Insulin resistance, and not β-cell impairment, mediates association between Mycobacterium tuberculosis sensitization and type II diabetes mellitus among US adults

Type 2 diabetes mellitus (T2DM) may be a long-term sequela of infection with Mycobacterium tuberculosis (M.tb) by mechanisms that remain to be fully explained. We evaluated association between M.tb sensitization and T2DM among U.S adults and, via formal mediation analysis, the extent to which this association is mediated by insulin resistance and/or β-cell failure. These evaluations accounted for demographic, socio-economic, behavioral and clinical characteristics. T2DM was assessed by fasting plasma glucose, 2-hour oral glucose tolerance testing and HbA1c; homoeostasis model assessment 2 (HOMA2) was used to estimate β-cell dysfunction (HOMA2-B) and insulin resistance (HOMA2-IR); while M.tb sensitization status was ascertained by tuberculin skin testing (TST). Exposure to M.tb was associated with increased risk for T2DM, likely driven by an increase in insulin resistance. Definitive prospective studies examining incident T2DM following tuberculosis are warranted.

Research in Context

What is already known about this subject?: Accumulating evidence suggests that pre-diabetes and new-onset type 2 diabetes mellitus (T2DM) may be a long-term complication of exposure to Mycobacterium tuberculosis ( M.tb ) via mechanisms that remain to be unraveled What is the key question?: To what extent do insulin resistance and β-cell failure mediate the association between M.tb sensitization with T2DM among US adults? What are the new findings?: M.tb sensitization is characterized by distinct glucose metabolic disturbances manifesting as increased risk of T2DM and isolated impaired fasting glucose (IFG) Insulin resistance, and not β-cell impairment, likely independently mediate the observed diabetogenic effects of M.tb sensitization How might this impact on clinical and/or public health practice in the foreseeable future?: If corroborated by prospective studies, both TB programs and individual clinical care must incorporate monitoring of serum glucose and long-term metabolic outcomesThis will be particularly urgent in sub-Saharan Africa and South-East Asia where scarce health resources coincide with overlapping endemic TB and epidemic T2DM.

Elevated plasma matrix metalloproteinases associate with Mycobacterium tuberculosis blood stream infection and mortality in HIV-associated tuberculosis

Mortality from HIV-associated tuberculosis (HIV-TB) is high, particularly among hospitalised patients. In 433 people living with HIV admitted to hospital with symptoms of TB, we investigated plasma matrix metalloproteinases (MMP) and matrix-derived biomarkers in relation to TB diagnosis, mortality and Mycobacterium tuberculosis (Mtb) blood stream infection (BSI). Compared to other diagnoses, MMP-8 was elevated in confirmed TB and in Mtb-BSI, positively correlating with extracellular matrix breakdown products. Baseline MMP-3, -7, -8, -10 and procollagen III N-terminal propeptide (PIIINP) associated with Mtb-BSI and 12-week mortality. These findings implicate MMP dysregulation in pathophysiology of advanced HIV-TB and support MMP inhibition as a host-directed therapeutic strategy for HIV-TB.

Interferon release does not add discriminatory value to smear-negative HIV-tuberculosis algorithms

Clinical algorithms for evaluating HIV-infected individuals for tuberculosis (TB) prior to isoniazid preventive therapy (IPT) perform poorly, and interferon-γ release assays (IGRAs) have moderate accuracy for active TB. It is unclear whether, when used as adjunct tests, IGRAs add any clinical discriminatory value for active TB diagnosis in the pre-IPT assessment. 779 sputum smear-negative HIV-infected persons, established on or about to commence combined antiretroviral therapy (ART), were screened for TB prior to IPT. Stepwise multivariable logistic regression was used to develop clinical prediction models. The discriminatory ability was assessed by receiver operator characteristic area under the curve (AUC). QuantiFERON-TB Gold in-tube (QFT-GIT) was evaluated. The prevalence of smear-negative TB by culture was 6.4% (95% CI 4.9-8.4%). Used alone, QFT-GIT and the tuberculin skin test (TST) had comparable performance; the post-test probability of disease based on single negative tests was 3-4%. In a multivariable model, the QFT-GIT test did not improve the ability of a clinical algorithm, which included not taking ART, weight <60 kg, no prior history of TB, any one positive TB symptom/sign (cough ≥ 2 weeks) and CD4+ count <250 cells per mm(3), to discriminate smear-negative culture-positive and -negative TB (72% to 74%; AUC comparison p=0.33). The TST marginally improved the discriminatory ability of the clinical model (to 77%, AUC comparison p=0.04). QFT-GIT does not improve the discriminatory ability of current TB screening clinical algorithms used to evaluate HIV-infected individuals for TB ahead of preventive therapy. Evaluation of new TB diagnostics for clinical relevance should follow a multivariable process that goes beyond test accuracy.

