Inflammatory response following intranasal infection with Mycobacterium avium complex: role of T-cell subsets and gamma interferon

Additive Effects of Cyclic Peptide [R4W4] When Added Alongside Azithromycin and Rifampicin against Mycobacterium avium Infection

Mycobacterium avium (M. avium), a type of nontuberculous mycobacteria (NTM), poses a risk for pulmonary infections and disseminated infections in immunocompromised individuals. Conventional treatment consists of a 12-month regimen of the first-line antibiotics rifampicin and azithromycin. However, the treatment duration and low antibiotic tolerability present challenges in the treatment of M. avium infection. Furthermore, the emergence of multidrug-resistant mycobacterium strains prompts a need for novel treatments against M. avium infection. This study aims to test the efficacy of a novel antimicrobial peptide, cyclic [R4W4], alongside the first-line antibiotics azithromycin and rifampicin in reducing M. avium survival. Colony-forming unit (CFU) counts were assessed after treating M. avium cultures with varying concentrations of cyclic [R4W4] alone or in conjunction with azithromycin or rifampicin 3 h and 4 days post-treatment. M. avium growth was significantly reduced 4 days after cyclic [R4W4] single treatment. Additionally, cyclic [R4W4]-azithromycin and cyclic [R4W4]-rifampicin combination treatments at specific concentrations significantly reduced M. avium survival 3 h and 4 days post-treatment compared with single antibiotic treatment alone. These findings demonstrate cyclic [R4W4] as a potent treatment method against M. avium and provide insight into novel therapeutic approaches against mycobacterium infections.

Depletion of PD-1 or PD-L1 did not affect the mortality of mice infected with Mycobacterium avium

The programmed cell death-1 (PD-1) and programmed cell death-ligand 1 (PD-L1) pathway could affect antimicrobial immune responses by suppressing T cell activity. Several recent studies demonstrated that blocking of the PD-1/PD-L1 pathway exacerbated Mycobacterium tuberculosis infection. However, the effect of blocking this pathway in pulmonary Mycobacterium avium–intracellulare complex (MAC) infection is not fully understood. Wild-type, PD-1-deficient mice, and PD-L1-deficient mice were intranasally infected with Mycobacterium avium bacteria. Depletion of PD-1 or PD-L1 did not affect mortality and bacterial burden in MAC-infected mice. However, marked infiltration of CD8-positive T lymphocytes was observed in the lungs of PD-1 and PD-L1-deficient mice compared to wild-type mice. Comprehensive transcriptome analysis showed that levels of gene expressions related to Th1 immunity did not differ according to the genotypes. However, genes related to the activity of CD8-positive T cells and related chemokine activity were upregulated in the infected lungs of PD-1 and PD-L1-deficient mice. Thus, the lack of change in susceptibility to MAC infection in PD-1 and PD-L1-deficient mice might be explained by the absence of obvious changes in the Th1 immune response. Furthermore, activated CD8-positive cells in response to MAC infection in these mice seemed to not be relevant in the control of MAC infection.

General Overview of Nontuberculous Mycobacteria Opportunistic Pathogens: Mycobacterium avium and Mycobacterium abscessus

Nontuberculous mycobacteria (NTM) are emerging human pathogens, causing a wide range of clinical diseases affecting individuals who are immunocompromised and who have underlying health conditions. NTM are ubiquitous in the environment, with certain species causing opportunistic infection in humans, including Mycobacterium avium and Mycobacterium abscessus. The incidence and prevalence of NTM infections are rising globally, especially in developed countries with declining incidence rates of M. tuberculosis infection. Mycobacterium avium, a slow-growing mycobacterium, is associated with Mycobacterium avium complex (MAC) infections that can cause chronic pulmonary disease, disseminated disease, as well as lymphadenitis. M. abscessus infections are considered one of the most antibiotic-resistant mycobacteria and are associated with pulmonary disease, especially cystic fibrosis, as well as contaminated traumatic skin wounds, postsurgical soft tissue infections, and healthcare-associated infections (HAI). Clinical manifestations of diseases depend on the interaction of the host's immune response and the specific mycobacterial species. This review will give a general overview of the general characteristics, vulnerable populations most at risk, pathogenesis, treatment, and prevention for infections caused by Mycobacterium avium, in the context of MAC, and M. abscessus.

Mycobacterium smegmatis Vaccine Vector Elicits CD4+ Th17 and CD8+ Tc17 T Cells With Therapeutic Potential to Infections With Mycobacterium avium

Mycobacterium avium (Mav) complex is increasingly reported to cause non-tuberculous infections in individuals with a compromised immune system. Treatment is complicated and no vaccines are available. Previous studies have shown some potential of using genetically modified Mycobacterium smegmatis (Msm) as a vaccine vector to tuberculosis since it is non-pathogenic and thus would be tolerated by immunocompromised individuals. In this study, we used a mutant strain of Msm disrupted in EspG₃, a component of the ESX-3 secretion system. Infection of macrophages and dendritic cells with Msm ΔespG₃ showed increased antigen presentation compared to cells infected with wild-type Msm. Vaccination of mice with Msm ΔespG₃, expressing the Mav antigen MPT64, provided equal protection against Mav infection as the tuberculosis vaccine, Mycobacterium bovis BCG. However, upon challenge with Mav, we observed a high frequency of IL-17-producing CD4+ (Th17 cells) and CD8+ (Tc17 cells) T cells in mice vaccinated with Msm ΔespG₃::mpt64 that was not seen in BCG-vaccinated mice. Adoptive transfer of cells from Msm ΔespG₃-vaccinated mice showed that cells from the T cell compartment contributed to protection from Mav infection. Further experiments revealed Tc17-enriched T cells did not provide prophylactic protection against subsequent Mav infection, but a therapeutic effect was observed when Tc17-enriched cells were transferred to mice already infected with Mav. These initial findings are important, as they suggest a previously unknown role of Tc17 cells in mycobacterial infections. Taken together, Msm ΔespG₃ shows promise as a vaccine vector against Mav and possibly other (myco)bacterial infections.

Global Assessment of Mycobacterium avium subsp. hominissuis Genetic Requirement for Growth and Virulence

Nontuberculous mycobacterial infections caused by the opportunistic pathogen Mycobacterium avium subsp. hominissuis (MAH) are currently receiving renewed attention due to increased incidence combined with difficult treatment. Insights into the disease-causing mechanisms of this species have been hampered by difficulties in genetic manipulation of the bacteria. Here, we identified and sequenced a highly transformable, virulent MAH clinical isolate susceptible to high-density transposon mutagenesis, facilitating global gene disruption and subsequent investigation of MAH gene function. By transposon insertion sequencing (TnSeq) of this strain, we defined the MAH genome-wide genetic requirement for virulence and in vitro growth and organized ∼3,500 identified transposon mutants for hypothesis-driven research. The majority (96%) of the genes we identified as essential for MAH in vitro had a mutual ortholog in the related and highly virulent Mycobacterium tuberculosis (Mtb). However, passaging our library through a mouse model of infection revealed a substantial number (54% of total hits) of novel virulence genes. More than 97% of the MAH virulence genes had a mutual ortholog in Mtb Finally, we validated novel genes required for successful MAH infection: one encoding a probable major facilitator superfamily (MFS) transporter and another encoding a hypothetical protein located in the immediate vicinity of six other identified virulence genes. In summary, we provide new, fundamental insights into the underlying genetic requirement of MAH for growth and host infection.IMPORTANCE Pulmonary disease caused by nontuberculous mycobacteria is increasing worldwide. The majority of these infections are caused by the Mycobacterium avium complex (MAC), whereof >90% are due to Mycobacterium avium subsp. hominissuis (MAH). Treatment of MAH infections is currently difficult, with a combination of antibiotics given for at least 12 months. To control MAH by improved therapy, prevention, and diagnostics, we need to understand the underlying mechanisms of infection. Here, we provide crucial insights into MAH's global genetic requirements for growth and infection. We find that the vast majority of genes required for MAH growth and virulence (96% and 97%, respectively) have mutual orthologs in the tuberculosis-causing pathogen M. tuberculosis (Mtb). However, we also find growth and virulence genes specific to MAC species. Finally, we validate novel mycobacterial virulence factors that might serve as future drug targets for MAH-specific treatment or translate to broader treatment of related mycobacterial diseases.

