Divergent Functions of TLR2 on Hematopoietic and Nonhematopoietic Cells during Chronic Mycobacterium tuberculosis Infection

We have reported that TLR2 is crucial for host resistance against chronic Mycobacterium tuberculosis infection; however, which cell types are key players in this response remain unknown. This led us to decipher the relative contribution of TLR2 on nonhematopoietic and hematopoietic cells in resistance against chronic M. tuberculosis infection in mice infected with M. tuberculosis Erdman. Consistent with our previous report, at 8 wk of infection, TLR2 knockout (TLR2KO)→TLR2KO bone marrow chimeric mice exhibited increased bacterial burden, disorganized accumulation of lymphocytes and mononuclear cells, and extensive pulmonary immunopathology compared with wild-type (WT)→WT chimeric mice. Bacterial burden and pulmonary immunopathology of chimeric mice lacking TLR2 in the hematopoietic compartment (TLR2KO→WT) was comparable to TLR2KO mice. In contrast, chimeric mice deficient in TLR2 in the nonhematopoietic compartment (WT→TLR2KO) exhibited a marked attenuation in granulomatous inflammation compared with WT mice. Although the latter mice did not exhibit improved pulmonary bacterial control, significant reductions in bacterial burden in the draining lymph nodes, spleen, and liver were observed. These findings establish that the TLR2-mediated hematopoietic response promotes stable control of pulmonary bacterial burden and granuloma integrity, whereas TLR2 signaling on nonhematopoietic cells may partly facilitate granulomatous inflammation and bacterial dissemination.

A foil to itself: TLR2 signaling protects and damages host tissue during Mycobacterium tuberculosis infection (MPF1P.773)

TLR2 polymorphisms have been associated with increased susceptibility to tuberculosis (TB). We have demonstrated that TLR2 is critical for host resistance against Mtb infection and limits immunopathology in the lung. Recent publications illustrating a role for epithelial cells in host immunity against Mtb led us to investigate TLR2’s role in hematopoietic (H) cells and nonhematopoietic (NH) cells in host defense against Mtb. We generated radiation bone marrow chimeric mice, which lack TLR2 either in the H, NH, or both compartments, and infected these mice with Erdman Mtb. Our results show that TLR2 signaling on the H component is crucial for control of chronic murine Mtb infection. Loss of TLR2 in the H component resulted in increased bacterial burden, decreased accumulation of regulatory T cells, and disruption of granuloma architecture. In contrast, loss of TLR2 on the NH compartment resulted in decreased inflammation and dissemination of Mtb to extrapulmonary sites. These data illustrate a novel role for TLR2 and a paradox within TLR2 signaling: TLR2 signaling on H cells is protective to the host both by controlling infection and regulating inflammation while on NH cells it promotes inflammation induced immunopathology. This balanced response is essential to maintaining host control of TB and could lead to the development of cell-specific TLR2 inhibitors.

Co-infection with Nippostrongylus brasiliensis does not impair host resistance during chronic Mycobacterium tuberculosis infection: a protective role for granulomas? (P3094)

Helminths are known to exert immunomodulatory effects on the host, an effect largely mediated by their induction of generalized Th2 responses. In a recent study, using the murine nematode Nippostrongylus brasiliensis (Nb), we have shown that a prior infection with Nb makes the host more susceptible to tuberculosis (TB). In this study we sought to investigate whether coinfection would exacerbate chronic infection, a phase where Mycobacterium tuberculosis (Mtb) is contained within granulomas. Mice chronically infected with Mtb were coinfected with Nb. We report herein that despite a helminth induced Th2 component, coinfected animals had a similar bacterial burden in comparison with Mtb alone infected animals. This observation could be due to the fact that the Mtb is already established in the granuloma and any effect of the helminth induced Th2 response is unable to shift this balance. In order to further understand the kinetics of helminths influencing TB, we infected mice with Mtb and these were infected 5days later with Nb. Interestingly we observed a significant increase in lung bacterial burden in coinfected animals. These results suggest that the timing of a helminth infection in an Mtb infected individual could have completely different outcomes. Studies are underway to unravel the mechanisms behind these observations. This finding is significant as a helminth infection can occur even during adulthood in endemic areas of the world, regions which are also endemic with TB

Sustained generation of nitric oxide and control of mycobacterial infection requires argininosuccinate synthase 1

Nitric oxide (NO) defends against intracellular pathogens, but its synthesis must be regulated due to cell and tissue toxicity. During infection, macrophages import extracellular arginine to synthesize NO, generating the byproduct citrulline. Accumulated intracellular citrulline is thought to fuel arginine synthesis catalyzed by argininosuccinate synthase (Ass1) and argininosuccinate lyase (Asl), which would lead to abundant NO production. Instead, we find that citrulline is exported from macrophages during early stages of NO production with <2% retained for recycling via the Ass1-Asl pathway. Later, extracellular arginine is depleted, and Ass1 expression allows macrophages to synthesize arginine from imported citrulline to sustain NO output. Ass1-deficient macrophages fail to salvage citrulline in arginine-scarce conditions, leading to their inability to control mycobacteria infection. Thus, extracellular arginine fuels rapid NO production in activated macrophages, and citrulline recycling via Ass1 and Asl is a fail-safe system that sustains optimum NO production.

