2. DISCUSSION HEADINGS
• INTRODUCTION
• STAGES OF PATHOGENESIS
• HOST IMMUNE RESPONSE
• INNATE AND ACQUIRED IMMUNITY
• PRO INFLAMMATORY & ANTI INFLAMMATORY
MEDIATORS IN TB
• REFERENCES
3.
4. Route and site of infection
• Mycobacterium tuberculosis is an obligatory aerobic,
intracellular pathogen, which has a predilection for the
lung tissue rich in oxygen supply.
• The tubercle bacilli enter the body via the respiratory
route.
• The bacilli spread from the site of initial infection in the
lung through the lymphatics or blood to other parts of
the body,the apex of the lung and the regional lymph
node being favoured sites.
• Extrapulmonary TB of the pleura, lymphatics, bone,
genito-urinary system,meninges, peritoneum, or skin
occurs in about 15 percent of TB patients.
5. Events following entry of bacilli
Stage1:
• Phagocytosis of M.Tb by Alveolar macrophage
• Destruction of M.Tb,but some evade destruction &
continue to multiply inside them & infect Bystander
macrophages
Stage 2:
• Influx of PMN’s,recruitment of Monocytes,differentiate
into Macrophage,but fail to eliminate completely
• Logarithmic growth of bacilli,little tissue destruction
6. Stage 3:
• Ag specific T-cells are recruited to the site that
activate monocytoid cells & differentiate into
two types of Giant cells
• EPITHELIOID,LANGHANS’ GIANT CELL
• Walling off infection from rest of the body &
prevent dissemination of bacilli.
7. Stage 4:
• Stage of Latency (Granuloma) disrupts under
conditions of failing immune surveillance &
leads to ENDOGENOUS RE ACTIVATION of
dormant foci
• Characterised by CASEATION NECROSIS
8.
9. Binding of M. tuberculosis to
monocytes /macrophages
• Complement receptors (CR1, CR2,CR3 and CR4), mannose
receptors (MR) and other cell surface receptor molecules play an
important role in binding of the organisms to the phagocytes.
• The interaction between MR on phagocytic cells and
mycobacteria seems to be mediated through the mycobacterial
surface glycoprotein lipoarabinomannan (LAM).
• Prostaglandin E2 (PGE2) and interleukin (IL)-4, a Th2-type
cytokine,upregulate CR and MR receptor expression and function
• interferon-g (IFN-g) decreases the receptor expression, resulting
in diminished ability of the mycobacteria to adhere to
macrophages.
• There is also a role for surfactant protein receptors, CD14
receptor7 and the scavenger receptors in mediating bacterial
binding.
11. Phagolysosome fusion
• Phagocytosed microorganisms are subject to
degradation by intralysosomal acidic hydrolases upon
phagolysosome fusion.
• This highly regulated event constitutes a significant
antimicrobial mechanism of phagocytes.
• Prevention of phagolysosomal fusion is a mechanism by
which M. tuberculosis survives inside macrophages.
• mycobacterial sulphatides,derivatives of multiacylated
trehalose 2-sulphate,have the ability to inhibit
phagolysosomal fusion.
• studies demonstrated that M. tuberculosis generates
copious amounts of ammonia in cultures,which is
thought to be responsible for the inhibitory Effect.
14. Reactive oxygen intermediates (ROI)
• Hydrogen peroxide (H2O2), one of the ROI generated
by macrophages via the oxidative burst, was the first
identified effector molecule that mediated
mycobactericidal effects of mononuclear phagocytes.
• M.tuberculosis infection induces the accumulation of
macrophages in the lung and also H2O2 production.
• Similar local immune response in tuberculous ascitic
fluid has also been demonstrated.
• Increased production of hydrogen peroxide by alveolar
macrophages is not specific for TB.
• Moreover, the alveolar macrophages produced less
H2O2 than the corresponding blood monocytes
15. Reactive nitrogen intermediates (RNI)
• Phagocytes upon activation by IFN and TNF
generate NO & related RNI via iNOS2
• 1,25 dihydroxy Vit D3 reported to induce the
expression of NOS2
• High level expression of NOS 2 detected
immunohistochemically in macrophages
obtained by BAL in individuals with active PTB
16.