BCG Vaccination Induces M. avium and M. abscessus Cross-Protective Immunity

Pulmonary non-tuberculous mycobacterial (NTM) infections particularly caused by Mycobacterium avium complex (MAC) and Mycobacterium abscessus (MAB) are becoming major health problems in the U.S. New therapies or vaccines which will help prevent the disease, shorten treatment duration and/or increase treatment success rates are urgently needed. This study was conducted with the objective of testing the hypothesis that Bacillus Calmette Guerin (BCG), a vaccine used for prevention of serious forms of tuberculosis (TB) in children and adolescents in tuberculosis hyperendemic countries, induces cross-protective T cell immunity against Mycobacterium avium (MAV) and MAB. Human TB and NTM cross-protective T cells were quantified using flow cytometric assays. The ability of BCG expanded T cells to inhibit the intracellular growth of MAV and MAB was assessed in co-cultures with infected autologous macrophages. In both BCG-vaccinated and M. tuberculosis (Mtb)-infected mice, NTM cross-reactive immunity was measured using IFN-γ ELISPOT assays. Our results demonstrate the following key findings: (i) peripheral blood mononuclear cells from TB skin test-positive individuals contain MAV and MAB cross-reactive T cells, (ii) both BCG vaccination and Mtb infection of mice induce MAV and MAB cross-reactive splenic cells, (iii) BCG-expanded T cells inhibit intracellular MAV and MAB, (iv) CD4, CD8, and γδ T cells play important roles in inhibition of intracellular MAV and MAB and (v) BCG vaccination of healthy volunteers induces TB and NTM cross-reactive T cells. In conclusion, BCG-vaccination induces NTM cross-reactive immunity, and has the potential for use as a vaccine or immunotherapy to prevent and/or treat pulmonary NTM disease.

The complexities and challenges of preventing and treating nontuberculous mycobacterial diseases

Seemingly innocuous nontuberculous mycobacteria (NTM) species, classified by their slow or rapid growth rates, can cause a wide range of illnesses, from skin ulceration to severe pulmonary and disseminated disease. Despite their worldwide prevalence and significant disease burden, NTM do not garner the same financial or research focus as Mycobacterium tuberculosis. In this review, we outline the most abundant of over 170 NTM species and inadequacies of diagnostics and treatments and weigh the advantages and disadvantages of currently available in vivo animal models of NTM. In order to effectively combat this group of mycobacteria, more research focused on appropriate animal models of infection, screening of chemotherapeutic compounds, and development of anti-NTM vaccines and diagnostics is urgently needed.

Lack of the Transcription Factor Hypoxia-Inducible Factor 1α (HIF-1α) in Macrophages Accelerates the Necrosis of Mycobacterium avium-Induced Granulomas

The establishment of mycobacterial infection is characterized by the formation of granulomas, which are well-organized aggregates of immune cells, namely, infected macrophages. The granuloma's main function is to constrain and prevent dissemination of the mycobacteria while focusing the immune response to a limited area. In some cases these lesions can grow progressively into large granulomas which can undergo central necrosis, thereby leading to their caseation. Macrophages are the most abundant cells present in the granuloma and are known to adapt under hypoxic conditions in order to avoid cell death. Our laboratory has developed a granuloma necrosis model that mimics the human pathology of Mycobacterium tuberculosis, using C57BL/6 mice infected intravenously with a low dose of a highly virulent strain of Mycobacterium avium. In this work, a mouse strain deleted of the hypoxia inducible factor 1α (HIF-1α) under the Cre-lox system regulated by the lysozyme M gene promoter was used to determine the relevance of HIF-1α in the caseation of granulomas. The genetic ablation of HIF-1α in the myeloid lineage causes the earlier emergence of granuloma necrosis and clearly induces an impairment of the resistance against M. avium infection coincident with the emergence of necrosis. The data provide evidence that granulomas become hypoxic before undergoing necrosis through the analysis of vascularization and quantification of HIF-1α in a necrotizing mouse model. Our results show that interfering with macrophage adaptation to hypoxia, such as through HIF-1α inactivation, accelerates granuloma necrosis.

Protective efficacy of piperine against Mycobacterium tuberculosis

Piperine a trans-trans isomer of 1-piperoyl-piperidine was evaluated for its immunomodulatory activity to enhance the efficacy of rifampicin in a murine model of Mycobacterium tuberculosis infection. In-vitro immunomodulation of piperine was tested on mouse splenocytes for lymphocyte proliferation, cytokine production and macrophage activation. Protective efficacy of piperine was tested in a mice infection model of M. tuberculosis for the activation of Th-1 response and synergistic combination efficacy with rifampicin. Murine splenocytes exposed to piperine exhibited proliferation of T and B cell, increased Th-1 cytokines and enhanced macrophage activation. Piperine (1 mg/kg) in mice infected with M. tuberculosis activated the differentiation of T cells into Th-1 sub-population (CD4+ / CD8+ subsets). There was an increase in secretion of Th-1 cytokines (IFN-γ and IL-2) by these cells. The qRT-PCR studies revealed corresponding increases in the mRNA transcripts of IFN-γ and IL-2 in the infected lung tissues. Combination of piperine and rifampicin (1 mg/kg) exhibited better efficacy of and resulted in additional 1.4 to 0.8 log reduction in lung cfu as compared to rifampicin alone. The up-regulation of Th1 immunity by piperine can be synergistically combined with rifampicin to improve its therapeutic efficacy in immune-compromised TB patients.

Virulence and immune response induced by Mycobacterium avium complex strains in a model of progressive pulmonary tuberculosis and subcutaneous infection in BALB/c mice

The genus Mycobacterium comprises more than 150 species, including important pathogens for humans which cause major public health problems. The vast majority of efforts to understand the genus have been addressed in studies with Mycobacterium tuberculosis. The biological differentiation between M. tuberculosis and nontuberculous mycobacteria (NTM) is important because there are distinctions in the sources of infection, treatments, and the course of disease. Likewise, the importance of studying NTM is not only due to its clinical significance but also due to the mechanisms by which some species are pathogenic while others are not. Mycobacterium avium complex (MAC) is the most important group of NTM opportunistic pathogens, since it is the second largest medical complex in the genus after the M. tuberculosis complex. Here, we evaluated the virulence and immune response of M. avium subsp. avium and Mycobacterium colombiense, using experimental models of progressive pulmonary tuberculosis and subcutaneous infection in BALB/c mice. Mice infected intratracheally with a high dose of MAC strains showed high expression of tumor necrosis factor alpha (TNF-α) and inducible nitric oxide synthase with rapid bacillus elimination and numerous granulomas, but without lung consolidation during late infection in coexistence with high expression of anti-inflammatory cytokines. In contrast, subcutaneous infection showed high production of the proinflammatory cytokines TNF-α and gamma interferon with relatively low production of anti-inflammatory cytokines such as interleukin-10 (IL-10) or IL-4, which efficiently eliminate the bacilli but maintain extensive inflammation and fibrosis. Thus, MAC infection evokes different immune and inflammatory responses depending on the MAC species and affected tissue.

