is a cost-effective control strategy. Nevertheless, the duration of treatment needed reduces its effectiveness, as does the emergence of multidrug-resistant and extensively drug-resistant disease; the latter has recently become widespread. The rapid expansion of basic, clinical, and operational research, in addition to increasing knowledge of tuberculosis, is providing new diagnostic, treatment, and preventive measures. The challenge is to apply these advances to the populations most at risk. The development of a comprehensive worldwide plan to stop tuberculosis might facilitate this process by coordinating the work of health agencies. However, massive effort, political will, and resources are needed for this plan to succeed.

Frequency of DRB1–DQB1 two-locus haplotypes in tuberculosis: Preliminary report

Analysis of correlation between tuberculosis (TB) and human leukocyte antigen (HLA) in populations from Asia and Latin America has shown conflicting results. The aim of this study was to evaluate the frequency of HLA-DRB1-DQB1 two-locus haplotypes of 61 TB patients and 125 healthy volunteers in the same ethnic group in Poland. DRB1 and DQB1 alleles were determined by PCR-SSP "low-resolution" and "high-resolution" methods. Our study showed that DRB1*1601 and DQB1*0502 alleles were more frequent, whereas DQB1*0201 was rarer in TB than in controls. DRB1*16-DQB1*05, DRB1*04-DQB1*03 and DRB1*1601-DQB1*0502 haplotype were more common, and DRB1*11-DQB1*03 less frequent in TB in comparison to controls. Positive linkage disequilibrium (LD) for DRB1*01-DQB1*05, DRB1*03-DQB1*02, DRB1*11-DQB1*03, DRB1*13-DQB1*06 and DRB1*15-DQB1*06 was found in controls. A trend towards the positive LD for DRB1*01-DQB1*05, DRB1*03-DQB1*02, DRB1*11-DQB1*03, DRB1*15-DQB1*06 and DRB1*16-DQB1*05 was shown in TB. The trend towards the positive LD for DRB1*16-DQB1*05 haplotype in TB patients was not observed in the control group. It seems likely that the presence of DRB1*1601, DQB1*0502 alleles and DRB1*1601-DQB1*0502, DRB1*04-DQB1*03, DRB1*14-DQB1*05 haplotypes may be related to a higher risk of developing TB, whereas low frequency of DQB1*0201 and DRB1*11-DQB1*03 haplotype may be linked to the resistance to TB.

Genetic susceptibility to tuberculosis

Host genetic factors are important in determining susceptibility and resistance to Mycobacterium tuberculosis. The etiology of tuberculosis is complex, and several host genes have been shown to contribute to the development of clinical disease. The success of the strategies used to investigate host genetic susceptibility to mycobacterial infections can serve as a model for the investigation of host susceptibility to other infectious diseases.

Heritability analysis of cytokines as intermediate phenotypes of tuberculosis

Numerous studies have provided support for genetic susceptibility to tuberculosis (TB); however, heterogeneity in disease expression has hampered previous genetic studies. The purpose of this work was to investigate possible intermediate phenotypes for TB. A set of cytokine profiles, including antigen-stimulated whole-blood assays for interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, transforming growth factor (TGF)-beta, and the ratio of IFN to TNF, were analyzed in 177 pedigrees from a community in Uganda with a high prevalence of TB. The heritability of these variables was estimated after adjustment for covariates, and TNF-alpha, in particular, had an estimated heritability of 68%. A principal component analysis of IFN-gamma, TNF-alpha, and TGF-beta reflected the immunologic model of TB. In this analysis, the first component explained >38% of the variation in the data. This analysis illustrates the value of such intermediate phenotypes in mapping susceptibility loci for TB and demonstrates that this area deserves further research.