17. Other mechanisms of growth
inhibition/killing
• IFN and TNF mediated antimycobacterial
effects
• VIT D3 alone or in combination with IFN and
TNF able to activate macrophage to inhibit/kill
M.Tb
18. Macrophage apoptosis
• potential mechanism involved in macrophage
defense against M. tuberculosis is apoptosis or
programmed cell death.
• apoptosis associated with TB is mediated through a
downregulation of bcl-2, an inhibitor of apoptosis
• Within the granuloma, apoptosis is prominent in the
epithelioid cells as demonstrated by condensed
chromatin viewed by light microscopy or with the in
situ terminal transferase mediated nick end labeling
(TUNEL)
• Results in reduced viability of M.Tb
19. Evasion of host immune response by
M.tuberculosis
• Modulation of antigen presentation to avoid elimination by T cells.
• Protein secreted by m. Tuberculosis such as superoxide dismutase
and catalase are antagonistic to ROI.
• Mycobacterial components such as sulphatides, LAM and
PHENOLIC- GLYCOLIPID I (PGLI) are potent oxygen radical
scavengers.
• M.Tuberculosis-infected macrophages appear to be diminished in
their ability to present antigens to CD4+T cells, which leads to
persistent infection.
• Another mechanism by which antigen presenting cells (APCS)
contribute to defective T cell proliferation and function is by the
production of cytokines, including TGF-Β, IL-10 OR IL-6.
• Virulent mycobacteria were able to escape from fused phagosomes
and multiply
21. Innate immune response
• The phagocytosis and the subsequent secretion of IL-12 are
processes initiated in the absence of prior exposure to the
antigen and form a component of innate immunity.
• The other components of innate immunity are
natural resistance associated macrophage protein
(Nramp),neutrophils, natural killer cells (NK) .
• PLASMA LYSOZYME and other enzymes may play an
important role in the first line defense, of innate immunity
to M. tuberculosis.
• The role of CD-1 restricted CD8+ T cells and non-MHC
restricted T cells(γ/δ cell) have been implicated but
incompletely understood.
22. Nramp
• Nramp(SLC11A1) is crucial in transporting nitrite
from intracellular compartments such as the
cytosol to more acidic environments like
phagolysosome, where it can be converted to NO.
• Integral membrane protein,ion transporter family
esp Feᶧᶧ
• Defects in Nramp production increase
susceptibility to mycobacteria.
• NRAMP1 gene might not be associated with the
susceptibility to pulmonary and spinal TB in the
Indian population
23. NEUTROPHILS
• Increased accumulation of neutrophil in the granuloma and
increased chemotaxis has suggested a role for neutrophils.
• At the site of multiplication of bacilli, neutrophils are the
first cells to arrive followed by NK cells, γ/δ cells and α/β
cells.
• There is evidence to show that granulocytemacrophage-
colony stimulating factor (GM-CSF) enhances phagocytosis
of bacteria by neutrophils
• Human studies have demonstrated that neutrophils provide
agents such as defensins, which is lacking for macrophage-
mediated killing.
• neutrophils can bring about killing of M. tuberculosis in the
presence of calcium under in vivo conditions.
24. •
NK CELL
Effector cells of innate immunity.
• Directly lyse the pathogens or can lyse infected monocytes.
• Culture with live m. Tuberculosis brought about the expansion of
NK cells
• During early infection, NK cells are capable of activating
phagocytic cells at the site of infection.
• A significant reduction in nk activity is associated with multidrug
resistant tb (MDR-TB).
• Nk activity in BAL has revealed that different types of pulmonary
tb are accompanied by varying degrees of depression
• Apoptosis is a likely mechanism of NK cytotoxicity. NK cells
produce IFN-g and can lyse mycobacterium pulsed target cells.
• Lowered NK activity during TB infection is probably the ‘effect’
and not the ‘cause’ for the disease
• Augmentation of NK activity with cytokines implicates them as
potential adjuncts to TB chemotherapy.
