Lung macrophages from bacille Calmette-Guérin-vaccinated guinea pigs suppress T cell proliferation but restrict intracellular growth of M. tuberculosis after recombinant guinea pig interferon-gamma activation

Progressive Host-Directed Strategies to Potentiate BCG Vaccination Against Tuberculosis

The pursuit to improve the TB control program comprising one approved vaccine, M. bovis Bacille Calmette-Guerin (BCG) has directed researchers to explore progressive approaches to halt the eternal TB pandemic. Mycobacterium tuberculosis (M.tb) was first identified as the causative agent of TB in 1882 by Dr. Robert Koch. However, TB has plagued living beings since ancient times and continues to endure as an eternal scourge ravaging even with existing chemoprophylaxis and preventive therapy. We have scientifically come a long way since then, but despite accessibility to the standard antimycobacterial antibiotics and prophylactic vaccine, almost one-fourth of humankind is infected latently with M.tb. Existing therapeutics fail to control TB, due to the upsurge of drug-resistant strains and increasing incidents of co-infections in immune-compromised individuals. Unresponsiveness to established antibiotics leaves patients with no therapeutic possibilities. Hence the search for an efficacious TB immunization strategy is a global health priority. Researchers are paving the course for efficient vaccination strategies with the radically advanced operation of core principles of protective immune responses against M.tb. In this review; we have reassessed the progression of the TB vaccination program comprising BCG immunization in children and potential stratagems to reinforce BCG-induced protection in adults.

Rate of recipient-derived alveolar macrophage development and major histocompatibility complex cross-decoration after lung transplantation in humans

Alveolar macrophages (AM) play critical roles in lung tissue homeostasis, host defense, and modulating lung injury. The rate of AM turnover (donor AM replacement by circulating monocytes) after transplantation has been incompletely characterized. Furthermore, the anatomic pattern of recipient-derived lung macrophages repopulation has not been reported, nor has their ability to accumulate and present donor major histocompatibility complex (a process we refer to as MHC cross-decoration). We longitudinally characterized the myeloid content of bronchoalveolar lavage (BAL) and biopsy specimens of lung transplant recipients and found a biphasic rate in AM turnover in the allograft, with a rapid turnover perioperatively, accelerated by both the type of induction immunosuppression and the presence of primary graft dysfunction. We found that recipient myeloid cells with cell surface AM phenotype repopulated the lung in a disorganized pattern, comprised mainly of large clusters of cells. Finally, we show that recipient AM take up and present donor peptide-MHC complexes yet are not able to independently induce an in vitro alloreactive response by circulating recipient T cells.

Innate immune memory of tissue-resident macrophages and trained innate immunity: Re-vamping vaccine concept and strategies

In the past few years, our understanding of immunological memory has evolved remarkably due to a growing body of new knowledge in innate immune memory and immunity. Immunological memory now encompasses both innate and adaptive immune memory. The hypo-reactive and hyper-reactive types of innate immune memory lead to a suppressed and enhanced innate immune protective outcome, respectively. The latter is also named trained innate immunity (TII). The emerging information on innate immune memory has not only shed new light on the mechanisms of host defense but is also revolutionizing our long-held view of vaccination and vaccine strategies. Our current review will examine recent progress and knowledge gaps in innate immune memory with a focus on tissue-resident Mϕs, particularly lung Mϕs, and their relationship to local antimicrobial innate immunity. We will also discuss the impact of innate immune memory and TII on our understanding of vaccine concept and strategies and the significance of respiratory mucosal route of vaccination against respiratory pathogens.