Comparing adjuvanted H28 and modified vaccinia virus ankara expressingH28 in a mouse and a non-human primate tuberculosis model

Here we report for the first time on the immunogenicity and protective efficacy of a vaccine strategy involving the adjuvanted fusion protein “H28” (consisting of Ag85B-TB10.4-Rv2660c) and Modified Vaccinia Virus Ankara expressing H28. We show that a heterologous prime-boost regimen involving priming with H28 in a Th1 adjuvant followed by boosting with H28 expressed by MVA (H28/MVA28) induced the highest percentage of IFN-γ expressing T cells, the highest production of IFN-γ per single cell and the highest induction of CD8 T cells compared to either of the vaccines given alone. In contrast, in mice vaccinated with adjuvanted recombinant H28 alone (H28/H28) we observed the highest production of IL-2 per single cell and the highest frequency of antigen specific TNF-α/IL-2 expressing CD4 T cells pre and post infection. Interestingly, TNF-α/IL-2 expressing central memory-like CD4 T cells showed a significant positive correlation with protection at week 6 post infection, whereas the opposite was observed for post infection CD4 T cells producing only IFN-γ. Moreover, as a BCG booster vaccine in a clinically relevant non-human primate TB model, the H28/H28 vaccine strategy induced a slightly more prominent reduction of clinical disease and pathology for up to one year post infection compared to H28/MVA28. Taken together, our data showed that the adjuvanted subunit and MVA strategies led to different T cell subset combinations pre and post infection and that TNF-α/IL-2 double producing but not IFN-γ single producing CD4 T cell subsets correlated with protection in the mouse TB model. Moreover, our data demonstrated that the H28 vaccine antigen was able to induce strong protection in both a mouse and a non-human primate TB model.

T cells from lungs and livers of Francisella tularensis-immune mice control the growth of intracellular bacteria

Parenteral and respiratory vaccinations with the intracellular bacterium Francisella tularensis have been studied using the live vaccine strain (LVS) in a mouse model, and spleen cells from immune mice are often used for immunological studies. However, mechanisms of host immunological responses may be different in nonlymphoid organs that are important sites of infection, such as lung and liver. Using parenteral (intradermal) or respiratory (cloud aerosol) vaccination, here we examine the functions of resulting LVS-immune liver or lung cells, respectively. Surprisingly, LVS was considerably more virulent when administered by cloud aerosol than by intranasal instillation, suggesting method-dependent differences in initial localization and/or dissemination patterns. Only low doses were sublethal, and resolution of sublethal cloud aerosol infection was dependent on gamma interferon (IFN-gamma), tumor necrosis factor alpha, and inducible nitric oxide synthase. Nonetheless, survival of cloud aerosol or parenteral infection resulted in the development of a protective immune response against lethal LVS intraperitoneal or aerosol challenge, reflecting development of systemic secondary immunity in both cases. Such immunity was further detected by directly examining the functions of LVS-immune lung or liver lymphocytes in vitro. Lung lymphocytes primed by respiratory infection, as well as liver lymphocytes primed by parenteral infection, clearly controlled in vitro intracellular bacterial growth primarily via mechanisms that were not dependent on IFN-gamma activity. Thus, our results indicate functional similarities between immune T cells residing in spleens, livers, and lungs of LVS-immune mice.

Adjuvant interferon gamma in patients with pulmonary atypical Mycobacteriosis: a randomized, double-blind, placebo-controlled study

BACKGROUND

High antibiotic resistance is described in atypical Mycobacteriosis, mainly by Mycobacterium avium complex (MAC).

METHODS

A randomized, double-blind, placebo-controlled clinical trial was carried out in two hospitals to evaluate the effect of interferon (IFN) gamma as immunoadjuvant to chemotherapy on patients with atypical mycobacteria lung disease. Patients received placebo or 1 x 106 IU recombinant human IFN gamma intramuscularly, daily for one month and then three times per week up to 6 months as adjuvant to daily oral azithromycin, ciprofloxacin, ethambutol and rifampin. Sputum samples collection for direct smear observation and culture as well as clinical and thorax radiography assessments were done during treatment and one year after. Cytokines and oxidative stress determinations were carried out in peripheral blood before and after treatment.

RESULTS

Eighteen patients were included in the IFN group and 14 received placebo. Groups were homogeneous at entry; average age was 60 years, 75% men, 84% white; MAC infection prevailed (94%). At the end of treatment, 72% of patients treated with IFN gamma were evaluated as complete responders, but only 36% in the placebo group. The difference was maintained during follow-up. A more rapid complete response was obtained in the IFN group (5 months before), with a significantly earlier improvement in respiratory symptoms and pulmonary lesions reduction. Disease-related deaths were 35.7% of the patients in the placebo group and only 11.1% in the IFN group. Three patients in the IFN group normalized their globular sedimentation rate values. Although differences in bacteriology were not significant during the treatment period, some patients in the placebo group converted again to positive during follow-up. Significant increments in serum TGF-beta and advanced oxidation protein products were observed in the placebo group but not among IFN receiving patients. Treatments were well tolerated. Flu-like symptoms predominated in the IFN gamma group. No severe events were recorded.

CONCLUSION

These data suggest that IFN gamma is useful and well tolerated as adjuvant therapy in patients with pulmonary atypical Mycobacteriosis, predominantly MAC. Further wider clinical trials are encouraged.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN70900209.

Apoptosis of CD4+ and CD8+ T cells during experimental infection with Mycobacterium avium is controlled by Fas/FasL and Bcl-2-sensitive pathways, respectively

Both CD4+ and CD8+ T cells from mice infected with Mycobacterium avium suffered a high rate of apoptosis, beginning with the onset of the immune response and culminating in the loss of T cells from the tissues and loss of IFN-gamma production. Fas expression increased over the course of infection on both T cell populations, as did their susceptibility to the induction of apoptosis in vitro by anti-Fas mAb. Nevertheless, although the rate of apoptosis among CD4+ T cells from infected mice was reduced to normal levels in lpr mice with a defective Fas, CD8+ T cells were unaffected, implying that Fas/FasL interaction was not important in these cells in vivo. Conversely, over-expression of B-cell lymphoma-2 (Bcl-2), which is known to protect T cells from apoptosis signalled through the TNF receptor or due to the withdrawal of cytokines, totally protected CD8+ T cells from infected mice but had no effect on CD4+. It is of interest that these two contrasting pathways of T-cell apoptosis operate at the same time during a single infection.

Mycolactone-mediated inhibition of tumor necrosis factor production by macrophages infected with Mycobacterium ulcerans has implications for the control of infection

The pathogenicity of Mycobacterium ulcerans, the agent of Buruli ulcer, depends on the cytotoxic exotoxin mycolactone. Little is known about the immune response to this pathogen. Following the demonstration of an intracellular growth phase in the life cycle of M. ulcerans, we investigated the production of tumor necrosis factor (TNF) induced by intramacrophage bacilli of diverse toxigenesis/virulence, as well as the biological relevance of TNF during M. ulcerans experimental infections. Our data show that murine bone marrow-derived macrophages infected with mycolactone-negative strains of M. ulcerans (nonvirulent) produce high amounts of TNF, while macrophages infected with mycolactone-positive strains of intermediate or high virulence produce intermediate or low amounts of TNF, respectively. These results are in accordance with the finding that TNF receptor P55-deficient (TNF-P55 KO) mice are not more susceptible than wild-type mice to infection by the highly virulent strains but are more susceptible to nonvirulent and intermediately virulent strains, demonstrating that TNF is required to control the proliferation of these strains in animals experimentally infected by M. ulcerans. We also show that mycolactone produced by intramacrophage M. ulcerans bacilli inhibits, in a dose-dependent manner, but does not abrogate, the production of macrophage inflammatory protein 2, which is consistent with the persistent inflammatory responses observed in experimentally infected mice.

Pathogenesis of Mycobacterium avium infection: typical responses to an atypical mycobacterium?

Studying infections with Mycobacterium avium in mouse models has allowed the dissection of the antimycobacterial pathways of the mammalian host. Whereas the paradigm of cell-mediated immunity to intracellular pathogens has been confirmed, namely with regard to the pivotal roles of CD4+ T cells, macrophages, and the IL12-IFNgamma cytokine axis, atypical features have been uncovered such as the resistance to NO, the involvement of minor players in the induction of type 1 protective immunity (such as TLR2, CD40, and CD30), and the development of immunopathology during the infection with highly virulent strains such as the development of caseous necrosis of granulomas or the progressive emergence of severe lymphopenia.