Susceptibility to mycobacterial infections: the importance of host genetics

There is substantial evidence that host genetic factors are important in determining susceptibility to mycobacteria. Several different techniques have been used to identify the genes involved. Studies of an inbred strain of mice with increased susceptibility to mycobacteria, salmonella and leishmania infections led to the identification of the natural resistance-associated macrophage protein gene (Nramp1). Case-control studies have confirmed the importance of the human equivalent of this gene, NRAMP1, and have also suggested that the major histocompatibility complex and vitamin-D receptor genes may be involved in determining human susceptibility to mycobacteria. Studies of individuals with the rare condition of increased susceptibility to disseminated bacille Calmette-Guerin and other atypical mycobacterial infections have identified several abnormalities in the genes encoding the interferon gamma receptor (IFNgammaR) ligand binding chain, IFNgammaR signal transduction chain, IFNgamma signal transduction and activation of transcription-1, interleukin 12 receptor beta1 subunit and interleukin 12 p40 subunit. A genome-wide linkage study has been performed to identify genes exerting a major effect on tuberculosis susceptibility in the general population. Linkages were found to markers on chromosomes 15 and X. Studies to identify the genes responsible are in progress.

Genetic dissection of immunity to mycobacteria: the human model

Humans are exposed to a variety of environmental mycobacteria (EM), and most children are inoculated with live Bacille Calmette-Guérin (BCG) vaccine. In addition, most of the world's population is occasionally exposed to human-borne mycobacterial species, which are less abundant but more virulent. Although rarely pathogenic, mildly virulent mycobacteria, including BCG and most EM, may cause a variety of clinical diseases. Mycobacterium tuberculosis, M. leprae, and EM M. ulcerans are more virulent, causing tuberculosis, leprosy, and Buruli ulcer, respectively. Remarkably, only a minority of individuals develop clinical disease, even if infected with virulent mycobacteria. The interindividual variability of clinical outcome is thought to result in part from variability in the human genes that control host defense. In this well-defined microbiological and clinical context, the principles of mouse immunology and the methods of human genetics can be combined to facilitate the genetic dissection of immunity to mycobacteria. The natural infections are unique to the human model, not being found in any of the animal models of experimental infection. We review current genetic knowledge concerning the simple and complex inheritance of predisposition to mycobacterial diseases in humans. Rare patients with Mendelian disorders have been found to be vulnerable to BCG, a few EM, and M. tuberculosis. Most cases of presumed Mendelian susceptibility to these and other mycobacterial species remain unexplained. In the general population leprosy and tuberculosis have been shown to be associated with certain human genetic polymorphisms and linked to certain chromosomal regions. The causal vulnerability genes themselves have yet to be identified and their pathogenic alleles immunologically validated. The studies carried out to date have been fruitful, initiating the genetic dissection of protective immunity against a variety of mycobacterial species in natural conditions of infection. The human model has potential uses beyond the study of mycobacterial infections and may well become a model of choice for the investigation of immunity to infectious agents.

Molecular subtypes of the HLA-DR antigens in pulmonary tuberculosis

OBJECTIVE

The aim of this study was to analyze association between HLA-DRB1 alleles and pulmonary tuberculosis (PTB) in the Polish population.

METHODS

The HLA-DRB1 typing was performed using sequence-specific amplification (polymerase chain reaction with sequence specific primer [PCR-SSP] in 31 patients and 58 healthy volunteers. The DRB1 primers were supplied by DYNAL in the standard kit DYNAL DR "low-resolution"-SSP.

RESULTS

The study showed that the DRB1*16 alleles frequency was higher in patients with PTB than in the tested group of healthy controls (P < 0.01). When HLA-DR2 alleles were combined (i.e., the DRB1*15 with DRB1*16 alleles), their frequency was comparable with that in the healthy individuals. The highest relative risk (RR) of tuberculosis was associated with DRB1*16 alleles (RR = 9.7). When HLA-DR6 alleles were combined (i.e., the DRB1*13 with DRB1*14 alleles), only a trend for higher frequency in patients with PTB was found. Frequency of DRB1*13 alleles of HLA-DR6 was significantly lower in PTB than in the healthy individuals (P < 0.001; RR = 0.04).