Protective immune mechanisms of Yifei Tongluo, a Chinese herb formulation, in the treatment of mycobacterial infection

Yifei Tongluo (YFTL) is a traditional Chinese medicine (TCM) formulation which has been shown clinical efficacy in treatment of patients with multidrug-resistant tuberculosis in China. However, the underlying mechanisms of the effects of YFTL are lacking. This study investigated the effects of YFTL on immune regulation with a mouse lung infection model with Bacille Calmette-Guérin (BCG). We found that compared with untreated mice, the lung mycobacterial load in YFTL-treated mice was significantly reduced, accompanied by alleviated pulmonary inflammation with reduction of pro-inflammatory cytokines and increase of prostaglandin E2 (PGE2). Flow cytometry analyses showed that Th1 cells were significantly higher in the lungs of YFTL-treated mice at early infection time. The results suggest that YFTL-treatment down-regulates pulmonary inflammation, which facilitates a rapid infiltration of Th1 cells into the lungs. Moreover, the Th1 cells in the lungs were resolved faster at later time concomitant with increased the regulatory T cells (Tregs). The reduction of mycobacterial burden associated with improved tissue pathology, faster Th1 cell trafficking, and accelerated resolution of Th1 cells in the lungs of YFTL-treated mice indicates that YFTL improves mycobacterial clearance by maintaining lung homeostasis and dynamically regulating T cells in the lung parenchyma, and suggests that YFTL can be used as host-directed therapies that target immune responses to mycobacterial infection.

Immune Responses to Bacillus Calmette-Guérin Vaccination: Why Do They Fail to Protect against Mycobacterium tuberculosis?

Mycobacterium tuberculosis (M.tb), the causative agent of tuberculosis (TB), is the current leading cause of death due to a single infectious organism. Although curable, the broad emergence of multi-, extensive-, extreme-, and total-drug resistant strains of M.tb has hindered eradication efforts of this pathogen. Furthermore, computational models predict a quarter of the world’s population is infected with M.tb in a latent state, effectively serving as the largest reservoir for any human pathogen with the ability to cause significant morbidity and mortality. The World Health Organization has prioritized new strategies for improved vaccination programs; however, the lack of understanding of mycobacterial immunity has made it difficult to develop new successful vaccines. Currently, Mycobacterium bovis bacillus Calmette–Guérin (BCG) is the only vaccine approved for use to prevent TB. BCG is highly efficacious at preventing meningeal and miliary TB, but is at best 60% effective against the development of pulmonary TB in adults and wanes as we age. In this review, we provide a detailed summary on the innate immune response of macrophages, dendritic cells, and neutrophils in response to BCG vaccination. Additionally, we discuss adaptive immune responses generated by BCG vaccination, emphasizing their specific contributions to mycobacterial immunity. The success of future vaccines against TB will directly depend on our understanding of mycobacterial immunity.

The Progress of Therapeutic Vaccination with Regard to Tuberculosis

A major problem with tuberculosis (TB) control is the long duration of drug therapy-both for latent and for active TB. Therapeutic vaccination has been postulated to improve this situation, and to this end there are several candidates already in clinical phases of development. These candidates follow two main designs, namely bacilli-directed therapy based on inactivated -whole or -fragmented bacillus (Mycobacterium w and RUTI) or fusion proteins that integrate non-replicating bacilli -related antigens (H56 vaccine), and host-directed therapy to reduce the tissue destruction. The administration of inactivated Mycobacterium vaccae prevents the "Koch phenomenon" response, and oral administration of heat-killed Mycobacterium manresensis prevents excessive neutrophilic infiltration of the lesions. This review also tries to explain the success of Mycobacterium tuberculosis by reviewing its evolution from infection to disease, and highlights the lack of a definitive understanding of the natural history of TB pathology and the need to improve our knowledge on TB immunology and pathogenesis.

Molecular cloning, expression, and in silico structural analysis of guinea pig IL-17