CD4+Cells Play a Limited Role in Murine Lung Infection withMycobacterium kansasii

Mycobacterium kansasii has emerged as an important nontuberculous mycobacterium that can cause severe infection in the immunocompromised host, especially in human immunodeficiency virus-infected patients. However, little is known about the pathogenesis of this infection. Because patients suffering from M. kansasii infection are severely compromised in their cellular immune response, we studied the course of infection in CD4+ cell knockout (KO) mice. Wild-type (WT) mice and CD4+ KO mice were infected with 10(5) cfu of M. kansasii. Although previously shown to be susceptible to Mycobacterium tuberculosis infection, CD4+ KO mice demonstrated no impairment in clearing infection with M. kansasii when compared with WT animals, despite reduced pulmonary inflammation (reduced granuloma formation and lymphocyte infiltration in the lungs). Pulmonary IFN-gamma levels and M. kansasii-induced IFN-gamma production by splenocytes from infected animals were reduced in CD4+ KO mice, confirming that these mice were defective in the M. kansasii-specific T helper cell type 1 immune response. Furthermore, mice deficient for IFN-gamma, IL-12p35, IL-12p40, or IL-18 also displayed a normal host defense against pulmonary infection with M. kansasii. These data suggest that CD4+ cells, IFN-gamma, and an intact T helper cell type 1 response play a limited role in protective immunity against pulmonary M. kansasii infection.

Infection with Mycobacterium ulcerans induces persistent inflammatory responses in mice

Buruli ulcer (BU) is a devastating, necrotizing, tropical skin disease caused by infections with Mycobacterium ulcerans. In contrast to other mycobacterioses, BU has been associated with minimal or absent inflammation. However, here we show that in the mouse M. ulcerans induces persistent inflammatory responses with virulence-dependent patterns. Mycolactone-positive, cytotoxic strains are virulent for mice and multiply progressively, inducing both early and persistent acute inflammatory responses. The cytotoxicity of these strains leads to progressive destruction of the inflammatory infiltrates by postapoptotic secondary necrosis, generating necrotic acellular areas with extracellular bacilli released by the lysis of infected phagocytes. The necrotic areas, always surrounded by acute inflammatory infiltrates, expand through the progressive invasion of healthy tissues around the initial necrotic lesions by bacteria and by newly recruited acute inflammatory cells. Our observations show that the lack of inflammatory infiltrates in the extensive areas of necrosis seen in advanced infections results from the destruction of continuously produced inflammatory infiltrates and not from M. ulcerans-induced local or systemic immunosuppression. Whether this is the mechanism behind the predominance of minimal or absent inflammatory responses in BU biopsies remains to be elucidated.

CCL5-CCR5 interaction provides antiapoptotic signals for macrophage survival during viral infection

Host defense against viruses probably depends on targeted death of infected host cells and then clearance of cellular corpses by macrophages. For this process to be effective, the macrophage must presumably avoid its own virus-induced death. Here we identify one such mechanism. We show that mice lacking the chemokine Ccl5 are immune compromised to the point of delayed viral clearance, excessive airway inflammation and respiratory death after mouse parainfluenza or human influenza virus infection. Virus-inducible levels of Ccl5 are required to prevent apoptosis of virus-infected mouse macrophages in vivo and mouse and human macrophages ex vivo. The protective effect of Ccl5 requires activation of the Ccr5 chemokine receptor and consequent bilateral activation of G(alphai)-PI3K-AKT and G(alphai)-MEK-ERK signaling pathways. The antiapoptotic action of chemokine signaling may therefore allow scavengers to finally stop the host cell-to-cell infectious process.

CD4+ T cells but Not CD8+ or gammadelta+ lymphocytes are required for host protection against Mycobacterium avium infection and dissemination through the intestinal route

Disseminated Mycobacterium avium infection is common in AIDS patients that do not receive anti-AIDS therapy and in patients for whom therapy fails. M. avium is commonly acquired by ingestion, and a large number of AIDS patients have M. avium in their intestinal tracts. To better understand the dynamics of the infection in patients with AIDS, we studied orally infected mice. To determine if immunocompetent mice challenged orally with M. avium can develop protection against the infection, and if so, which cell population(s) is responsible for the protection, we exposed wild-type as well as CD4(-/-), CD8(-/-), and gammadelta(-/-) knockout mice to low concentrations of M. avium strain 101 given orally, followed by treatment with azithromycin. After 1 month, the mice were challenged with kanamycin-resistant M. avium 104. Only CD4(+) T cells appeared to be required for protection against the second challenge. Both CD4(+) and CD8(+) T cells produced comparable amounts of gamma interferon after the first exposure to the bacterium. Tumor necrosis factor alpha was elevated in CD4(+) T cells but not in CD8(+) T cells. Following exposure to a small inoculum of mycobacteria orally, wild-type mice did not develop disseminated infection for approximately 4 months, although viable bacteria could be observed in the mesenteric lymph nodes. The ingestion of small numbers of M. avium cells induces a protective immune response in the intestines against subsequent infection. However, the bacteria remain viable in intestinal lymph nodes and might disseminate later.

Bystander activation of CD8+ T lymphocytes during experimental mycobacterial infection

Infection of C57BL/6 mice with Mycobacterium avium leads to the activation of both CD4+ and CD8+ gamma interferon (IFN-gamma)-producing T cells, although the CD8+ cells play no role in protection against infection. Using transfer of different lines of transgenic T cells with T-cell receptors (TCRs) which recognize irrelevant antigens, we show here that transferred CD8+ T cells from two of the three lines were activated to the same degree as the host cells, suggesting that the majority of the IFN-gamma-producing CD8+ T cells of the host represented bystander activation. The third line, specific for the male HY antigen, showed no activation. Activation required the participation of the CD28 coreceptor on T cells and was unaffected by the removal of CD44(hi) (memory phenotype) T cells. The transferred CD8+ T cells proliferated in vivo, although this was not essential for IFN-gamma production. Taken together, these data are highly reminiscent of homeostatic proliferation of TCR transgenic T cells upon transfer to lymphopenic hosts, and suggest low-affinity stimulation through the TCR, possibly by self peptides. The findings are discussed in relation to homeostatic proliferation and their significance in the possible induction of autoimmune disease.

Susceptibility of mice deficient in the MHC class II transactivator to infection with Mycobacterium tuberculosis

Major histocompatibility complex (MHC) class II antigen presentation and subsequent CD4+ T-cell activation are critical for acquired immunity to Mycobacterium tuberculosis infection. MHC class II gene expression is primarily controlled by the master transactivator CIITA protein. Without functional CIITA protein, MHC class II expression is lost, impairing immune responses and increasing susceptibility to infection. In this study, we compared protective immune responses of CIITA-deficient mice and wild-type C57BL/6 controls with low dose aerosol M. tuberculosis infection. After aerogenic challenge, CIITA-/- mice failed to limit mycobacterial growth (2.5 and 2.0 log10 > WT lung and spleen CFUs, respectively, at day 58). Lung histopathology involved extensive necrosis, severe pneumonitis and overwhelming inflammation in the gene knockout mice. Mean survival time for CIITA-/- mice was significantly reduced (57 versus >300 days for WT). This extreme sensitivity to tuberculous infection was largely attributed to the absence of CD4+ cells. Flow cytometric studies detected virtually no CD4+ cells in CIITA-/- mouse spleens after infection versus elevated numbers in WT spleens. Failed CD4+ T-cell expansion markedly reduced interferon-gamma (IFN-gamma production in CIITA-/- mice versus WT controls. These results suggest the necessity of a functional CIITA pathway for controlling tuberculous infections and that interventions targeting CIITA expression may be useful antimycobacterial therapeutics.

Generalized immunological decline during long-term experimental infection with Mycobacterium avium

Terminal loss of immune responsiveness in C57BL/10 mice intranasally infected with Mycobacterium avium was observed in both spleen and lung. It was nonspecific and related to the duration of infection, not the age of the mice. While there was loss of total T cells, the remaining cells were less efficient at gamma interferon production.