CONCLUSIONS

Results suggest that the presence of HLA-DRB1*16 alleles may increase the risk of development of PTB, whereas HLA-DRB1*13 alleles may be resistant to tuberculosis.

Influence of HLA-DR antigens on lymphocyte response to Mycobacterium tuberculosis culture filtrate antigens and mitogens in pulmonary tuberculosis

SETTING

Influence of HLA-DR antigens and lymphocyte responses in pulmonary TB patients.

OBJECTIVE

To elucidate the role of HLA-DR genes/gene products on lymphocyte responses to Mycobacterium tuberculosis antigens and mitogens, the present study was carried out in pulmonary tuberculosis during active and cured stage of the disease.

DESIGN

Serological determination of HLA-DR antigens was carried out in 50 active TB patients, 44 cured TB patients and 58 normal healthy control subjects. The influence of HLA-DR antigens on peripheral blood lymphocyte responses to M. tuberculosis culture filtrate antigens and mitogens such as phytohaemagglutinin (PHA) and concanavalin-A (Con-A) was studied in the patients as well as normal healthy control subjects.

RESULTS

Of all the DR antigens studied, patients (active TB and cured TB) with DR2 antigen showed an increased lymphocyte response (stimulation index) to a higher dose of antigenic (10 micrograms/ml) stimulation. A significantly lower lymphocyte response to antigen and mitogens was seen in HLA-DR3 positive normal healthy subjects than non-DR3 (DR3 negative) subjects.

CONCLUSION

The present study suggests that HLA-DR genes/gene products may be playing an immunoregulatory role in eliciting an immune response against M. tuberculosis antigens and mitogens induced lymphocyte response in pulmonary TB patients and normal healthy subjects.

Associations of HLA-DRB1, DQB1 and DPB1 alleles with pulmonary tuberculosis in south India

SETTING

Tuberculosis is endemic in south India: sputum positive pulmonary tuberculosis is predisposed by HLA-DR2 in south India and few other populations of the world.

OBJECTIVE

To study HLA-DRB1, DQB1, DQA1 and DPB1 allelic polymorphism in pulmonary tuberculosis patients and endemic controls from south India.

DESIGN

One hundred and twenty-six, sputum positive pulmonary tuberculosis patients and 87, endemic controls, from Madurai were studied for MHC class II allelic polymorphism by PCR-SSOP method. XI IHWC primers and probes and non-radioactive probing methods were employed.

RESULTS

HLA DRB1*1501 and DQB1*0601 predisposed for pulmonary tuberculosis (DRB1*1501: odds ratio (OR) = 2.68, 95% confidence interval (CI) = 1.30-5.89, P value (P) = 0.013, aetiological fraction (EF) = 0.17; DQB1*0601: OR = 2.32, CI = 1.29-4.27, P = 0.008, EF = 0.26). Haplotype DRB1*1501-DQB1*0601 was higher in patients (1324 per 10,000, X2 = 27.07) than controls (F = 404/10,000, X2 = 8.84). In a subset of 63 caste matched samples, DPB1*04 was preventive (OR = 0.45, CI = 0.21-0.95, P = 0.036, PF = 0.26): the distributions of DRB1*1501-DQB1*0601-DPB1*04 phenotypes were different between patients and controls (P = 0.0092). These alleles were predominant in patients and controls of T5SU caste.

CONCLUSION

HLA-DRB1*1501 and DQB1*0601 predisposed to sputum positive pulmonary tuberculosis, and DPB1*04 was preventive and epistatic to this risk. Caste T5SU is an ideal model to study immunology of tuberculosis.