Hypercytokinaemia accompanies HIV-tuberculosis immune reconstitution inflammatory syndrome

Increased access to combination antiretroviral therapy in areas co-endemic for tuberculosis (TB) and HIV-1 infection is associated with an increased incidence of immune reconstitution inflammatory syndrome (TB-IRIS) whose cause is poorly understood. A case-control analysis of pro- and anti-inflammatory cytokines in TB-IRIS patients sampled at clinical presentation, and similar control patients with HIV-TB prescribed combined antiretroviral therapy who did not develop TB-IRIS. Peripheral blood mononuclear cells were cultured in the presence or absence of heat-killed Mycobacterium tuberculosis for 6 and 24 h. Stimulation with M. tuberculosis increased the abundance of many cytokine transcripts with interleukin (IL)-1β, IL-5, IL-6, IL-10, IL-13, IL-17A, interferon (IFN)-γ, granulocyte-macrophage colony-stimulating factor (GM-CSF) and tumour necrosis factor (TNF) being greater in stimulated TB-IRIS cultures. Analysis of the corresponding proteins in culture supernatants, revealed increased IL-1β, IL-2, IL-6, IL-8, IL-10, IL-12p40, IFN-γ, GM-CSF and TNF in TB-IRIS cultures. In serum, higher concentrations of TNF, IL-6, and IFN-γ were observed in TB-IRIS patients. Serum IL-6 and TNF decreased during prednisone therapy in TB-IRIS patients. These data suggest that cytokine release contributes to pathology in TB-IRIS. IL-6 and TNF were consistently elevated and decreased in serum during corticosteroid therapy. Specific blockade of these cytokines may be rational approach to immunomodulation in TB-IRIS.

Enhanced diagnosis of HIV-1-associated tuberculosis by relating T-SPOT.TB and CD4 counts

The sensitivity of the tuberculin skin test is impaired in HIV-1-infected persons. Enzyme-linked immunospot-based detection of immune sensitisation may be less affected. Furthermore, the quantitative response can be related to the CD4 count, potentially improving specificity for active disease. The T-SPOT.TB assay was performed on HIV-1-infected participants, 85 with active tuberculosis (TB) and 81 healthy patients (non-TB). The ratio of the sum of the 6-kDa early secretory antigenic target and culture filtrate protein 10 response to the CD4 count (spot-forming cell (SFC)/CD4) was calculated. Using the manufacturer's guidelines, active TB was diagnosed with 76% sensitivity and 53% specificity. Using an SFC/CD4 ratio of 0.12, sensitivity (80%) and specificity (62%) improved. The quantitative T-cell response increased with increasing smear-positivity in the active TB group (p = 0.0008). In the non-TB group, the proportion of persons scored positive by T-SPOT.TB assay was lower in the group with a CD4 count of <200 cells·mm(-3) (p = 0.029). The ratio of the summed T-cell response to CD4 count improved the diagnostic accuracy of the T-SPOT.TB assay in HIV-1-infected persons, and a ratio of SFC/CD4 of >0.12 should prompt investigation for active disease. A strong association between the degree of sputum positivity and T-SPOT.TB score was found. The sensitivity of the T-SPOT.TB assay in active disease may be less impaired by advanced immunosuppression.

Association between Gc genotype and susceptibility to TB is dependent on vitamin D status

Group-specific component (Gc) variants of vitamin D binding protein differ in their affinity for vitamin D metabolites that modulate antimycobacterial immunity. We conducted studies to determine whether Gc genotype associates with susceptibility to tuberculosis (TB). The following subjects were recruited into case-control studies: in the UK, 123 adult TB patients and 140 controls, all of Gujarati Asian ethnic origin; in Brazil, 130 adult TB patients and 78 controls; and in South Africa, 281 children with TB and 182 controls. Gc genotypes were determined and their frequency was compared between cases versus controls. Serum 25-hydroxyvitamin D (25(OH)D) concentrations were obtained retrospectively for 139 Gujarati Asians, and case-control analysis was stratified by vitamin D status. Interferon (IFN)-gamma release assays were also performed on 36 Gujarati Asian TB contacts. The Gc2/2 genotype was strongly associated with susceptibility to active TB in Gujarati Asians, compared with Gc1/1 genotype (OR 2.81, 95% CI 1.19-6.66; p = 0.009). This association was preserved if serum 25(OH)D was <20 nmol.L(-1) (p = 0.01) but not if serum 25(OH)D was > or =20 nmol.L(-1) (p = 0.36). Carriage of the Gc2 allele was associated with increased PPD of tuberculin-stimulated IFN-gamma release in Gujarati Asian TB contacts (p = 0.02). No association between Gc genotype and susceptibility to TB was observed in other ethnic groups studied.

