M. Tuberculosis and immune responses

In the Name of God

M. Tuberculosis and

immune responses

Presented By : M. Barabadi , S. Keshavarz Shahbaz

Supervised by : Dr. Noorbakhsh

Tehran university of medical science

Outline :• TB history• TB epidemiology• M TB bacteriology• TB clinical features - symptoms and signs - transmission - active vs. latent TB

• Experimental models• Immune response against TB

- Innate immune defense- Adaptive immune defense

• HIV and TB• Difficulties and advantages in TB research• Risk factors




• HIV and TB• Difficulties and advantages in TB reaserch• Risk factors

The pathogen structure:





M. Tuberculosis Characteristics

• Slow-growing• Facultative Intracellular• Gram-positive• Non Spore Forming• Aerobic• Acid-fast bacilli





Spine TB :

Nemhotep,Priest of Amun died about 1000 BCE

Brain TB :

TB Meningitis :

Meningitis TB

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The TB Song.flv









Active vs. latent TB :

Tuberculosis.flv

Active TB :

Active TB:

• Two Forms :1. Primary-progressive TB (more common in

children) :Progress rapidly to active disease

2. Post-primary TB: present after an interval of many years following exposure

Differences :

I. Clinical presentations II. Different temporal pathogenesisIII. Host genetic susceptibilities

Diagnosis :

M.TB visualization using the Ziehl–Neelsen stain :

M. TB bacterial colonies

Isolation and confirmation of TB by culture take up to 6 weeks .

• 2 months after treatment ,the culture from sputum becomes negative. It is the only accepted biomarker but with low sensitivity and modest specificity .

• Confirmation of Diagnosis is necessary Because clinical presentation of TB is nonspecific and overlaps with:

- pneumonia- lung cancer- sarcoidosis

Xpert MTB/RIF automated molecular PCR

• A cartridge-based, automated diagnostic test that can identify MTB and resistance to rifampicin.

• WHO recently endorsed this method.

• It answers in just 2 hour.

Treatment • The treatment is lengthy (a minimum of 6

months)• It requires the use of multiple drugs to prevent

the selection of drug-resistant mutants.

• It is divided into :A. initial intensive phase : to kill actively

replicating bacilliB. continuation phase : to target persisting bacilli

Blood Transcriptional profiling in Active TB:

• In This method we gain an understanding of immune response and potential factor that lead to the pathogenesis of TB

• 393-transcript signature, present in the blood of patients with active TB ,that was absent in most latent individuals and healthy controls.

• transcriptional signature of active TB is dominated by IFN-inducible signature

Detrimental role of Type1 IFN :

• patients with active TB have a prominent type I IFN–inducible gene signature in their blood that correlated with the extent of radiographic disease and diminished upon successful treatment

Active TB heatmap :

Advantage :

• Early change in the blood transcriptional signature --->2 weeks after treatment

• sputum smear ---> atfer2 months of treatment

• sarcoidosis patients have a similarity to M.TB patients :

They have significant overlap in the IFN-inducible genes that leads to similar immune mechanisms of granulomatous.

Latent TB :

Latent TB :

• Most infected individuals are asymptomatic• 5–10% of latent individuals will develop active

TB during their lifetime• individuals who are immunosuppressed,

particularly those with HIV coinfection are in Higher risk

Diagnosis :

• Tuberculin skin test (TST) is common

• TST is more frequently negative in those individuals most at risk of progression to active disease:

a) the young b) the elderlyc) immunosuppressed

False positive TST

• PPD is prepared from culture filtrate of TB• It contains over 200 antigens also found in the

attenuated BCG vaccine and in many environmental non-TB mycobacteria

Therefore TST has limited specificity

IGRAs :• More specific TB antigens :1. early secretory antigen target-6 (ESAT-6)2. culture filtrate protein- 10 (CFP-10) are absent from BCG and most non-TB is used

• Reactivity to these TB antigens is assessed in terms of production of IFN-γ by blood cells using IFN-γ release assays (IGRAs).

• IGRAs is measured by :1. ELISA 2. ELI-SPOT

Heterogeneity of latent TB :





Human TB and experimental animal models :

• The mouse model offers the best tools for the study of the immune response to TB

• Commonly used mouse strains, such as C57BL/6 or BALB/c mice

• Highly susceptible strain : CBA/J, DBA/2, and C3H

• Advantage:• Infected with low dose virulent TB• Disadvantage:• The granulomas are poorly organized and exclusively cellular• They lack fibrosis or hypoxia • The mice ultimately die • lacks the range of latency to active disease

cynomolgus macaque model It is the most commonly used model for studying latent TB The heterogeneous TB experimental model





Immune response in TB :

1. Formation of Granulomas2. Initials events3. MQ apoptosis4. Role of PMN(Neu)

Formation of Granulomas

Tuberculosis Invasion.mp4

• The classical feature of human TB granulomas:

The presence of a necrotic caseous core that is thought to be secondary to cell lysis that results in a central hypoxic environment .