Mannose-binding protein B allele confers protection against tuberculous meningitis

Inhalation is the principal mode of entry for Mycobacterium tuberculosis in humans. Primary infection is usually restricted to the lungs and contiguous lymph nodes. In a subset of infected individuals, predominantly children, the infection is spread hematogenously to the meninges. The host factors that influence the development of tuberculous meningitis have not been well elucidated. The mannose-binding protein (MBP), a serum protein, is considered as an "ante-antibody." MBP has been shown to bind mycobacteria and acts as an opsonin in vitro. Although MBP plays a role in first-line host defense, it may under certain circumstances be deleterious to the host. In tuberculosis (TB), MBP may assist the spread of this intracellular pathogen. Therefore, we hypothesized that MBP genotypes that result in a phenotype of low MBP levels might be protective. We studied a well-defined South African population in which TB has reached epidemic levels. We found that the MBP B allele (G54D), which disrupts the collagen region of the protein and results in low MBP levels, was found in 22 of 79 (28%) of the TB-negative controls from the same community, compared with 12 of 91 (13%) of the patients with pulmonary TB (p < 0.017), and 5 of 64 (8%) of patients with tuberculous meningitis (p < 0.002). In addition, we found significantly lower serum MBP concentrations in TB-negative controls compared with postacute phase, fully recovered TB patients (p < 0.004). These findings suggest that the MBP B allele affords protection against tuberculous meningitis.

Examining a paradox in the pathogenesis of human pulmonary tuberculosis: immune activation and suppression/anergy

Protective immunity against Mycobacterium tuberculosis (MTB) in animal models is based on cell-mediated immunity (CMI), involving bi-directional interactions between T cells and cells of the monocyte/macrophage (MO/MA) lineage. Key factors include MO-derived interleukin (IL)-12 and tumor necrosis factor (TNF)-alpha as well as T cell derived IL-2 and interferon (IFN)-gamma. These cytokines appear particularly crucial in the induction of MA-mediated elimination of mycobacteria. Several lines of evidence indicate that similar mechanisms are operating in humans. During active pulmonary tuberculosis (PTB), signs of both immune depression and immune activation are concomitantly present. Decreased tuberculin skin test reactivity in vivo and deficient IFN-gamma production by MTB-stimulated mononuclear cells in vitro are observed. On the other hand, the serum levels of several cytokines, including TNF, and other inflammatory mediators are increased and circulating MO and T cell show phenotypic and functional evidence of in vivo activation. In this review, we will discuss the evidence for three models, which could explain this apparent paradox: 1. Stimulation of the T cell-suppressive function from MO/MA; 2. Intrinsic T cell refractoriness, possibly associated with tendency to apoptosis (programmed cell death), and 3. Compartmentalization and redistribution of immune responses to the site of disease. The opportunistic behavior of MTB during human immunodeficiency virus (HIV) infection can be explained by suppression of type-1 responses at the level of antigen-presenting cells, CD4 T cells and effector macrophages. The ominous prognostic significance of intercurrent PTB during HIV infection seems primarily due to prolonged activation of HIV replication in macrophages. Supportive immune therapy during PTB could aim at correcting the type-1 deficiency either by IFN-gamma inducers (e.g. IL-12, IL-18) or by neutralizing the suppressive cytokines transforming growth factor beta (TGF-beta) and IL-10. Alternatively, inflammatory over-activity could be reduced by neutralizing TNF. Finally, anti-apoptotic therapies (e.g. IL-15) might be considered.

Human leukocyte antigens in tuberculosis and leprosy

Human mycobacterial infections are characterized by a spectrum of clinical and immunological manifestations. Specific human leukocyte antigen (HLA) factors are associated with the subtypes of leprosy that develop and the course of tuberculosis after infection. The identification of protective mycobacterial antigens presented by a broad variety of HLA molecules will have important implications for the design of vaccines.

Influence of HLA-DR and -DO phenotypes on tuberculin reactive status in pulmonary tuberculosis patients

SETTING

HLA and tuberculin status in pulmonary tuberculosis patients. Tuberculosis Research Centre, Indian Council of Medical Research, Madras, India.

OBJECTIVE

To elucidate the role of HLA-class-II genes/gene products on tuberculin reactivity in pulmonary tuberculosis patients.