Responses of feline medial medullary reticular formation neurons with projections to the C5–C6 ventral horn to vestibular stimulation

Prior studies have shown that the vestibular system contributes to adjusting respiratory muscle activity during changes in posture, and have suggested that portions of the medial medullary reticular formation (MRF) participate in generating vestibulo-respiratory responses. However, there was previously no direct evidence to demonstrate that cells in the MRF relay vestibular signals monosynaptically to respiratory motoneurons. The present study tested the hypothesis that the firing of MRF neurons whose axons could be antidromically activated from the vicinity of diaphragm motoneurons was modulated by whole-body rotations in vertical planes that stimulated vestibular receptors, as well as by electrical current pulses delivered to the vestibular nerve. In total, 171 MRF neurons that projected to the C5-C6 ventral horn were studied; they had a conduction velocity of 34+/-15 (standard deviation) m/sec. Most (135/171 or 79%) of these MRF neurons lacked spontaneous firing. Of the subpopulation of units with spontaneous discharges, only 3 of 20 cells responded to vertical rotations up to 10 degrees in amplitude, whereas the activity of 8 of 14 neurons was affected by electrical stimulation of the vestibular nerve. These data support the hypothesis that the MRF participates in generating vestibulo-respiratory responses, but also suggest that some neurons in this region have other functions.

Effects of postural changes and vestibular lesions on genioglossal muscle activity in conscious cats

Previous studies in humans showed that genioglossal muscle activity is higher when individuals are supine than when they are upright, and prior experiments in anesthetized or decerebrate animals suggested that vestibular inputs might participate in triggering these alterations in muscle firing. The present study determined the effects of whole body tilts in the pitch (nose-up) plane on genioglossal activity in a conscious feline model and compared these responses with those generated by roll (ear-down) tilts. We also ascertained the effects of a bilateral vestibular neurectomy on the alterations in genioglossal activity elicited by changes in body position. Both pitch and roll body tilts produced modifications in muscle firing that were dependent on the amplitude of the rotation; however, the relative effects of ear-down and nose-up tilts on genioglossal activity were variable from animal to animal. The response variability observed might reflect the fact that genioglossus has a complex organization and participates in a variety of tongue movements; in each animal, electromyographic recordings presumably sampled the firing of different proportions of fibers in the various compartments and subcompartments of the muscle. Furthermore, removal of labyrinthine inputs resulted in alterations in genioglossal responses to postural changes that persisted until recordings were discontinued approximately 1 mo later, demonstrating that the vestibular system participates in regulating the muscle's activity. Peripheral vestibular lesions were subsequently demonstrated to be complete through the postmortem inspection of temporal bone sections or by observing that vestibular nucleus neurons did not respond to rotations in vertical planes.

Direct ex vivo analysis of antigen-specific IFN-gamma-secreting CD4 T cells in Mycobacterium tuberculosis-infected individuals: associations with clinical disease state and effect of treatment

The wide spectrum of clinical outcomes following infection with Mycobacterium tuberculosis is largely determined by the host immune response; therefore, we studied several clinically defined groups of individuals (n = 120) that differ in their ability to contain the bacillus. To quantitate M. tuberculosis-specific T cells directly ex vivo, we enumerated IFN-gamma-secreting CD4 T cells specific for ESAT-6, a secreted Ag that is highly specific for M. tuberculosis, and a target of protective immune responses in animal models. We found that frequencies of circulating ESAT-6 peptide-specific IFN-gamma-secreting CD4 T cells were higher in latently infected healthy contacts and subjects with minimal disease and low bacterial burdens than in patients with culture-positive active pulmonary tuberculosis (p = 0.009 and p = 0.002, respectively). Importantly, the frequency of these Ag-specific CD4 T cells fell progressively in all groups with treatment (p = 0.005), suggesting that the lower responses in patients with more extensive disease were not due to tuberculosis-induced immune suppression. This population of M. tuberculosis Ag-specific Th1-type CD4 T cells appears to correlate with clinical phenotype and declines during successful therapy; these features are consistent with a role for these T cells in the containment of M. tuberculosis in vivo. Such findings may assist in the design and evaluation of novel tuberculosis vaccine candidates.

Enhanced contact tracing and spatial tracking of Mycobacterium tuberculosis infection by enumeration of antigen-specific T cells

BACKGROUND

Identification of individuals latently infected with Mycobacterium tuberculosis is an important part of tuberculosis control. The current method, the tuberculin skin test (TST), has poor specificity because of the antigenic cross-reactivity of purified protein derivative (PPD) with M bovis BCG vaccine and environmental mycobacteria. ESAT-6 is a secreted antigen that is highly specific for M tuberculosis complex, but is absent from M bovis BCG. With an enzyme-linked immunospot (ELISPOT) assay for interferon gamma, we have identified ESAT-6-specific T cells as an accurate marker of M tuberculosis infection.