25. TOLL LIKE RECEPTOR
• Phylogenetically conserved mediators of
innate immunity essential for microbial
recognition on macrophages & dendritic cells
• M. tuberculosis can immunologically activate
cells via either TLR2 or TLR4 in a CD 14-
independent, ligand-specific manner
• TLR 2 – LAM
• TLR 4 – Heat labile factor
• TLR 9 – cpg DINUCLEOTIDES
26. • TLR binds to target
• Coupling of IRAK -1 signalling molecules &
MyD88 (myeloid differentiation) gene
• Translocation of NF κB (transcription factor)
from cytosol to nucleus
• Cytokine production
27. Acquired immune response
• Humoral immune response:
• Since M. tuberculosis is an intracellular
pathogen, the serum components may not get
access and may not play any protective role.
• Although many researchers have dismissed a
role for B cells or antibody in protection
against TB, recent studies suggest that these
may contribute to the response to TB.
28. Cellular immune response
• T CELLS
• M.TB is a classic example of pathogen with a
protective response relying on CMI
• Activated T cells migrate to site of infection
and interact with APC’s.
• Tuberculous Granulomas contain both CD4 &
CD 8 T cells & helps to contain the infection
within Granuloma and prevent reactivation.
29. CD4 T CELLS
• Most important cells in protective response
against M.Tb
Primary effector function - production of IFN γ
& other cytokines to activate Macrophage
Also related to NOS2 expression
Other unknown functions(protective) which
are IFN & NOS2 independent
Target for vaccine design
30. CD 8 T CELLS
• Play in regulating Th1/Th2 balance
• Studies: TB with slow regression was associated
with an ↑ CD 8 T cell in BAL F
Capable of secreting IFN & IL 4 (Mφ activation)
Lysis of infected human dendritic cells & Mφ By
CD8 T cells specific for M.Tb Ag reduces
intracellular bacterial numbers(CTL)
o Killing : Perforin/Granulysin pathway
Attractive vaccine candidate
31. T cell APOPTOSIS
• Attenuation of CMI by inducing T CELL
apoptosis in M.Tb
• Leads to diminished M.Tb stimulated IFN γ &
IL 2 production
• TB infection leads to CD 95 mediated Th1
depletion
33. γ/δ T cells
• Large granular lymphocytes with dendritic
morphology in lymphoid tissue
• Non MHC restricted
• Function as cytotoxic T cells for monocytes
pulsed with mycobacterial antigen.
• Secrete cytokines involved in granuloma
formation.
34. NK T CELLS
• CD 1 molecules are antigen presenting
molecules that present lipids or glycolipids to
T cells.
• Usually found on dendritic cells present in the
lungs.
• Stimulate CD 1 restricted T(NK T cells) in the
granuloma that can have a bystander effect on
infected Mφ.
35. T reg cells
• T cells with suppressing (other T cells) capability
• CD4 cells expressing CD 25
• FOXp3,transcription factor essential for development of T reg cells
(also MARKER)
• CTLA4 expressed on T reg induce negative signalling (contact
dependent CD80/CD86))
• It secrete IL 10,TGF β which supress activated T cells
• It requires
• Expansion & recruitment(CCR1,CCR4) at pathologic sites for the
above actions
• Express TLR2,TLR 4 On its surface
• TLR2 engagement –ELIMINATION → Th1 response
• TLR 4 engagement – EXPANSION →immunosuppression
36. Th1/Th2 dichotomy
• Th1 secrete IL2, IFNγ
Protective role in intracellular infections.
• Th2 secrete IL4, IL5, IL10.
Exert a negative influence on the immune response
IL 12 induce Th1 type response
Th1 type response relate directly to the clinical
manifestations of the disease
Limited TB: alveolar lymphocytosis with high levels of
IFNγ.
Far advanced / cavitary disease : no Th1 response.
37. Proinflammatory Cytokines
TNF Alfa (Stimulation of monocytes, macrophages, and dendritic cells with
mycobacteria or mycobacterial products induces the production of TNF-, a prototype
proinflammatory cytokine)
• TNFα plays a key role in granuloma formation, induces macrophage
activation, and has immunoregulatory properties.
• In tuberculosis patients, TNF- production is present at the site of
disease.
• Systemic spill over of TNF- may account for unwanted
inflammatory effects like fever and wasting. (double edged sword )
• Clinical deterioration early in treatment is associated with a
selective increase of TNFα in plasma , and quick recovery is
associated with a rapid decrease of TNFα in plasma .