Interleukin-17A (IL-17A) is a potent proinflammatory cytokine and the signature cytokine of Th17 cells, a subset which is involved in cytokine and chemokine production, neutrophil recruitment, promotion of T cell priming, and antibody production. IL-17 may play an important role in tuberculosis and other infectious diseases. In preparation for investigating its role in the highly relevant guinea pig model of pulmonary tuberculosis, we cloned guinea pig IL-17A for the first time. The complete coding sequence of the guinea pig IL-17A gene (477 nucleotides; 159 amino acids) was subcloned into a prokaryotic expression vector (pET-30a) resulting in the expression of a 17 kDa recombinant guinea pig IL-17A protein which was confirmed by mass spectrometry analysis. Homology modeling of guinea pig IL-17A revealed that the three-dimensional structure resembles that of human IL-17A. The secondary structure predicted for this protein showed the presence of one extra helix in the N-terminal region. The expression profile of IL-17A was analyzed quantitatively in spleen, lymph node, and lung cells from BCG-vaccinated guinea pigs by real-time PCR. The guinea pig IL-17A cDNA and its recombinant protein will serve as valuable tools for molecular and immunological studies in the guinea pig model of pulmonary TB and other human diseases.

Guinea pig skin, a model for epidermal cellular and molecular changes induced by UVR in vivo and in vitro: effects on Mycobacterium bovis Bacillus Calmette-Guérin vaccination

Previously, we reported that ultraviolet B-radiation (UVR) suppressed Bacillus Calmette-Guérin (BCG) vaccine-induced resistance to Mycobacterium tuberculosis in guinea pigs (GP). Herein, we investigated the cellular and molecular changes within the irradiated GP epidermis and the in vivo effect of supernatants from UV-irradiated (200 J m(-2)) epidermal cells (UV-sup) on M. bovis BCG vaccination. UVR increased the number of nucleated keratinocytes in the skin, but caused a decrease in the proportions of CD25(+)T cells. In the spleen, UVR resulted in a decrease in the proportions of T-cell subsets including CD25(+)T cells, and major histocompatibility complex (MHC) class II(+) and CD14(+) cells. Similarly, significant up-regulation of several cytokine mRNAs including IL-10 was also observed. Furthermore, UV-sup significantly reduced the MHC class II expression in peritoneal cells and reduced T-cell proliferation to ConA. The proliferation to purified protein derivative (PPD) was restored to normal levels by anti-IL-10 antibody. The UV-sup when injected into BCG-vaccinated GP significantly diminished the skin test response and T-cell proliferation to PPD and up-regulated the expression of IL-10, IL-4, IL-1β and Foxp3 mRNAs in the lymph node or spleen. Thus, whole body UVR induces profound cellular and molecular changes and injection of UV-sup from epidermal cells mimics the effect of whole body UVR in BCG-vaccinated GP.

The in vivo immunomodulatory effect of recombinant tumour necrosis factor-alpha in guinea pigs vaccinated with Mycobacterium bovis bacille Calmette-Guérin

Previous studies from our laboratory demonstrated that treatment in vitro with recombinant guinea pig tumour necrosis factor TNF (rgpTNF)-α-enhanced T cell and macrophage functions. Similarly, injection of Mycobacterium tuberculosis-infected guinea pigs with anti-TNF-α altered splenic granuloma organization and caused inflammatory changes and reduced the cell-associated mycobacteria in the tuberculous pluritis model. In this study, rgpTNF-α was injected into bacille Calmette-Guérin (BCG)-vaccinated guinea pigs to modulate immune functions in vivo. Guinea pigs were vaccinated intradermally with BCG, 2 × 10(3) colony-forming units (CFU) and injected intraperitoneally with either rgpTNF-α (25 µg/animal) or 1% bovine serum albumin (BSA) for a total of 12 injections given every other day. Treatment with rgpTNF-α significantly enhanced the skin test response to purified protein derivative (PPD), reduced the number of CFUs and increased the PPD-induced proliferation in the lymph nodes at 6 weeks after vaccination. The levels of interleukin (IL)-12 mRNA were increased in the lymph node and spleen cells stimulated with PPD. TNF-α treatment induced a decrease in TNF-α, IL-12p40 and IL-10 mRNA levels in peritoneal cells following PPD stimulation while live M. tuberculosis caused an increase in TNF-α mRNA and a decrease in the IL-10 mRNA expression. TNF-α injection also induced an increase in the infiltration of mononuclear cells and in the proportions of CD3(+) T cells in the lymph nodes. These results indicate that rgpTNF-α enhances some aspects of T cell immunity and promotes control of mycobacteria in the tissues. Future studies will address the role of TNF-α in BCG-vaccinated guinea pigs following low-dose pulmonary challenge with virulent M. tuberculosis.