METHODS

We did a prospective, masked study of 50 healthy contacts, with varying but well defined degrees of exposure to M tuberculosis, who attended an urban contact-tracing clinic. We assessed and compared the efficacy of our assay and TST for detection of symptomless infected individuals by correlation of test results with the degree of exposure to an infectious index case.

FINDINGS

The ESAT-6 ELISPOT assay results had a strong positive relation with increasing intensity of exposure (odds ratio=9.0 per unit increase in level of exposure [95% CI 2.6--31.6], p=0.001), whereas TST results had a weaker relation with exposure (1.9 [1.0--3.5], p=0.05). By contrast, ELISPOT results were not correlated with BCG vaccination status (p=0.7), whereas TST results were significantly more likely to be positive in BCG-vaccinated contacts (12.1 [1.3--115.7], p=0.03).

INTERPRETATION

This new antigen-specific T cell-based assay could allow more accurate identification of symptom-free individuals recently exposed to M tuberculosis, and thereby help to improve tuberculosis control.

An increase in expression of a Mycobacterium tuberculosis mycolyl transferase gene (fbpB) occurs early after infection of human monocytes

Changes in the mRNA levels of two Mycobacterium tuberculosis genes (fbpB known as antigen 85B, and hspX known as Acr) were studied in infected human monocytes. Antigen 85B is an enzyme involved in cell wall biosynthesis and is also a major target of the immune response. Acr is a stress protein believed to be involved in the bacillary response to adverse conditions and in non-replicating persistence. During the first 24 h of intracellular infection, the intramonocyte 85B mRNA level increased 54-fold (P = 0.00001) and 14.6 times in comparison with the 16S ribosomal rRNA. In contrast, the Acr mRNA fell 14.3 times. Although monocyte cytokine production was very variable, the 24 h secretion of tumour necrosis factor (TNF)-alpha correlated with the 85B-16S RNA ratio at 24 h (r = 0.77, Pcorr < 0.01). Furthermore, the addition of exogenous TNF-alpha to cultures was associated with a twofold increase in the 85B-16S ratio and, conversely, neutralization of endogenous TNF-alpha reduced the ratio. As antigen 85B also induces TNF-alpha, the positive feedback implied by our findings suggests a previously unsuspected role for this protein in the immunopathogenesis of tuberculosis.

Enumeration of T cells specific for RD1-encoded antigens suggests a high prevalence of latent Mycobacterium tuberculosis infection in healthy urban Indians

Knowledge of the prevalence of latent Mycobacterium tuberculosis infection is crucial for effective tuberculosis control, but tuberculin skin test surveys have major limitations, including poor specificity because of the broad antigenic cross-reactivity of tuberculin. The M. tuberculosis RD1 genomic segment encodes proteins, such as early secretory antigenic target (ESAT)-6, that are absent from M. bovis bacille Calmette-Guérin (BCG) and most environmental mycobacteria. We recently identified circulating ESAT-6-specific T cells as an accurate marker of M. tuberculosis infection. Here, interferon-gamma-secreting T cells specific for peptides derived from ESAT-6 and a second RD1 gene product, CFP10, were enumerated in 100 prospectively recruited healthy adults in Bombay (Mumbai), India. Eighty percent responded to >/=1 antigen, and many donors had high frequencies of T cells that were specific for certain immunodominant peptides. In contrast, of 40 mostly BCG-vaccinated, United Kingdom-resident healthy adults, none responded to either antigen. This study suggests an 80% prevalence of latent M. tuberculosis infection in urban India.

Latency-associated peptide of transforming growth factor beta enhances mycobacteriocidal immunity in the lung during Mycobacterium bovis BCG infection in C57BL/6 mice

Latency-associated peptide of transforming growth factor beta (TGF-beta) (LAP) was used to determine whether in vivo modulation of TGF-beta bioactivity enhanced pulmonary immunity to Mycobacterium bovis BCG infection in C57BL/6 mice. LAP decreased BCG growth in the lung and enhanced antigen-specific T-cell proliferation and gamma interferon mRNA expression. Thus, susceptibility of the lung to primary BCG infection may be partially mediated by the immunosuppressive effects of TGF-beta.