Caseation necrosis :

Granuloma in active & latent TB :

• In latent TB the bacilli reside in the central hypoxic zone in a metabolically altered state

• In active TB they can replicate in peripheral oxygenated areas.

• Are they purely protective for the host or do they promote infection?

• The pathogen may be able to engineer a supportive environment in the granuloma

Granuloma classification in active TB:

1. The classical caseous granuloma :central eosinophilic debris surrounded by macrophages and a layer of lymphocytes

2. The non-necrotizing granuloma: internal core of macrophages and some neutrophils surrounded by a lymphocyte layer

3. The suppurative granuloma: central core of degenerative neutrophils surrounded by macrophages and multinucleated giant cells and an outer envelope of lymphocytes

First line of defence• Influx of phagocytic cells including :1. primarily resident alveolar MQ2. recruited neutrophils and DCs• Escape : TB prevents phagolysosomal fusion

and persist in the phagosome• Immune defense: Opsonization of the bacilli

prior to infection inhibits this blockade of phagolysosomal fusion

Role of MQ :

• Infection of MQ with M.TB can induce:1. necrotic death: allows exit from MQ and

therefore cell-to-cell spread of the bacilli

2. Apoptotic death : is associated with diminished pathogen viability and enhanced immunity

Efferocytosis

• TB –infected MQ are themselves rapidly engulfed by uninfected MQ through a process called efferocytosis , generally regarded as a constitutive housekeeping function of macrophages.

• The type of cell death is regulated by : The lipid mediators include :1. (proapoptotics): eicosanoids , prostaglandin E2

(PGE2) 2. (pronecrotic): lipoxin A4 (LXA4)

• Virulent strains of TB evade innate defense mechanisms of the host by inducing LXA4 and inhibiting PGE2 production

• They lead to MQ necrosis and inhibition of MQ apoptosis, ultimately resulting in mycobacterial spread.

Role of Neutrophils • Lung Neu facilitate activation of naive antigen-specificCD4+

Tcells during M .TB infection.• IT promote an anti–M.TB adaptive immune response by

delivering the bacilli to DCs in a form that makes DCs more effective initiators of CD4+ T cell activation.

• Neu have a protective or detrimental effect during an immune response to TB infection may be determined by:

1. The genetics of the pathogen as well as by the genetics of the host

2. The stage of TB disease3. Tissue environment4. Network of cytokines

Detrimental role of Neu : • Neutrophils are dominant producers of IL-10

in the lung .

• Depletion of neutrophils reduces the lung bacterial load while enhancing IL-6 and IL-17, but not IFN-γ, responses





Innate immune factors :

1. TNF2. Inflammation3. Pattern recognition receptors ,Adaptor

proteins

TNF• Role :1. Formation and maintenance of the integrity of the

granuloma 2. Boosting the intracellular killing of bacilli

• Granuloma formation could occur even in the absence of TNF signaling, but these granulomas were :

• Delayed• More necrotic • With higher bacillary numbers.

Inflammation :

1. Eicosanoids2. Matrix metalloproteinases : MMP-1 and MMP-9 : key collagenase upregulated in patients with TB and associated with increased lung pathology in transgenic mice 3. Vitamin Da pro-hormone that in kidney converts to its active form .Conversion can also occur in granulomatous tissue.

• Vit D3 has regulatory and anti-inflammatory immune effects ,therefore continues to be of potential therapeutic interest.

• Historically ,sunlight exposure and vitamin D were used as treatments for TB.

Pattern recognition receptors and Adaptor proteins :

• Pattern-recognition receptors (PRRs): 1. Toll-like receptors (TLRs)2. C-type lectin receptors (CLRs)including

dectin-1, mannose receptor, and DC-SIGN3. Nod-like receptors (NLRs)

• MyD88 and CARD9 :- master adaptors of TLR - critical for protective immunity to M.TB in mouse models

• TLR2, TLR4, and TLR9 play a role in host recognition of M.TB





Adaptive immune response :

1. T cells2. DC cells3. CD-1 restricted response4. B cell5. Cytokines

DC cell• DCs in lymph nodes from patients with M.TB may themselves

contain M.TB

• Depletion of CD11c+ cells in mice before intravenous infection with M.TB delays the development of CD4+ T cell responses

T cells

• The most important T cells is CD4+ T cells

• CD8+ T cells also contribute to anti-TB immunity by:1. Secreting IFNγ To Activate MQ to Control Infection 2. Secreting products that can directly kill The TB

bacilli.