DESIGN

Serological determination of HLA-DR and -DQ antigens was carried out in 62 healthy control subjects and 146 pulmonary tuberculosis patients. The tuberculin reaction pattern of pulmonary tuberculosis patients to PPD was studied and the role of HLA-DR and -DQ antigens (class-II gene products) on tuberculin reaction was analysed.

RESULTS

HLA-DR and -DQ antigens did not influence high, medium and low tuberculin reaction dramatically in active pulmonary tuberculosis patients. However, a heterozygous combination of various HLA-DR antigens influenced the tuberculin reaction.

CONCLUSION

The HLA-genetic make up (heterozygous combination) of the individual may influence the tuberculin reaction pattern in pulmonary tuberculosis.

Quantitation of soluble HLA class I heterodimers and beta 2-microglobulin in patients with active pulmonary tuberculosis

Beta 2m serum levels have been shown to be increased in patients with tuberculosis and HIV infection. We determined the stability of beta 2m and of sHLA-I dimers in serum, and then determined the levels of both molecules in 60 non-HIV-infected patients with active pulmonary tuberculosis and in 55 adult controls. The levels of sHLA-I in samples kept at room temperature declined by 8% at 30 minutes, 16% at 60 minutes, and 36% at 120 minutes. Beta 2m levels remained stable at all times tested. Mean sHLA-I levels were 0.99 +/- 0.16 micrograms/ml in controls and 1.34 +/- 0.11 micrograms/ml in patients with tuberculosis (P < 0.0001). Beta 2m levels were 1.23 +/- 0.26 micrograms/ml in controls and 2.26 +/- 0.64 micrograms/ml in patients with tuberculosis (P < 0.0001). All patients with tuberculosis had elevation of sHLA-I and/or beta 2m above 1 standard deviation of normal values. However, there was no correlation between sHLA-I and beta 2m levels in individual samples. Evaluation of sHLA-I holds the promise of further understanding of the biology and genetic regulation of the immune response to mycobacterial infection.

Tuberculin reactivity after newborn BCG immunization in mono- and dizygotic twins

SETTING

Studies showing significantly higher concordance of tuberculosis among monozygotic twins than dizygotic twins have provided support for genetically determined susceptibility to tuberculosis.

OBJECTIVE

We wished to explore whether the development of delayed type hypersensitivity to tuberculin after newborn BCG immunization of twins suggested genetic regulation of the response to BCG in humans.

DESIGN

Our study population consisted of 17 monozygotic twin pairs, 18 dizygotic twin pairs, and 64 single infants 3-34 months of age from Santiago, Chile. All had a BCG scar and were tuberculin tested by one trained nurse.

RESULTS

The mean birth weight of both groups of twins was significantly lower than that of singletons and the percentage of individuals who failed to respond to tuberculin was approximately twice as high in twins as in singletons. After adjustment for birth weight and age by regression analysis, it was found that the distribution of tuberculin reactivity in both monozygotic and dizygotic twins was not significantly different from that of singletons. Both twin pair correlations is adjusted tuberculin reactivity were significantly greater than zero (P < 0.01) and led to a heritability estimate of 0.28. However, the monozygotic twin correlation was not significantly larger than the dizygotic twin correlation so that heritability is poorly estimated.

CONCLUSION

These results are consistent with a genetic regulation of the response to newborn BCG immunization in humans by a mechanism capable of producing similar responses in identical and nonidentical twins alike.