High frequencies of circulating IFN-gamma-secreting CD8 cytotoxic T cells specific for a novel MHC class I-restricted Mycobacterium tuberculosis epitope in M. tuberculosis-infected subjects without disease

MHC class I-restricted CD8 cytotoxic T lymphocytes (CTL) are essential for protective immunity to Mycobacterium tuberculosis in animal models but their role in humans remains unclear. We therefore studied subjects who had successfully contained M. tuberculosis infection in vivo, i.e. exposed healthy household contacts and individuals with inactive self-healed pulmonary tuberculosis. Using the ELISPOT assay for IFN-gamma, we screened peptides from ESAT-6, a secreted antigen that is highly specific for M. tuberculosis. We identified a novel nonamer epitope: unstimulated peripheral blood-derived CD8 T cells displayed peptide-specific IFN-gamma release ex vivo while CD8 T cell lines and clones exhibited HLA-A68.02-restricted cytolytic activity and recognized endogenously processed antigen. The frequency of CD8 CTL specific for this single M. tuberculosis epitope, 1/2500 peripheral blood lymphocytes, was equivalent to the combined frequency of all IFN-gamma-secreting purified protein derivative-reactive T cells ex vivo. This highly focused CTL response was maintained in an asymptomatic contact over 2 years and is the most potent antigen-specific antimycobacterial CD8 CTL response hitherto described. Thus, human M. tuberculosis-specific CD8 CTL are not necessarily associated with active disease per se. Rather, our results are consistent with a protective role for these ESAT-6-specific CD8 T cells in the long-term control of M. tuberculosis in vivo in humans.

Modulation of transforming growth factor beta-1 gene expression by interleukin-12

The interaction of cytokines and their net balance with regard to macrophage activation (or deactivation) and immune stimulation (or suppression), ultimately determines the success of host-immune response at sites of active infection. A regulatory role for interleukin (IL)-12 in production of transforming growth factor (TGF)-beta1 has been suggested, however, remains controversial. In this study, we analyzed the effect of IL-12 on TGF-beta1 expression in the human lines, K562 and A549, and in primary human monocytes and macrophages. We found that IL-12 down-regulates TGF-beta1 mRNA expression in K562, monocytes and bone marrow cells, and to a lesser extent in the A549 cells. Using constructs containing different regions of the first promoter of the TGF-beta1 gene and a reporter gene, we also demonstrate that this effect is mediated through the TGF-beta1 gene promoter in the K562 and monocytic cell types. In conclusion, the critical role of IL-12 in the early activation of the immune response to pathogens may include down-modulation of TGF-beta1 gene activity.

A novel cytokine receptor-ligand pair. Identification, molecular characterization, and in vivo immunomodulatory activity

As part of a large scale effort to discover novel secreted proteins, a cDNA encoding a novel cytokine was identified. Alignments of the sequence of the new protein, designated IL-17B, suggest it to be a homolog of the recently described T cell-derived cytokine, IL-17. By Northern analysis, EST distribution and real-time quantitative polymerase chain reaction analysis, mRNA was detected in many cell types. A novel type I transmembrane protein, identified in an EST data base by homology to IL-17R, was found to bind specifically IL-17B, as determined by surface plasmon resonance analysis, flow cytometry, and co-immunoprecipitation experiments. Readily detectable transcription of IL-17BR was restricted to human kidney, pancreas, liver, brain, and intestines and only a few of the many cell lines tested. By using a rodent ortholog of IL-17BR as a probe, IL-17BR message was found to be drastically up-regulated during intestinal inflammation elicited by indomethacin treatment in rats. In addition, intraperitoneal injection of IL-17B purified from Chinese hamster ovary cells caused marked neutrophil migration in normal mice, in a specific and dose-dependent manner. Together these results suggest that IL-17B may be a novel proinflammatory cytokine acting on a restricted set of target cell types. They also demonstrate the strength of genomic approaches in the unraveling of novel biological pathways.

Enhancement of the human T cell response to culture filtrate fractions of Mycobacterium tuberculosis by microspheres

An improved method of assessment of the human immune response against Mycobacterium tuberculosis antigens will assist the development of new vaccines or diagnostic reagents. In this study, we have analyzed human T cell responses to culture filtrate fractions (CFF) of actively replicating M. tuberculosis strain H37Rv using peripheral blood mononuclear cells from healthy PPD skin test positive and negative individuals. Adsorption of CFF onto polystyrene microspheres, that were approximately the size of the M. tuberculosis (bead-adsorbed antigens, BAA) significantly enhanced IFN-gamma production compared to soluble antigens (SA) in PPD skin test positive individuals in an antigen-specific manner. Further, BAA induced activation of both CD4(+) and CD8(+) T cell subsets. However, CD4(+) responses in general were higher and their antigenic repertoire was wider than the CD8(+) responses. By contrast, CD8(+) responses were strongest to the lower molecular weight BAA. When CFF were chemically coupled to carboxyl modified microspheres (bead-coupled antigens, BCA), induction of IFN-gamma was similar to BAA. Enhancement of T cell responses to particulate M. tuberculosis antigens may prove useful in vaccine design strategies.