In vitro responses to purified protein derivate of caprine T lymphocytes following vaccination with live strains of Mycobacterium avium subsp paratuberculosis

Live attenuated vaccines provide protection against intestinal lesions in goats infected with Mycobacterium avium subsp. paratuberculosis. To examine the role of different T lymphocyte subsets in the development of this protective immunity, CD4(+), CD8(+) and gamma delta T cell receptor (TCR)(+) cells from peripheral blood of goat kids vaccinated with live attenuated strains of M. a. paratuberculosis were studied. After in vitro stimulation with purified protein derivate, the expression of gamma-interferon (IFN-gamma) and the activation marker interleukin-2 receptor (IL-2R) was analysed by flow cytometry. A depletion experiment was performed, where the phenotypes and IL-2R expression was studied after stimulation of cultures depleted of a T lymphocyte subpopulation. Close to all of the IFN-gamma producing cells were of the CD4(+) subset, while only a small number were CD8(+) cells. The gamma delta TCR(+) cells were highly activated, but did not produce IFN-gamma after in vitro stimulation. Depletion of CD4(+) cells lead to a decrease in the percentage of total gamma delta TCR(+) cells and gamma delta TCR(+)IL2-R(+) cells. Removing the gamma delta TCR(+) cells increased the relative numbers of CD4(+), but not the CD4(+)IL-2R(+) cells. Insight into the in vitro recall responses of T cell subsets from animals vaccinated with live paratuberculosis vaccines is essential in the development of more efficient vaccines.

Exposure of BALB/c mice to low doses of Mycobacterium avium increases resistance to a subsequent high-dose infection

BALB/c mice exposed intranasally (i.n.), intradermally (i.d.) or intraperitoneally (i.p.) to low doses of Mycobacterium avium (20 c.f.u. at three different times two weeks apart) showed an increased resistance to a subsequent high-dose (10(5) c.f.u.) infection. I.n.-exposed mice had few mycobacteria in the tissues (>100 c.f.u.) and showed an expansion of CD4(+) T cells associated with overproduction of IL-12 and IFN-gamma, but not IL-4 and IgG antibodies. Parenterally (i.p. and i.d.) exposed animals showed c.f.u. numbers higher than i.n.-exposed mice, together with overproduction of IL-12, IFN-gamma and IL-4 in the case of i.p.-exposed mice, and of IL-12, IFN-gamma and IgG2a and IgG1 antibodies in the case of i.d.-exposed mice. Low-dose exposures were not contained by athymic BALB/c nude mice; however, naive nude mice reconstituted with i.n.-primed CD4(+) T cells of BALB/c mice were protected against high-dose infection, indicating that CD4(+) T cells are essential to control even low-dose infections by M. avium. Overall, these data suggest that continuous i.n. exposure to M. avium doses commonly found in the environment may play a role in determining the natural resistance of normal hosts against this organism.

Shifts of T4/T8 T lymphocytes from BAL fluid and peripheral blood by clinical grade in patients with pulmonary tuberculosis

OBJECTIVES

We investigated the shifts of T4/T8 lymphocytes from BAL fluid (BALF) and peripheral blood by the clinical grade of pulmonary tuberculosis (TB), which is determined by factors such as extent of pulmonary involvement, fever, and loss of body weight.

MATERIALS AND METHODS

In order to explore these questions, BALF was collected from 45 patients presenting with active pulmonary TB and 14 healthy control subjects. The percentages for T-lymphocyte subpopulations, including CD4(+), CD8(+), and CD3(+) T cells, were measured using two-color flow cytometry.

RESULTS

A higher percentage of CD3(+)CD4(+) T lymphocytes, with a relatively lower percentage of CD3(+)CD8(+) T lymphocytes, was revealed for the patients with a higher grade of pulmonary TB, compared to patients with a lower grade of pulmonary TB, resulting in an increased BALF C4(+)/CD8(+) ratio. By contrast, a higher percentage of CD3(+)CD8(+) T lymphocytes with a relatively low percentage of CD3(+)CD4(+) T lymphocytes was demonstrated for these patients with a higher grade of pulmonary TB, resulting in a decreased peripheral blood CD4(+)/CD8(+) ratio.

CONCLUSIONS

Our findings suggest that compartmentalization of the CD4(+) T lymphocytes in the infected lungs may occur for patients with higher grades of pulmonary TB.

The involvement of the chemokine receptor CXCR2 in neutrophil recruitment in LPS-induced inflammation and in Mycobacterium avium infection

Knockout mice for CXC receptor 2 (CXCR2) chemokine receptor were used to study the recruitment of neutrophils during acute and chronic inflammatory responses. When treated with lipopolysaccharide (LPS), either intraperitoneally or intratracheally, these animals had a significant reduction in the neutrophil recruitment in the first 24-48 h as compared with control mice. During 15 days of intraperitoneal infection by Mycobacterium avium, the knockout mice showed significantly reduced numbers of neutrophils in the peritoneal cavity as compared with the control mice. In contrast, the recruitment of neutrophils to the lungs during an aerogenic M. avium infection was not affected by the CXCR2 mutation throughout the 60 days of the study. Finally, we could not find any impact of the mutation on the mycobacterial growth of the infected animals. These findings indicate that CXCR2 may be essentially involved in acute inflammatory responses where an early and rapid recruitment of neutrophils is observed.

In vitro and in vivo activities of gatifloxacin against Mycobacterium tuberculosis

Gatifloxacin (GAT) and moxifloxacin (MXF) were evaluated in vitro to determine their activities against Mycobacterium tuberculosis. GAT was subsequently compared in a dose range study to isoniazid (INH) in a murine tuberculosis model. GAT was somewhat less active than INH. GAT and MXF were evaluated in mice infected with M. tuberculosis and were found to have similar activities. GAT was studied alone and in combination with ethambutol, ethionamide (ETA), and pyrazinamide (PZA) and compared to INH and rifampin (RIF). GAT appears to have sufficient activity alone and in combination with ETA with or without PZA to merit evaluation for treatment of tuberculosis.

Interleukin-2 and loss of immunity in experimental Mycobacterium avium infection

Experimental infection of mice with a virulent strain of Mycobacterium avium leads to a slowly progressive disease, which we have previously shown culminates in loss of gamma interferon (IFN-gamma) production by T lymphocytes and death of the animals approximately 40 weeks after infection. Here we investigated the changes in T-cell activation, the production of interleukin-2 (IL-2), and the response to IL-2 throughout M. avium infection as a possible explanation for this loss. We found that there is a steady increase in the percentage of T cells expressing activation markers right to the end of infection. However, in vivo T-cell proliferation, measured as a percentage of CD4(+) and CD8(+) cells incorporating 5-bromo-2'-deoxyuridine, initially increased but then remained constant. In the final stages of infection there was a decline in proliferation of activated (CD62L(-)) T cells. Since IL-2 is a major driver of T-cell proliferation, we asked whether this was due to loss of IL-2 responsiveness or production. However, CD25 (IL-2Ralpha) continued to be highly expressed in the terminal stages of infection, and although IL-2 production declined, addition of recombinant IL-2 to cultures could not rescue the final loss of IFN-gamma production.

Comparative protective effects of recombinant DNA and Mycobacterium bovis bacille Calmette-Guérin vaccines against M. avium infection

A range of strategies are being explored to develop more effective vaccines against mycobacterial infection, including immunization with DNA plasmids encoding single mycobacterial bacterial genes and the use of recombinant live vectors based on the current vaccine, Mycobacterium bovis bacille Calmette-Guérin (BCG). We have compared these two approaches using a model of virulent M. avium infection, and the gene for the immunodominant 35 kDa protein which is shared by M. avium and M. leprae, but absent from BCG. Recombinant BCG over-expressing the M. avium 35 kDa protein (BCG-35) induced strong antigen-specific proliferative and interferon-gamma (IFN-gamma)-secreting T cell responses. These were comparable to those induced by a single immunization with a plasmid expressing the same antigen (DNA-35); however, repeat DNA-35 immunization evoked the strongest IFN-gamma release. Immunization with BCG-35 significantly reduced the growth of virulent M. avium, although this effect was similar to that induced by wild-type BCG. Immunization with DNA-35 resulted in significantly greater (2 x log(10)) reduction in the growth of M. avium. Prime-boost strategies combining DNA-35 and BCG-35 increased the protective effect above that achieved by BCG-35, but they were not more protective than DNA-35 alone. Therefore, recombinant BCG-35 and BCG induced similar levels of protection in this model, and maximal protection against M. avium infection was attained by immunization with DNA encoding the 35 kDa protein.