An RFLP map for 2q33-q37 from multicase mycobacterial and leishmanial disease families: no evidence for an Lsh/Ity/Bcg gene homologue influencing susceptibility to leprosy

The mycobacterial diseases leprosy and tuberculosis (TB) and the leishmaniases are characterized by a wide spectrum of disease phenotypes, and by the fact that the majority of individuals exposed to the causative organisms Mycobacterium leprae, M. tuberculosis and Leishmania sp. become infected but do not present with clinical disease. In order to determine whether a human homologue to the murine macrophage resistance gene Lsh/Ity/Bcg influences susceptibility to human disease, multicase families for all three diseases have been collected, and linkage analysis performed using a panel of markers in the region of human chromosome 2q33-q37 known to be conserved with the Lsh/Ity/Bcg-containing region of murine chromosome 1. Because of the paucity of available polymorphic markers/linkage information for 2q33-q37, data from 35 multicase leprosy, TB and visceral leishmaniasis families (310 individuals) were first pooled to produce a detailed RFLP map of the region. Peak LOD scores well in excess of 3 were observed for linkage between adjacent pairs of a more proximal (2q33-q35) set of markers CRYGP1, MAP2, FN1, TNP1, VIL1 and DES, and between adjacent pairs of a more distal (2q35-q37) set COL6A3, D2S55 and D2S3. These peak LOD scores and the corresponding values for theta were used in the MAP92 program to generate a multiple two-point map with gene order/map intervals (cM) of: CRYGP1-4.65-MAP2-3.45-FN1-5.95-TNP1-3.41-VIL1-3. 01- DES-20.14-COL6A-10.91-D2S55-3.67-D2S3. Although local support for the placement of loci in this order was weak (LOD < 2, except for DES-COL6A3 where LOD = 6.02), the map is consistent with the gene order for those loci (Cryg, Fn-1, Tp-1, Vil, Des, Col6a3) previously mapped in the mouse. Data from 17 multicase leprosy families (149 individuals) were further analysed for linkage between a putative disease susceptibility locus (DSL) controlling susceptibility to leprosy per se and each of the marker loci. Assuming 100% penetrance for the susceptibility allele, no positive LOD score was obtained for linkage between the DSL and any of the marker genes. Instead, the data provide convincing evidence (LOD scores < -2) that a DSL does not fall within 10-20 cM of CRYGP1, MAP2, TNP1, VIL1, DES or D2S55, or within 5-10 cM of FN1, COL6A3 or D2S3. This effectively excludes a putative DSL controlling susceptibility to leprosy per se from the entire region 2q33-q37.(ABSTRACT TRUNCATED AT 400 WORDS)

Repeated tuberculin testing in patients with active pulmonary tuberculosis

OBJECTIVE

The proportion of tuberculin reactors in a population and the intensity of tuberculin reactions have been shown to increase with increasing exposure to mycobacterial infection, eg, repeated BCG immunization. These observations suggested that tuberculin reactivity would become uniformly high in individuals with a high mycobacterial load who did not have a known cause of anergy. Since tuberculin reactivity has been measured to evaluate the possible genetic regulation of responses to mycobacteria in humans, it is important to study its behavior under conditions of ongoing, maximal exposure to mycobacteria. In the present study, we determined the mean size of tuberculin reactivity in BCG-immunized and unimmunized patients with pulmonary tuberculosis of recent onset, and the stability of tuberculin reactions during and after treatment of pulmonary tuberculosis.

METHOD

Serial tuberculin testing was performed on patients with newly diagnosed active pulmonary tuberculosis diagnosed over a period of 2 years at the National Institute for Respiratory Diseases in Santiago, Chile. The first tuberculin test was performed at the time of diagnosis in 58 patients. Repeated tuberculin testing was performed 2 weeks later in 15 patients with initial reaction sizes < 15 mm. Four additional tuberculin tests were performed, one each at 3-months intervals in 42 patients regardless of the size of the initial tuberculin reaction.

RESULTS

Tuberculin reactions at entry had a unimodal distribution in patients both with and without BCG scars (14.8 +/- 5.0 mm and 16.5 +/- 5.2 mm, respectively). A second tuberculin test in patients with initial reaction sizes < 15 mm showed a moderate, statistically significant increase in the mean reaction size (PPD1: 10.1 +/- 3.2 mm; PPD2: 11.9 +/- 4.8 mm). Repeated tuberculin testing over 1 year revealed no significant changes in reaction size. The mean reaction sizes were 15.8 +/- 5.0 mm at entry, 15.5 +/- 5.4 mm at 3 months, 17.2 +/- 5.2 mm at 6 months, 17.0 +/- 5.1 mm at 9 months, and 16.7 +/- 54 mm at 12 months. The standard deviation of a random observation within patients was 5.3 mm. The largest variations due to increased reactivity after 6 months of treatment were observed in patients with reaction < 15 mm at entry compared with hyperergic patients, and in BCG-immunized patients compared to unimmunized patients.