Enhancement of the T cell response to a mycobacterial peptide by conjugation to synthetic branched polypeptide

A peptide-based approach towards improving the immunodiagnosis of, and vaccination against, tuberculosis faces the problems of MHC restriction of T cell recognition and the poor immunogenicity of peptides in the absence of adjuvant. We sought to compensate this by the use of synthetic branched polypeptides of the poly[Lys-(Xi-DL-Alam)] type, containing a glutamic acid residue (EAK), and further modified either by succinylation (SucEAK) or acetylation (AcEAK). These carriers were conjugated to two permissively recognized peptides of Mycobacterium tuberculosis. The 38p350 - 369-SucEAK conjugate enhanced IFN-gamma production more than 13-fold (from 22.6 to 294 pg / ml, p = 0.001) in peripheral blood mononuclear cells from healthy subjects, and 8.7-fold (p = 0. 012) in cells from tuberculosis patients. The effect was dependent on the carrier used and on covalent linkage of SucEAK to 38p350 - 369. An increased response occurred best in cells from subjects bearing at least one HLA-DR allele for which 38p350 - 369 had high binding affinity and required cellular processing of the conjugate as inhibitors (chloroquine and wortmannin) blocked the IFN-gamma response. SucEAK conjugation of peptide 16p91 - 110 did not significantly increase IFN-gamma production, indicating that the ability of conjugation to enhance the response was peptide structure dependent. These data indicate that the use of SucEAK polymer coupled with permissively recognized peptides could contribute to the development of an improved immunodiagnostic or vaccine reagent for tuberculosis.

Immune responses to recombinant proteins of Mycobacterium leprae

Identification of antigenic determinants of the polar immune response in leprosy may illuminate both protection and pathogenesis. Thirty subjects were studied (22 with polar disease and 8 healthy controls who were heavily exposed but disease-free) by assaying the proliferative, interferon (IFN)-gamma, and antibody responses to recombinant antigens of Mycobacterium leprae (10, 28, 36, and 65 kDa). The 10-kDa antigen elicited IFN-gamma production from all tuberculoid (TT) and borderline tuberculoid (BT) patients but little from controls, lepromatous (LL), or borderline lepromatous (BL) patients (P<.05). Production of 65-kDa-specific IFN-gamma was higher in TT/BT than in controls or LL/BL patients (P<.006). All subjects produced 65-kDa-specific antibody, but it was higher in LL/BL patients than in healthy controls, whose responses were higher than in TT/BT subjects (P=.035). The 36-kDa antibody responses were selectively increased in LL/BL subjects (P<.02). The intermediate phenotype of the controls suggests that M. leprae-specific production of IFN-gamma may contribute to pathology and to protection in leprosy.

Specificity and function of immunogenic peptides from the 35-kilodalton protein of Mycobacterium leprae

We identified a T-cell determinant of the 35-kDa antigen of Mycobacterium leprae which is discriminatory against cross-sensitization by its closely related homologue in Mycobacterium avium. From synthetic peptides covering the entire sequence, those with the highest affinity and permissive binding to purified HLA-DR molecules were evaluated for the stimulation of proliferation of peripheral blood mononuclear cells (PBMCs) from leprosy patients and healthy sensitized controls. Responses to the peptide pair 206-224, differing by four residues between M. leprae and M. avium, involved both species-specific and cross-reactive T cells. Lymph node cell proliferation in HLA-DRB1*01 transgenic mice was reciprocally species specific, but only the response to the M. leprae peptide in the context of DR1 was immunodominant. Of the cytokines in human PBMC cultures, gamma interferon production was negligible, while interleukin 10 (IL-10) responses in both patients and controls were more pronounced. IL-10 was most frequently induced by the shared 241-255 peptide, indicating that environmental cross-sensitization may skew the response toward a potentially pathogenic cytokine phenotype.

38 000 MW antigen-specific major histocompatibility complex class I restricted interferon-gamma-secreting CD8+ T cells in healthy contacts of tuberculosis