Cloning of guinea pig IL-4: reduced IL-4 mRNA after vaccination or Mycobacterium tuberculosis infection

Interleukin-4 (IL-4), a pleiotropic cytokine produced by T-helper type 2 (Th2) cells, is involved in promoting humoral immune responses, allergic reactions and asthma. Previous studies suggested an important role for IL-4 in susceptibility to pulmonary tuberculosis; however, the role of IL-4 has not been studied in the guinea pig, a highly relevant model for this disease. In the present study, we cloned a cDNA for guinea pig IL-4 and examined, for the first time, mRNA expression by real-time RT-PCR in cultured guinea pig cells. High levels of IL-4 mRNA expression were detected in spleen T cells of naïve animals after in vitro stimulation with PMA plus ionomycin for 4-24 h. The expression of IL-4 mRNA was low in spleen and lymph node cells immunized with ovalbumin (OVA) plus Complete Freund's Adjuvant (CFA) in response to OVA (Th1), but significantly higher in the guinea pigs immunized with OVA plus alum (Th2). BCG vaccination reduced the expression of IL-4 mRNA in both spleen and lung digest cells compared to naïve guinea pigs, while levels of IFN-γ were similar in both groups. Furthermore, lung cells from Mycobacterium tuberculosis-infected guinea pigs stimulated in vitro with PPD or MPT64 showed low levels of IL-4 mRNA expression. Thus, BCG vaccination or M. tuberculosis infection modulates IL-4 mRNA expression in the guinea pig. Cloning of guinea pig IL-4 will allow us to address the role of IL-4 in vaccine-induced resistance to pulmonary TB in a highly relevant animal model.

Neutralization of TNFalpha alters inflammation in guinea pig tuberculous pleuritis

Previously, treatment with anti-gpTNFalpha antibody enhanced TNFalpha mRNA expression in pulmonary granulomas microdissected from non-vaccinated guinea pigs, and modified splenic granuloma architecture. In this study, pleural fluid, cells, and granulomatous tissues were collected 3, 5, and 8 days post-pleurisy induction in guinea pigs treated with anti-gpTNFalpha or normal serum control. Neutralizing TNFalpha reduced the percentage of macrophages in the pleural exudate while increasing the proportions of neutrophils and lymphocytes. Cell-associated mycobacterial loads were increased in guinea pigs treated with anti-gpTNFalpha antibody. Cells from the pleural exudate in both treatment groups at day 3 expressed predominantly TNFalpha and IFNgamma mRNA. By day 5, treatment with anti-gpTNFalpha antibody significantly reduced TNFalpha mRNA and increased TGFbeta and iNOS mRNA expression, a transition which did not occur in the control group until day 8. TNFalpha mRNA overwhelmed the cytokine milieu of microdissected pleural granulomas in the control group at day 3 whereas TNFalpha, IFNgamma, and TGFbeta mRNA dominated the anti-gpTNFalpha-treated group. At day 8, granulomas from the control group began shifting towards an anti-inflammatory profile with increased levels of TGFbeta mRNA. Neutralization of TNFalpha hastened the transition to an anti-inflammatory cytokine response in guinea pig pleural granulomas and exudate cells.

Evolution of foamy macrophages in the pulmonary granulomas of experimental tuberculosis models

The chronic phase of Mycobacterium tuberculosis infection in mouse experimental models is characterized by the accumulation of foamy macrophages (FM)--which shape the outer ring of the granuloma - in the alveolar spaces, as detected in paraffin-embedded tissues stained with hematoxylin-eosin. In this study, the use of semi- and ultra-thin sections offers more detailed information about the origin of FM both in mouse and guinea-pig experimental models. Lipid bodies (LB) are present in macrophages from the beginning of infection and accumulate in the chronic phase. LB progress from an early (ELB) to a late (LLB) stage, defined according to their progressive capacity to generate cholesterol crystals, resembling atherosclerotic lesions. FM arise from massive accumulation of LLB. Electronic microscopy reveals intracellular lipophilic inclusions (ILIs) in those M. tuberculosis bacilli inside FM. It is our hypothesis that the accumulation of lipids in M. tuberculosis concomitant to the establishment of the non-replicating state prepares the bacilli for future reactivation and for facing future stressful environments.