CONCLUSIONS

In the presence of an ongoing mycobacterial infection, patients without anergizing conditions express a tuberculin reactivity that is relatively constant during and after treatment of pulmonary tuberculosis. The size and stability of the reactions seem to be determined by individual conditions that include the tuberculin reactivity at the time of diagnosis and the BCG immunization status.

T cell repertoire in tuberculosis: selective anergy to an immunodominant epitope of the 38-kDa antigen in patients with active disease

It is generally accepted that both host protection and pathogenic reactions in tuberculosis are mediated by T lymphocytes. However, little is known about the structures and discreet functions of epitopes stimulating the immune response. In this study, proliferative responses of blood T lymphocytes to synthetic peptides derived from the sequence of the 38-kDa antigen from Mycobacterium tuberculosis have been investigated in 41 healthy individuals and in 36 patients with active tuberculosis. Of the healthy purified protein derivative (PPD)-positive donors, 90% responded to a permissively recognized peptide, 38.G (residues 350-359), located at the carboxy terminus of the molecule. Four other permissively recognized epitopes of this molecule (38.A, 38.I, 38.E, 38.K) were stimulatory for more than 50% of healthy PPD-positive individuals. Patients with lymphatic tuberculosis responded to these peptides in a similar manner. In contrast, we observed a selective anergy to stimulation with peptide 38.G in the majority of patients with pulmonary (11% responders) and nonlymphatic extrapulmonary tuberculosis (25% responders). The lack of responsiveness to 38.G was epitope specific since the degree of responsiveness to the other four permissively recognized peptide epitopes was similar for patients and PPD-positive controls. Using the PEPSCAN technology and truncated peptides, the core epitope of 38.G was localized to a peptide 10 amino acids long (HFQPLPPAVV). This minimal structure was capable of inducing a proliferative response in all healthy 38.G responders tested. The mechanisms influencing this epitope-specific anergy in patients could give new insights into the immunopathogenesis of tuberculosis.

Repertoires of antibodies to culture filtrate antigens in different mouse strains infected with Mycobacterium bovis BCG

Two susceptible (Bcgs) mouse strains, BALB/c and C57BL/6, were compared by Western blot (immunoblot) analysis for their immunoglobulin G response to 14-day-old BCG culture filtrate (CF) following intravenous infection with live Mycobacterium bovis BCG. The two strains demonstrated a completely different antibody repertoire. BALB/c antibodies were directed against a wide range of CF antigens between 20 and about 100 kilodaltons (kDa), with a preferential recognition of the 65-kDa heat shock protein and the 32-kDa fibronectin-binding protein. C57BL/6 sera, on the other hand, showed a much more restricted antibody pattern, almost exclusively directed against three antigens with estimated molecular sizes of 37, 38, and 40 kDa. Whereas the 37- and 38-kDa antigens were also recognized by BALB/c mice, the 40-kDa antigen was very intensely stained by C57BL/6 sera only. F1 mice had the restricted antibody pattern of C57BL/6 after one injection of BCG and had a hybrid BALB/c-C57BL/6 phenotype following a boost injection of BCG 2 months after the initial infection. Analysis of seven recombinant inbred strains derived from the BALB/c x C57BL/6 cross and of congenic mice differing in major histocompatibility complex-coding chromosome 17 fragments suggests that a gene in the K-IA region of the H-2 locus is associated with the preferential recognition of certain CF antigens. Inoculation with the same dose of killed BCG failed to elicit an antibody response to these filtrate antigens.