CD8+ T lymphocytes are required to protect mice against Mycobacterium tuberculosis, although in early infection the mechanism appears not to be via perforin or granzyme-mediated lysis of the infected target, and may be via interferon-gamma (IFN-gamma) production. We therefore investigated whether CD8+ T cells specific for the immunoprotective 38 000 MW antigen of M. tuberculosis could be detected in infected humans. Using a recombinant vaccinia virus expressing the 38 000 MW antigen of M. tuberculosis (rV38) and a control vaccinia virus (rVras) we demonstrated that both viruses stimulated IFN-gamma production from freshly isolated peripheral blood mononuclear cells (PBMC) in a 36-hr enzyme-linked immunospot assay. Cell depletion and antibody blockade established that the bulk of the 38 000 MW antigen-specific IFN-gamma response was mediated by CD8+, major histocompatibility complex class I-restricted T cells, whereas the anti-vaccinia virus response was predominantly mediated by CD4+ T cells. In further evaluations PBMC from all seven healthy tuberculosis-exposed contacts had a 38 000 MW antigen-specific IFN-gamma response, whereas seven patients with untreated sputum-positive pulmonary tuberculosis had very low levels of 38 000 antigen-specific IFN-gamma-producing cells. These preliminary observations demonstrate the utility of recombinant vaccinia viruses in restimulating freshly isolated CD4+ and CD8+ T cells. The bias towards a higher frequency of IFN-gamma-producing CD8+ T cells in contacts rather than patients may indicate a protective role for CD8+ cells in human tuberculosis.

Human T- and B-cell reactivity to the 16kDa alpha-crystallin protein of Mycobacterium tuberculosis

The attributes of immunodominance, predominant expression during mycobacterial dormancy and restriction to the Mycobacterium tuberculosis complex make the 16 kDa protein an important candidate for the study of the immune response in humans. We therefore investigated the relationship between T- and B-cell reactivity to the recombinant antigen and disease in a total of 127 subjects. The percentage of T-cell responders towards both the intact antigen and its permissively recognised peptide 16p91-110 was highest in healthy bacillus Calmette-Guérin (BCG)-sensitized controls (96% and 68%, respectively) and lowest in those with extensive untreated tuberculosis (26% and 18%) (P < 0.001). By contrast, antibody levels (ABT50 > 100) were highest in patients with extensive disease (46-50%) (P < 0.005). There was significantly higher production of IFN-gamma in the BCG-sensitized controls by comparison with untreated patients (P < 0.05), but complete antituberculous chemotherapy abolished this deficit in patients. The significance of these findings to immunodiagnosis and protective immunity is discussed.

Synthesis and in vitro T-cell immunogenicity of conjugates with dual specificity: attachment of epitope peptides of 16 and 38 kDa proteins from Mycobacterium tuberculosis to branched polypeptide

T-cell epitope containing peptides covalently attached to macromolecular carriers can be considered as synthetic immunogens for the development of skin-test diagnostics and of vaccines. As a carrier, an amphoteric branched chain polypeptide, poly[Lys-(Glui-DL-Alam)] (EAK) with poly(L-lysine) backbone has been used. This polypeptide with free alpha-amino and gamma-carboxyl groups at the end of the side chains was conjugated with peptides representing two immunodominant regions of the 16 and 38 kDa proteins of Mycobacterium tuberculosis, respectively. Peptide C91SEFAYGSFVRTVSLPVGADE110 was elongated by Cys at the N-terminal and attached to the carrier containing protected SH groups to form disulfide bridges. Peptide 65FNLWGPAFHERYPNVTITA83 was conjugated to the 3-(2-pyridyldithio)propionic acid N-hydroxysuccinimide ester (SPDP) modified and acetylated EAK by introducing amide bond between the free alpha-amino group of peptide and the free gamma-COOH group of Glu at the terminal position of the branches. This strategy lead to chemically well-defined synthetic immunogens that contain two different epitopes in multiple copies covalently linked to a synthetic branched polypeptide carrier. In vitro T-cell immunogenicity of a prototype conjugate was studied using T-cell hybridomas, lymph node cells from 38 kDa protein immunized mice, and human peripheral blood mononuclear cell (PBMC) cultures from sensitized individuals. These data document that the specific T-cell stimulatory effect of each mycobacterial epitope was maintained in this conjugate. Taken together, these findings suggest that it is feasible to use a biodegradable polymeric polypeptide for producing macromolecular bioconjugates for the stimulation of T-cell responses.

Peptide-specific T cell response to Mycobacterium tuberculosis: clinical spectrum, compartmentalization, and effect of chemotherapy

The T cell repertoire of 59 patients with untreated tuberculosis was compared with that of 46 bacille Calmette-Guérin-vaccinated controls by assaying the proliferative responses to six permissively recognized peptides from the 16-, 19-, and 38-kDa molecules of Mycobacterium tuberculosis. A trend from higher to lower reactivity following this order: vaccinated controls > lymph node disease > localized extrapulmonary > pulmonary > pleural was seen for 4 of the peptides (P < .03). The decreased response of blood lymphocytes from patients with pleural tuberculosis was partially accounted for by sequestration of peptide-responsive cells within the pleural fluid. Chemotherapy "reversed" the depressed proliferative responses of patients with pulmonary and pleural tuberculosis depending on the peptide origin, being greatest for peptides of 16 kDa, transient for those of 19 kDa, and least for those of 38 kDa. These data demonstrate antigen specificity in the decreased responsiveness of patients with tuberculosis.