Expression of interferon-gamma and tumour necrosis factor-alpha messenger RNA does not correlate with protection in guinea pigs challenged with virulent Mycobacterium tuberculosis by the respiratory route

Cytokine messenger RNA (mRNA) expression was investigated in the spleen and lung digest cells of bacillus Calmette-Guérin (BCG)-vaccinated and non-vaccinated guinea pigs following low-dose, pulmonary exposure to virulent Mycobacterium tuberculosis. After purified protein derivative (PPD) stimulation, the levels of lung cell interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha) and spleen cell interleukin-12 (IL-12) p40 mRNAs were significantly increased in the non-vaccinated M. tuberculosis-infected guinea pigs compared to the BCG-vaccinated guinea pigs. In contrast, the expression of anti-inflammatory transforming growth factor-beta and IL-10 mRNAs was significantly enhanced in the spleens of BCG-vaccinated animals. Despite the presence of protective cytokine mRNA expression, the non-vaccinated guinea pigs had significantly higher lung and spleen bacterial burdens. In contrast, BCG-vaccinated guinea pigs controlled the bacterial multiplication in their lungs and spleens, indicating that both protective as well as anti-inflammatory cytokine responses are associated with a reduction in bacteria. In addition, lung digest cells from non-vaccinated guinea pigs contained a significantly higher percentage of neutrophils, CD3(+) and CD8(+) T cells, while the percentage of macrophages was increased in the BCG-vaccinated animals. Total and purified lung digest T cells co-cultured with lung macrophages (LMøs) proliferated poorly after PPD stimulation in both non-vaccinated and BCG-vaccinated animals while robust proliferation to PPD was observed when T cells were co-cultured with peritoneal macrophages (PMøs). Macrophages within the lung compartment appear to regulate the response of T cells irrespective of the vaccination status in guinea pigs. Taken together, our results suggest that type I cytokine mRNA expression is not associated with vaccine-induced protection in the low-dose guinea pig model of tuberculosis.

Differential activation of alveolar and peritoneal macrophages from BCG-vaccinated guinea pigs

We compared the effect of BCG vaccination on the mRNA expression of two prototypic cytokines, IL-12 (Type 1) and IL-10 (Type 2), in guinea pig resident alveolar macrophages (AM) or resident peritoneal macrophages (PM). Cells were stimulated with live or heat-killed Mycobacterium tuberculosis, and/or with recombinant guinea pig (rgp) TNF-alpha and/or rgp IFN-gamma. AM from BCG-vaccinated guinea pigs expressed significantly less IL-10 mRNA and more IL-12p40 mRNA compared to AM from naive animals following stimulation with heat-killed mycobacteria. In PM from BCG-vaccinated guinea pigs, IL-12p40 mRNA was significantly up-regulated; however, the level of IL-10 mRNA was not affected by prior vaccination. rgp TNF-alpha or rgp IFN-gamma, both alone and together, induced a significant increase of H(2)O(2) production in PM from BCG-vaccinated animals. MHC class II expression was dramatically up-regulated in PM from BCG-vaccinated animals stimulated with both rgp TNF-alpha and rgp IFN-gamma. The levels of IL-10 and IL-12p40 mRNA were significantly enhanced in PM stimulated with combinations of rgp TNF-alpha and rgp IFN-gamma, and those cells suppressed the intracellular accumulation of viable, virulent M. tuberculosis. BCG vaccination results in the differential activation of guinea pig AM and PM to promote a Type 1 cytokine milieu and control intracellular mycobacteria.