Imatinib-sensitive tyrosine kinases regulate mycobacterial pathogenesis and represent therapeutic targets against tuberculosis

The lengthy course of treatment with currently used antimycobacterial drugs and the resulting emergence of drug-resistant strains have intensified the need for alternative therapies against Mycobacterium tuberculosis (Mtb), the etiologic agent of tuberculosis. We show that Mtb and Mycobacterium marinum use ABL and related tyrosine kinases for entry and intracellular survival in macrophages. In mice, the ABL family tyrosine kinase inhibitor, imatinib (Gleevec), when administered prophylactically or therapeutically, reduced both the number of granulomatous lesions and bacterial load in infected organs and was also effective against a rifampicin-resistant strain. Further, when coadministered with current first-line drugs, rifampicin or rifabutin, imatinib acted synergistically. These data implicate host tyrosine kinases in entry and intracellular survival of mycobacteria and suggest that imatinib may have therapeutic efficacy against Mtb. Because imatinib targets host, it is less likely to engender resistance compared to conventional antibiotics and may decrease the development of resistance against coadministered drugs.

Preexisting helminth infection induces inhibition of innate pulmonary anti-tuberculosis defense by engaging the IL-4 receptor pathway

Preexisting helminth infection impairs immunity against subsequent M. tuberculosis infection, in part by inducing alternatively activated macrophages.

Tuberculosis and helminthic infections coexist in many parts of the world, yet the impact of helminth-elicited Th2 responses on the ability of the host to control Mycobacterium tuberculosis (Mtb) infection has not been fully explored. We show that mice infected with the intestinal helminth Nippostrongylus brasiliensis (Nb) exhibit a transitory impairment of resistance to airborne Mtb infection. Furthermore, a second dose of Nb infection substantially increases the bacterial burden in the lungs of co-infected mice. Interestingly, the Th2 response in the co-infected animals did not impair the onset and development of the protective Mtb-specific Th1 cellular immune responses. However, the helminth-induced Th2 environment resulted in the accumulation of alternatively activated macrophages (AAMs) in the lung. Co-infected mice lacking interleukin (IL) 4Rα exhibited improved ability to control Mtb infection, which was accompanied by significantly reduced accumulation of AAMs. Moreover, IL-4Rα^−/− mice adoptively transferred with wild-type macrophages had a significantly higher Mtb load in their lungs compared with those that received IL-4Rα^−/− macrophages, suggesting a direct contribution for the IL-4R pathway to the heightened susceptibility of co-infected animals. The Th2 response can thus enhance the intracellular persistence of Mtb, in part by mediating the alternative activation of macrophages via the IL-4Rα signaling pathway.

B7.1 and B7.2 are crucial for primary response to Mycobacterium tuberculosis infection but redundant for the induction of memory response (45.24)

Costimulation plays a crucial role in priming of naïve T cell to an effector cell type. In a recent study, we have shown that lack of B7.1 and B7.2 (DKO) causes the host to generate a dampened Th1 effector response, disabling it to contain the bacterial burden during chronic phase of infection. Since the development of T cell memory is connected to the effector T cell response, we sought to investigate how a defective primary effector response will affect the induction of the memory. Memory mice were generated by treating infected wildtype (WT) and DKO mice with antibiotics and resting them after the treatment. These memory mice along with age matched naïve controls were then challenged with low dose infection with M. tuberculosis. A significant decrease in bacterial burden was seen in both WT and DKO memory mice at 4 and 6 weeks post infection when compared to naive WT and DKO mice respectively. This decreased bacterial burden was accompanied with a faster Th1 effector response in both WT and DKO memory lungs as indicated by increased number of IFNγ producing cells in the lungs. These results indicate that despite its inability to generate a defective primary response the DKO host is able to mount a memory response against M.tuberculosis infection. Further studies are in progress to study the mechanism of memory induction in the absence of a successful primary response in the DKO mice.

This study was supported by NIH Grant AI 49778, Potts Memorial Foundation Award and UMDNJ Foundation Award.

Drug susceptibility profiling of tuberculous meningitis

Drug-resistant tuberculosis is an increasing problem worldwide. There are few reports of drug susceptibility patterns of Mycobacterium tuberculosis isolated from cases of tuberculous meningitis. A 5-year retrospective study aimed at analysing the drug susceptibility profile of M. tuberculosis isolated from tuberculous meningitis cases was conducted. A total of 366 isolates were analysed. Among these, 301 (82.2%) were sensitive to all the four primary drugs tested, while 65 (17.8%) showed resistance. There were 46 (12.5%) isolates resistant to isoniazid (INH), while 9 (2.4%) demonstrated multidrug resistance. These data suggest that multidrug resistance in tuberculous meningitis is not yet a serious problem. However, a periodic review is required to ascertain the global incidence of drug-resistant tuberculous meningitis.