Modulation of peptide specific T cell responses by non-native flanking regions

The deduced core (75RYPNVTI81) from a T-cell stimulatory epitope of the 38 kDa protein of M. tuberculosis was studied to identify the structural elements required for the creation of a synthetic peptide antigen from an epitope core, which alone was not capable of inducing CD4+ T-cell responses. Peptides were prepared with extensions composed of native and/or non-native sequences to clarify the role of the flanking regions adjacent to the epitope core. Their binding to isolated H-2-Ab MHC glycoprotein as well as T-cell stimulatory capacity were assayed using a specific murine hybridoma T-cell line [38.H6], lymph node cells from the native 20-mer peptide primed C57BL/10 mice and human PBMCs from sensitised individuals. Elongation of the epitope core by four alanines at both N- and C-terminals resulted in a 15-mer peptide A4-75-81-A4 which was stimulatory for hybridoma T-cells and showed a small decrease in H-2-Ab binding. Substitution of one Ala by Ser in the N-terminal flank had pronounced effect and peptide A2SA-75-81-A4 proved to be more effective than the native 20-mer sequence in the hybridoma as well as in the LN cell proliferation assays. The binding of this peptide and that of the native one were similar. Testing in human PBMC cultures from eight PPD positive individuals showed that in 50% of the donors' cells responded to the 'artificial' A2SA-75-81-A4 peptide. These results suggest that it is possible to construct simple, synthetic CD4+ T-cell stimulatory peptides of high potency from a non-stimulatory, 'silent' epitope core by addition of flanking residues not part of the native sequence.

Unexpected brainstem compression following routine surgery in a child with oto-palato-digital syndrome

Oto-palato-digital syndrome type 1 is a rare condition with several features of concern to the anaesthetist. We report a patient who developed respiratory depression 5 h after general anaesthesia. This was subsequently found to be due to brainstem compression secondary to congenital deformities of the skull base and cervical vertebrae.

Gastric emptying in patients the day after cardiac surgery

Fourteen adults underwent cardiac surgery with a standard anaesthetic technique. Prior to surgery and the day after surgery, gastric emptying was determined using the paracetamol absorption technique. Results from 13 patients were available for analysis. The mean time to reach the maximum plasma concentration was 14.1 min (SEM 2.1) pre-operatively and 225.4 min (SEM 42.3) postoperatively. The mean maximum concentration was 23.7 mg.l-1 (SEM 1.9) pre-operatively and 5.1 mg.l-1 (SEM 0.8) postoperatively. The area under the curve (0-60 min) was 892 mg min.l-1 (SEM 57) pre-operatively and 131 mg min.l-1 (SEM 25) postoperatively. The differences between pre- and postoperative values were highly significant for all these three measurements. We conclude that gastric emptying is markedly delayed the day after elective cardiac surgery.

Surfactant adjunctive therapy for Pneumocystis carinii pneumonitis in an infant with acute lymphoblastic leukaemia

We report successful treatment of adult respiratory distress syndrome (ARDS) with artificial surfactant (40mg/kg, Colfosceril Palmitate, ‘Exosurf’, Wellcome) in an infant with severePneumocystis carinii pneumonitis.

Determination of paracetamol (acetaminophen) in blood and plasma using high performance liquid chromatography with dual electrode coulometric quantification in the redox mode

A simple, but sensitive, micro-assay for paracetamol in blood and plasma is described. Samples were prepared by precipitation with trichloroacetic assay solution and the drug quantified by reversed phase liquid chromatography with dual electrode electrochemical detection in the redox mode (oxidation at +0.25 V followed by reduction at -0.15 V). The limit of detection was 0.1 mg/L for a 10 microL sample of blood or plasma, the coefficient of variation at this concentration being 11.4%. The method was applied to a study of gastric emptying in patients before and after cardiac surgery.

Pneumothorax secondary to foreign body inhalation in a 20 month old child

A 20 month old child presented with acute onset of respiratory embarrassment as a result of a left-sided tension pneumothorax. This proved to be caused by inhalation of an unusual foreign body: the hair from a rag doll.

Assessment of a hygroscopic heat and moisture exchanger for paediatric use

A laboratory study of a widely available heat and moisture exchanger marketed for paediatric use was undertaken. The deadspace, measured by volume displacement, was 12 ml, similar to that of a standard catheter mount for paediatric use. Pressure drop across the device was measured at several different flows in five samples of the device in both the dry and wet state. Calculated resistance proved to be markedly lower when compared with that of other anaesthetic equipment such as tracheal tubes, and with similar humidification devices for paediatric use.