• However, CD8+ T cells clearly can not compensate for a lack of CD4+ T cells.

CD1-Restricted Responses

• TB contains glycolipid Ag that are presented by The CD1 family molecules

• Glycolipid-reactive T cells play a role in an effective response to TB

• They proliferate and produce IFN-γ in response to TB glycolipids

B cells

• Follicle-like B cell have been observed in the lungs of M.TB patients and in the granulomas of infected mice

• Role :1. moderate inflammatory progression 2. modulating immune activation and

susceptibility to infection by induction of IL-10

IFNγ

• The most invariably detected cytokine at the sites of human TB infection in :

- Lung (most )- bronchoalveolar lavage (BAL) fluid- pleuritis fluid- lymph nodes

IFN-γ-Mediated Killingin MQ :

IFN-γ-inducible molecules include: • iNOS , LRG-47, an IFN inducible GTP-binding

protein

• IFN-γ is also important for endosome maturation and the induction of antimicrobial peptide

Control of Inflammation and CD4+T Cells

• various mechanisms are in place to prevent immunopathology, including:

1. Foxp3+ regulatory T cells2. IL-10 3. PD1 ( expressed by T cells from TB patients)

• PD-L1 is overly abundant in the whole blood of active TB patients

PD1 binded to PDl1---> negative signal chronic infection

PD1 deletion ---- > increase of M.TB-specific CD4+ T cell --- > active TB

• This finding demonstrated the importance of a finely regulated immune response to control disease.

IL-17 :

• Both IFN-γ and IL-17-producing T cells are induced during mycobacterial infection

• IFN-γ serves to limit the IL-17-producing T cell population

• IL-17 can also be produced by γδ T cells and a non-CD4+ CD8+ population .

• Role :- Granuloma formation- Th1 enhancement

Following BCG vaccination with a mycobacterial peptide:

IL-17 is required for the accelerated recruitment of IFN-γ-producing cells to the lung as a result of increased concentrations of the chemokines CXCL9, 10, and 11, which recruit cells to sites of inflammation

IL 23

• Essential for the IL-17 response during TB• Dispensable for protection and antigen-

specific IFN-γ responses if IL-12p70 is available

The double-edged sword of suppressivecytokines in tuberculosis

• IL10

• TH2 cytokine

• Type1 IFN

IL10• An immunosuppressive cytokine induced by TB

for immune evasion • If overproduced, IL-10 can contribute to

chronic infection

• IL-10 was elevated in the lungs , BAL fluid , sputum and serum of active TB patients

• Activation of TLR4 (but not of TLR2) will induce higher levels of IL-10 production by MQ

• Bone marrow–derived Neu infected in vitro or Neu isolated from the lungs of mice challenged with TB produce significant levels of IL-10

Th2 Cytokines

• Chronic worm infection of mice reduces immunogenicity to M.TB and reduce Th1 responses.

• Generally ,Helminthes reduce protective immune responses to M.TB infection.

Type I IFNs

• The type I IFN family of cytokines have pleiotropic effects on the broader immune response

• Role :1. Increases susceptibility to M.TB 2. Suppresses production of host-protective

cytokines including IL-1 and IL-12 following M.TB infection in MQ

3. Induction of the immunosuppressive cytokine IL-10





HIV and TB :

• TB is the most common opportunistic infection worldwide in HIV-1-infected persons

• Antiretroviral therapy (ART) for HIV-1 infection improves immune resistance to TB

• Vitamin D reportedly inhibits HIV-1 and TB infection in MQ through the induction of autophagy.

TB-IRIS

• HIV+ patient ---> immunosuppressed--->ART----> decreased viral load and increased CD4+ T cells ---> sudden over activation of immune system ----> rapid recognition of pathogens in body (like TB ) ----> causes severe systemic inflammatory disease

Outline :• M TB history• M TB epidemiology• M TB bacteriology• TB clinical feature - symptoms - transmission - active vs. latent TB




Outline :• M TB history• M TB epidemiology• M TB bacteriology• TB clinical feature - symptoms - transmission - active vs. latent TB



• HIV and TB• Difficulties and advantages in studying• Risk factors

Reference :

Thanks for your

attention

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M. Tuberculosis and immune responses