Molecular and immunological characterization of Mycobacterium avium 65 kDa heat shock protein (Hsp65)

The heat shock protein Hsp65 has been characterized previously in several mycobacterial species. This is the first report of the complete sequence of the coding region of the Mycobacterium avium homologue. The sequence was highly homologous to the Hsp65 of other mycobacterial species, as well as being related closely to the murine and human homologues. Recombinant Hsp65 (rHsp65) was expressed in Escherichia coli to high levels and the recombinant protein tested for its immunogenicity in a murine model of M. avium infection. Although mice infected with M. avium produced antibodies that reacted with rHsp65, they showed low proliferative T-cell responses and no cytokine production in response to the same antigen. However, immunization with rHsp65 in the adjuvant dimethydioctadecylammonium bromide (DDA), induced T cells that responded to native Hsp65 with proliferation and IFN-gamma production, indicating that the recombinant and native forms of the protein were antigenically similar. Therefore, the findings indicate that Hsp65 is not a dominant T-cell antigen during M. avium infection.

Endogenous inhibition of antimycobacterial immunity by IL-10 varies between mycobacterial species

Interleukin (IL)-10 is an immunoregulatory cytokine that inhibits both Th1-like T cell responses and macrophage activation. Deficiency of IL-10 has been associated with increased Th1-like CD4+ T-cell responses and increased clearance of some intracellular pathogens, however, its role in mycobacterial infections is controversial. In order to examine the effects of mycobacterial virulence on the outcome of infection we compared infection with Mycobacterium avium and virulent Mycobacterium tuberculosis in C57Bl/6 IL-10-/- mice. M. avium infection in IL-10-/- mice resulted in sustained increases in interferon (IFN)-gamma-secreting T-cell responses and was associated with the increased clearance of M. avium from the liver and lung. By contrast, M. tuberculosis infection in IL-10-/- mice led to a transient increase in IFN-gamma T-cell responses at 4 weeks postinfection, with reduced bacterial burden in the lungs. This was not sustained so that by 8 weeks there was no difference to wild-type (WT) mice. In vitro infection of IL-10-/- macrophages with M. avium, but not M. tuberculosis, led to an increased IL-12 production. Therefore, endogenous IL-10 exerts a significant inhibition on specific IFN-gamma T-cell responses to M. avium infection, however, this effect is short lived during the M. tuberculosis infection, and fails to influence the long-term course of infection.

Infection of Mice with Mycobacterium avium Primes CD8+ Lymphocytes for Apoptosis upon Exposure to Macrophages

Mycobacterial infection is associated with granuloma formation in which the presence of apoptosis has been recognized. The role of CD4+ T and CD8+ T cells in host protection against mycobacterial infections has been demonstrated. Previous studies, however, have shown that CD8+ T cells have a limited role in host defense against Mycobacterium avium infection, and we hypothesize that M. avium infection could lead to T cell apoptosis. To investigate this hypothesis, C57BL/6 mice were infected with M. avium strain 101, and the rate of apoptosis of splenic lymphocytes cultured ex vivo with peritoneal macrophages was determined and compared with that of controls. When exposed to infected macrophages ex vivo, splenic lymphocytes from M. avium-infected mice underwent apoptosis, as determined by the TUNEL assay. This increased T cell apoptosis above the control level was observed after 3 weeks but not after only 1 week of infection in mice. No splenic T cell apoptosis was observed when lymphocytes from Mycobacterium smegmatis-infected mice were cultured in the presence of M. smegmatis-infected peritoneal macrophages. Likewise, macrophages infected in vitro with heat-killed M. avium did not trigger T cell apoptosis. Culture of macrophages in different chamber from lymphocytes, separated by a transwell membrane, was not associated with increase of apoptosis compared with uninfected control, suggesting a requirement for direct cell-cell interactions to trigger lymphocyte apoptosis. Using a double staining TUNEL followed by anti-mouse CD4 or anti-mouse CD8 monoclonal antibodies, it was observed that only CD8+ T cells but not CD4+ T cells underwent apoptosis at 3 weeks of infection. In conclusion, M. avium infection in C57/BL6 mice for 3 weeks renders CD8+ T cells prone to apoptosis when exposed ex vivo to macrophages infected with M. avium.

Non-major histocompatibility complex control of antibody isotype and Th1 versus Th2 cytokines during experimental infection of mice with Mycobacterium avium

Infection of different strains of mice with Mycobacterium avium has revealed genetic control of the immunoglobulin isotype induced and of the balance between Th1 and Th2 cytokines. Female BALB/c or C57BL/10 mice were infected intranasally with 10(5) M. avium organisms. The antibody response was measured over 18 weeks by enzyme-linked immunosorbent assay and Western blotting, while numbers of cytokine-producing cells were assessed at 12 to 15 weeks by ELISPOT assay. Upon infection, C57BL/10 mice produced a clear Th1 response with strong gamma interferon (IFN-gamma) production, no interleukin-4 (IL-4), and almost entirely immunoglobulin G2a (IgG2a) antibody. In contrast, BALB/c mice developed T cells producing IL-4, as well as those producing IFN-gamma, while the antibody response was a mixture of IgG1 and IgG2a. Antibodies from BALB/c mice were also able to recognize a greater range of antigens than were C56BL/10 mice. B10D2 mice, which carry the BALB/c major histocompatibility complex haplotype on a C57BL/10 background, followed the C57BL/10 cytokine pattern. Mice infected with Listeria monocytogenes did not show a similar response dichotomy.

Interaction of Mycobacterium avium with human monocyte-derived dendritic cells

The mechanism by which mycobacteria elicit class I-restricted T-cell responses remains undefined because these organisms have been shown to reside exclusively within membrane-bound vesicles in macrophages (Mphi), their primary host cells. We studied the interaction of M. avium with dendritic cells (DC) because they are the most potent antigen-presenting cells and are abundant at M. avium infection sites. We observed that both DC and Mphi, generated from human peripheral blood monocytes by short-term culture, internalized M. avium. The onset of programmed cell death and the percentage of apoptotic cells in infected DC and Mphi were comparable. However, following infection, DC secreted significantly larger amounts of interleukin-12, but not interleukin-1beta, than infected autologous Mphi. Further analysis of infected cells showed that while phagosomes failed to acidify in both M. avium-infected DC and Mphi, bacilli grew more slowly in DC. Electron microscopy studies revealed that M. avium resided within endocytic vacuoles in both cell types. The vacuolar membrane surrounding some bacilli in approximately 10% of the vacuoles in DC possessed several breaks. The importance of this finding will have to be addressed in future studies.

T lymphocytes from granulocyte colony-stimulating factor-/- mice produce large quantities of interferon-gamma in a chronic infection model

Little is known about the role of granulocyte colony-stimulating factor (G-CSF) in the response to chronic bacterial infections. To address this we infected G-CSF knock out (G-CSF-/-) mice with Mycobacterium avium. Infection was not exacerbated in G-CSF-/- mice despite a deficiency in the total bone marrow cells, colony-forming haemopoietic cells, granulocytes and monocyte precursors in the bone marrow. Peritoneal cells from G-CSF-/- produced less nitric oxide (NO) upon culture in vitro with antigen than did wild-type (WT) cells. Unexpectedly, T cells from infected G-CSF-/- mice were able to produce significantly more interferon-gamma (IFN-gamma) than the wild type (WT) controls. T cells from G-CSF-/- mice still produced more IFN-gamma even when in vitro NO production was inhibited, while enzyme-linked immunospot assay (ELISPOT) assays showed more IFN-gamma-producing cells in the G-CSF-/- mice. This was confirmed by intracellular cytokine staining (ICCS), which showed that there were more IFN-gamma producing T cells in vivo in the G-CSF-/- than the WT controls following M. avium infection. It is possible that a deficit of NO in vivo allows T cells to develop a higher IFN-gamma-producing phenotype. Thus we show a novel relationship between G-CSF and IFN-gamma production by T cells revealed in this chronic bacterial infection model.