Role of IS6110 uniplex PCR in the diagnosis of tuberculous meningitis: experience at a tertiary neurocentre

SETTING

Tuberculous meningitis (TBM) is the commonest form of neurotuberculosis in the Indian subcontinent. Rapid laboratory confirmation of TBM is important for the institution of early treatment and to avoid associated morbidity and mortality. The polymerase chain reaction (PCR) is the most widely applied alternative rapid diagnostic technique for TBM.

OBJECTIVE

To evaluate the efficacy of an in-house developed IS6110 uniplex PCR (uPCR) in the diagnosis of TBM.

DESIGN

A prospective, blinded study was conducted in a large sample base of 677 cerebrospinal fluid samples from 677 patients with clinically suspected TBM.

RESULTS

All culture-positive samples (n = 136) were positive (100%) by the PCR assay. The assay was found to be positive in 70% (n = 541) of the samples with a clinical diagnosis of TBM. The assay had an observed sensitivity of 76.37% (negative predictive value 59.90%) and a specificity of 89.18% (positive predictive value 94.69%). A diagnostic accuracy of 80% (kappa 0.57) was seen in patients with a clinical diagnosis of TBM. Statistical significance was observed, as patients with a clinical diagnosis of TBM were found to be 9.38 times more likely to be PCR-positive (OR 9.38, chi2 = 149.94, P < 0.001).

CONCLUSION

The performance of the in-house IS6110 uPCR assay merits its use as a sensitive and specific tool for the rapid diagnosis of TBM.

Comparative evaluation of bactec 460tb system and lowenstein-jensen medium for the isolation of <i>M. tuberculosis</i> from cerebrospinal fluid samples of tuberculous meningitis patients

PURPOSE

To evaluate the role of the radiometric BACTEC 460TB system and the conventional Lowenstein-Jensen (LJ) medium for isolation of M. tuberculosis from cerebrospinal fluid (CSF) samples of tuberculous meningitis (TBM) patients.

METHODS

CSF specimens (n=2325) from suspected TBM patients were processed for isolation of mycobacteria by inoculating BACTEC 12B medium and the LJ medium. The isolation of mycobacteria in both media was confirmed by microscopy and biochemical identification. Drug sensitivity testing for the anti-TB drugs was carried out by BACTEC radiometric method.

RESULTS

Among the total 2325 CSF specimens processed by both methods, M. tuberculosis was isolated from 256 specimens. The isolation rates were 93% and 39% for the BACTEC system and LJ medium respectively. Both the media supported growth in 32% of the culture-positive specimens. BACTEC system alone yielded growth in 61% and LJ alone in 7%, of the culture-positive specimens. Among 205 isolates tested for drug susceptibility 81% were sensitive to all the drugs tested and 19% were resistant.

CONCLUSIONS

The BACTEC 460TB system provides a highly sensitive and rapid tool for the isolation and drug susceptibility testing of M. tuberculosis, from CSF of TBM patients. Use of a solid medium in conjunction with the BACTEC 12B medium is essential for optimal recovery for M. tuberculosis from CSF specimens.

Rapid diagnosis of tuberculous meningitis: a comparative evaluation of in-house PCR assays involving three mycobacterial DNA sequences, IS6110, MPB-64 and 65 kDa antigen

A PCR was standardized for amplifying three different mycobacterial--IS6110, MPB-64, 65 kDa DNA sequences. A comparative evaluation of the three PCR assays was carried out for the rapid diagnosis of tuberculous meningitis (TBM) using cerebrospinal fluid (CSF) specimens. While the IS6110 PCR was a single-step amplification reaction, the MPB-64 and 65 kDa antigen PCR assays were nested reactions. A total of 176 cerebrospinal fluid (CSF) samples from 176 patients were subjected to amplification of the three different mycobacterial sequences. Amongst them, 45 samples were obtained from confirmed cases of TBM (culture positive) and 56 samples were obtained from clinically suspected cases of TBM which were culture-negative. The remaining 75 CSF samples were categorized under the non-infectious and infectious illness of the central nervous system (CNS). Against a gold standard of culture, a sensitivity of 98% (NPV=99%) and a specificity of 100% (PPV=100%) was observed with the IS6110 PCR. Among the nested PCRs, a sensitivity of 91% (NPV=94%) and a specificity of 91% (PPV=85%) was observed with the MPB-64 assay, while the 65 kDa protocol had an associated sensitivity of 51% (NPV=76%) and a specificity of 92% (PPV=79%). These findings suggest that among the nested PCR assays, the MPB-64 PCR assay was associated with an enhanced degree of sensitivity and was comparable in terms of specificity. Our study also demonstrates that the IS6110 assay, while being a single-step PCR had the advantage of being a rapid test for the diagnosis of TBM, with increased sensitivity and enhanced specificity as compared to the nested PCR protocols.