Infection of B cell-deficient mice with CDC 1551, a clinical isolate of Mycobacterium tuberculosis: delay in dissemination and development of lung pathology

Long-term survival of mice infected with Mycobacterium tuberculosis is dependent upon IFN-gamma and T cells, but events in early phases of the immune response are not well understood. In this study, we describe a role for B cells during early immune responses to infection with a clinical isolate of M. tuberculosis (CDC 1551). Following a low-dose infection with M. tuberculosis CDC 1551, similar numbers of bacteria were detected in the lungs of both B cell knockout (IgH 6-, BKO) and C57BL/6J (wild-type) mice. However, despite comparable bacterial loads in the lungs, less severe pulmonary granuloma formation and delayed dissemination of bacteria from lungs to peripheral organs were observed in BKO mice. BKO mice reconstituted with naive B cells, but not those given M. tuberculosis-specific Abs, before infection developed pulmonary granulomas and dissemination patterns similar to wild-type animals. Further analysis of lung cell populations revealed greater numbers of lymphocytes, especially CD8+ T cells, macrophages, and neutrophils in wild-type and reconstituted mice than in BKO mice. Thus, less severe lesion formation and delayed dissemination of bacteria found in BKO mice were dependent on B cells, not Abs, and were associated with altered cellular infiltrate to the lungs. These observations demonstrate an important, previously unappreciated, role for B cells during early immune responses to M. tuberculosis infections.

Haemopoiesis in mice genetically lacking granulocyte-macrophage colony stimulating factor during chronic infection with Mycobacterium avium

In order to test the role of granulocyte-macrophage colony stimulating factor (GM-CSF) in haemopoiesis during chronic infection, mice with a targeted disruption of the gene for GM-CSF were infected intraperitoneally with the facultative intracellular pathogen, Mycobacterium avium. The bacteria spread to lungs, liver and spleen and persisted for more than 10 weeks at levels between 105 and 106 CFU. Bacterial numbers did not differ significantly between infected GM-CSF-/- and wild-type mice, making this an excellent model in which to study the effects of GM-CSF deficiency on haemopoietic cells without complications of interpretation relating to differences in bacterial load. Haemopoietic colony forming cells (CFC) in the bone marrow of GM-CSF-/- mice before infection were not different from wild-type. However, whereas CFC in wild-type mice increased 1.5-fold with infection, GM-CSF-/- mice were unable to increase their CFC and numbers were significantly lower than in infected wild-type mice. Cells attracted to the peritoneal cavity of the GM-CSF-/- mice following i.p. injection of bacteria were notably lacking in the large, granular macrophages of activated appearance, which were a feature in wild-type mice. Nitric oxide production by peritoneal cells from GM-CSF-/- mice was deficient. Thus, GM-CSF is not critical for haemopoiesis during chronic infection, but in its absence the mice are unable to increase their output of haemopoietic cells and there are deficiencies in macrophage activation.

Survival of mice infected with Mycobacterium smegmatis containing large DNA fragments from Mycobacterium tuberculosis

Mycobacterium smegmatis is typically used as a bacterial host for cloning and expressing single genes or genomic libraries of the human pathogen Mycobacterium tuberculosis. To study virulence of M. tuberculosis, we set out to ask the question, whether a genomic library derived from M. tuberculosis H37Rv confers virulence to the non-virulent M. smegmatis. A representative library from the M. tuberculosis H37Rv genome was generated and transformed into wild-type M. smegmatis. Mice were challenged with recombinant clones by intravenous, aerogenic and intranasal infection. We were unable to detect either growth or persistence of recombinant clones in tissues of infected mice; instead, the infection was cleared. Since the concern that virulent traits might be transferred, bio-safety regulations often require the handling of these experiments at bio-safety Level 3. However, we failed to find any evidence that the M. tuberculosis library confers virulence when expressed in M. smegmatis. We suggest that the results, presented here, should fundamentally alter the containment requirements for similar experiments in the future.

CD4(+) T cell clones producing both interferon-gamma and interleukin-10 predominate in bronchoalveolar lavages of active pulmonary tuberculosis patients

The pattern of cytokine production in T cell clones derived from bronchoalveolar lavages (BAL) of active pulmonary tuberculosis (TB) patients was analyzed in clones obtained by limiting dilution procedures which expand with high efficiency either total T lymphocytes, independently of their antigen-recognition specificity, or Mycobacterium tuberculosis-specific T cells. BAL-derived clones, representative of CD4(+) cells from five patients with active TB, produced significantly higher amounts of IFN-gamma than BAL-derived CD4(+) clones from three inactive TB donors or four controls (with unrelated, noninfectious pathology). Average IL-4 and IL-10 production did not differ significantly in the three groups. Although these data suggest a predominant Th1 response to M. tuberculosis infection in the lungs, the majority of BAL-derived CD4(+) clones produced both IFN-gamma and IL-10 and the percentage of clones with this pattern of cytokine production was significantly higher in clones derived from BAL of active TB patients than from controls. Only rare clones derived from peripheral blood (PB)-derived CD45RO(+) CD4(+) T cells of both patients (nine cases) and controls (four cases) produced both IFN-gamma and IL-10; instead, the IL-10-producing clones derived from PB T cells most often also produced IL-4, displaying a typical Th2 phenotype. Higher average amounts of IFN-gamma and IL-10 were produced by BAL-derived CD8(+) clones of four active TB patients than of four controls, although the frequency of CD8(+) clones producing both IFN-gamma and IL-10 was lower than that of CD4(+) clones. The M. tuberculosis-specific BAL-derived T cell clones from three active TB patients were almost exclusively CD4(+) and produced consistently high levels of IFN-gamma often in association with IL-10, but very rarely with IL-4. Unlike the BAL-derived clones, the M. tuberculosis-specific clones derived from PB CD45RO(+) CD4(+) T cells of three different active TB patients and two healthy donors showed large individual variability in cytokine production as well as in the proportion of CD4(+), CD8(+), or TCR gamma/delta(+) clones. These results indicate the predominance of CD4(+) T cells producing both the proinflammatory cytokine IFN-gamma and the anti-inflammatory cytokine IL-10 in BAL of patients with active TB.

Anergy, IFN-γ Production, and Apoptosis in Terminal Infection of Mice with Mycobacterium avium

We have followed the course of experimental infection of mice with Mycobacterium avium over an extended period, assessing bacterial numbers and T cell responsiveness. When mice were infected intranasally, bacteria spread to the spleen and liver, but remained in highest numbers in the lungs. Both CD4+ and CD8+ T cells, assayed at any time from 6–28 wk after infection, produced IFN-γ. After initial rapid growth, bacterial numbers slowly increased from ∼107 at 6 wk to more than 5 × 108 at 28 wk, indicating that the resistance mechanisms so generated were not adequate to contain the infection. During infection, apoptosis of both CD4+ and CD8+ T cells, measured immediately ex vivo by staining with Annexin V, increased steadily. With some individual exceptions, there was a close correlation between apoptosis of CD4+ cells and level of IFN-γ production by cultured spleen cells. By 34 wk postinfection, there was an abrupt cessation of IFN-γ production. No IL-4 was detected, ruling out a switch to Th2 profile. Subsequently, bacterial numbers increased still further to >5 × 109 per lung, and the mice lost body weight and would have died if not killed for experimental or humane reasons. The possibility that T cells exposed over this prolonged period to extremely high doses of Ag may become tolerant by a process of terminal differentiation is discussed.

Use of recombinant viruses to deliver cytokines influencing the course of experimental bacterial infection

The feasibility of using viral constructs expressing cytokine genes to influence the course of bacterial infection was tested in mice. The mice were first infected with vaccinia or fowlpox viruses expressing the cytokine of interest, then challenged with the facultative intracellular bacterial pathogen Listeria monocytogenes. The course of infection was assessed by subsequent bacterial counts. Expression of IFN-gamma or TNF was protective. Vaccinia virus was more efficient at delivering IFN-gamma-mediated protection than was fowlpox virus, which is unable to proliferate in mammalian cells. The effect of vaccinia-IFN-gamma was more apparent in the liver, where vaccinia proliferates to high titres (> 109), than in the spleen, where only 103 vaccinia were isolated. Vaccinia virus expressing IL-4 exacerbated infection. Interleukin-4 exacerbation was T cell independent and was reflected in the failure of macrophage activation, possibly due to suppression of NK cells, which are a source of IFN-gamma early in infection. The clear indication of protection by some cytokines in this prophylactic model appears to justify further study of the therapeutic effects of cytokine-expressing viruses in chronic bacterial infections, especially where a cytokine defect is suspected.

Host defense against Mycobacterium avium does not have an absolute requirement for major histocompatibility complex class I-restricted T cells

The role of CD8(+) T cells was evaluated in a mouse model of disseminated Mycobacterium avium infection. C57BL/6J and C57BL/6Jbeta2-/- (beta2-/-) mice were infected intravenously, and the number of viable bacteria in each liver and spleen was determined. No significant difference between the number of bacteria in the two strains of mice was observed at 2, 4, 6, and 8 weeks after infection. Histopathological examination of granulomas from C57BL/6J and beta2-/- mice did not show any difference either in the number of organisms per granuloma or in the size of the granulomas. Investigation of the cytokine profile in the spleen demonstrated that the beta2-/- strain of mice produced a significantly lower amount of gamma interferon at 8 weeks after infection and significantly increased concentrations of tumor necrosis factor alpha compared with that from the wild-type mouse. Interleukin-12 and transforming growth factor beta1 levels did not differ between the two strains of mice at 2, 4, 6, and 8 weeks. Although previous work had found that host response against Mycobacterium tuberculosis involves major histocompatibility complex class I-restricted T cells, our results indicate that chronic deficiency of CD8(+) T cells does not lead to a different expression of the disease and that if CD8(+) T cells are involved in the host response, their function can be assumed by other immune cells.

Reactivation of tuberculosis is associated with a shift from type 1 to type 2 cytokines

The pattern of cytokines produced by T cells from mice with latent tuberculosis and during reactivation of tuberculosis was determined. A type 1 cytokine pattern was observed in T cells isolated from the lung of mice with latent disease. Reactivation of mycobacterial growth, by activation of the hypothalamic-pituitary-adrenal (HPA) axis, resulted in a shift from a type 1 to a type 2 cytokine pattern in both CD4 and CD8 T cells. Classification of the T cells based on their differential expression of CD45 and CD44 showed that the phenotypically different populations of CD4 and CD8 cells exhibited a type 1 cytokine pattern at latency and that reactivation of latent tuberculosis was associated with a shift in cytokines produced by these populations to a type 2 cytokine response. Control of mycobacterial growth resulted in a return to the type 1 cytokine pattern found during latent disease.

Cytokine production by CD4 and CD8 T cells during the growth of Mycobacterium tuberculosis in mice

Changes in the pattern of cytokines found in CD4 and CD8 T cells during the growth of Mycobacterium tuberculosis that resulted in the establishment of a latent infection were monitored. Subsets of T cells were identified based on their differential expression of CD45 and CD44 which allowed them to be classified as naive, activated or memory. We found that the T cells in the lung produced a predominantly type 1 cytokine response. The appearance of large numbers of Th1 cells coincided with the establishment of latency. In contrast, the predominant response in the mediastinal lymph node and spleen was a Th2-type response.

Altered T-lymphocyte responsiveness to polyclonal cell activators is responsible for liver cell necrosis in alcohol-fed rats

The role of T-cell activation in alcoholic liver disease was investigated in rats fed alcohol and subsequently exposed to concanavalin A (Con A). Following Con A injection (20 mg/kg body weight), greater increases in liver-to-body weight ratio and ALT levels were observed at 12 and 24 hr in rats fed ethanol, compared with control rats fed sucrose. Furthermore, increases in serum interleukin-6 and tumor necrosis factor-alpha levels were noted in ethanol-fed rats, with maximal levels detected at 4 hr declining thereafter, but remaining above control levels at 24 hr. Analysis of T-cell subpopulations showed an increased percentage of CD4+, CD5+, and CD8+ T cells in blood from all groups, but not in liver perfusate. In contrast, a significant increase in the percentage of activated CD25+ T cells was detected in both blood and liver perfusate from rats fed ethanol even 24 hr after Con A injection. When CD4+ and CD8+ T cells from liver perfusate were cultured in the absence or presence of Con A, an increase in interleukin-6 and tumor necrosis factor-alpha production in supernatants was observed in ethanol-fed rats. In cultures stimulated with Con A, a 2- to 8-fold increase in cytokine production was detected, with intrahepatic CD4+ T cells being the major source. Immunohistological analysis revealed infiltration of CD4+ T cells around portal vein and central vein areas associated with fatty liver and severe hepatic necrosis. The results suggest that alcohol consumption induced a dysregulated T-cell population that mediated hepatic necrosis following polyclonal activation with Con A.

Phenotypic changes in T cell populations during the reactivation of tuberculosis in mice

The phenotypic changes of T lymphocytes during the reactivation of latent Mycobacterium tuberculosis infection by activation of the hypothalamic-pituitary-adrenal (HPA) axis was monitored using flow cytometric analysis. Subsets of CD4+ and CD8+ lymphocyte populations from the lung, spleen and draining lymph nodes of infected mice were identified based on their differential expression of the cell surface antigens CD44 and CD45RB. Latent infection was characterized by an accumulation of both naive, activated and memory CD4 and CD8 T lymphocytes in the lung and mediastinal lymph nodes. No changes were observed in the spleen of mice with latent infection when compared with uninfected mice. Immediately following the activation of the HPA axis, a reduction in all CD4+ and CD8+ T cells in the lung and mediastinal lymph nodes was observed. This correlated with the reactivation of mycobacterial growth. The decrease was transient for memory and naive CD4 and CD8 T lymphocyte populations in the lung. However, the number of naive CD4 and CD8 T lymphocyte populations in the mediastinal lymph node following reactivation was less than that found in mice with latent infection. These data provide the first characterization of T lymphocyte populations which may be functionally involved in the immunological response to HPA axis-induced reactivation of M. tuberculosis infection.

Evidence for a reduced chemokine response in the lungs of beige mice infected with Mycobacterium avium

The basis of the increased susceptibility of beige mice to Mycobacterium avium infections is still not clearly understood. In this study we examined the growth of three virulent strains of M. avium in beige mice and normal C57BL/6 controls. Depletion of natural killer (NK) cells by administration of anti-asialo GM1 antisera did not affect the growth of M. avium in any of the groups of animals. Similarly, interferon-gamma (IFN-gamma) gene-disrupted mice were more susceptible to infection than control mice but the growth of M. avium was not further affected by NK-cell depletion. In terms of effector immunity, beige mice showed enhanced expression of IFN-gamma and tumour necrosis factor-alpha (TNF-alpha) when compared with wild-type C57BL/6 mice. In agreement with these results; I-A and interferon-inducible protein (IP-10) expression was also higher in beige mice than in wild-type animals, as was expression of the chemokines macrophage inflammatory protein-2 (MIP-2) and macrophage chemotactic protein (MCP-1) during latter stages of the infection. However, over the first few weeks of the infection, when the susceptibility of the beige mouse lung first becomes evident, MIP-1 beta and MIP-2 chemokine expression in the lungs was lower in beige mice than in wild-type animals. These data indicate, therefore, that the increased susceptibility of beige mice to M. avium infection in the lung is not due to lack of NK-cell activity, nor can it be explained in terms of the effector cytokine response. Instead, the lower early expression of the neutrophil chemoattractants MIP-1 beta and MIP-2 in the lungs of beige mice tends to suggest that the enhanced susceptibility of these mice to M. avium infection may be due in part to defective recruitment of neutrophils or other cells responsive to these specific chemokines.