• To limit the deleterious effects of TNF α, systemic production of
TNF- is downregulated and soluble TNF- receptors which block
TNF- activity are increased .
• In line with this, the use of potent monoclonal anti-TNF- antibodies
in Crohn’s disease and rheumatoid arthritis has been associated
with increased reactivation of tuberculosis (including miliary and
extrapulmonary disease.
38. IL-1β
• produced by monocytes, macrophages, and
dendritic cells .
• In tuberculosis patients, IL-1β is expressed in
Excess and at the site of disease.
• Acute phase response
• Fever & cachexia
39. IL-6
• IL-6, which has both pro- and anti-inflammatory
properties , is produced early during
mycobacterial infection and at the site of
infection.
Role : inflammation,hematpoeisis,differentiation
of T cells
• IL-6 may be harmful in mycobacterial infections,
as it inhibits the production of TNF- and IL-1.
40. IL 12
• IL-12 is a key player in host defense against M. tuberculosis.
• IL-12 is produced mainly by phagocytic cells(Mφ,DC)
• IL-12 has a crucial role in the induction of IFN-γ production.
• In tuberculosis, IL-12 has been detected in lung infiltrates, in
pleurisy, in granulomas , and in lymphadenitis.
• The expression of IL-12 receptors is also increased at the site
of disease.
• In humans suffering from recurrent nontuberculous
mycobacterial infections, deleterious genetic mutations in the
genes encoding IL-12p and IL-12R have been identified.These
patients display a reduced capacity to produce IFN- γ.
• IL-12 is a regulatory cytokine which connects the innate and
adaptive host response to mycobacteria and which exerts its
protective effects mainly through the induction of IFN-γ
41. IL-18 and IL-15
• IL-18, a novel proinflammatory cytokine which shares many
features with IL-1, was initially discovered as an IFN--inducing
factor, synergistic with IL-12.
• IL-18 also stimulates the production of other proinflammatory
cytokines, chemokines, and transcription factors .
• Also, M. tuberculosis-mediated production of IL-18 by peripheral
blood mononuclear cells is reduced in tuberculosis patients, and
this reduction may be responsible for reduced IFN-γ production .
• IL-15 resembles IL-2 in its biologic activities, stimulating T-cell and
NK-cell proliferation and activation .
• Unlike IL-2, however, IL-15 is primarily synthesized by monocytes
and macrophages
42. IL 2
• Pivotal in generating immune response
• Induce expansion of pool of lymphocytes
• Secreted by CD4 Th1 subtype lymphocytes
• Influence the course of Tuberculosis
43. IFNγ
• The protective role of IFN- in tuberculosis is well
established, primarily in the context of antigen-specific T-
cell immunity.
• Produced by both CD4,CD8 T cells & NK cells
Augment antigen presentation leading to recruitment of
Lymphocytes
potent activator of infected macrophage resulting in lytic
mechanisms
can be used as a surrogate marker of infection with M.
tuberculosis
Ability of cells to respond to this cytokine is more predictive
than the amount.
Severely depressed in far advanced cases of TB
44. Anti-Inflammatory Cytokines
• The proinflammatory response which is
initiated by M. tuberculosis is antagonized by
anti-inflammatory mechanisms
• IL-4, IL-10, and transforming growth factor
beta (TGF β)
45. IL 10
• Produced by Mφ after phagocytosis of M.Tb
• Downregulation of IFN γ,TNFα ,IL 12
• Macrophage deactivation
• Directly inhibits CD4 T cell by inhibiting APC
function of M.Tb infected cells
• M.Tb induced IL 10 suppresses an effective
immune response
46. TGF β
• Produced by monocytes and dendritic cells
after stimulation with M.Tb or LAM
• Inhibits IFN γ production and proliferation
• In Mφ,it antagonises antigen
presentation,proinflammatory cytokine
production & cellular activation
• Involved in TISSSUE DAMAGE & FIBROSIS by
promoting macrophage collagenases and
deposition of collagen matrix
47. IL 4
• Deleterious effects of IL 4 in intracellular
infections including TB ascribed to suppression of
IFN γ & macrophage activation
• Progressive disease & reactivation were asso with
an ↑ IL 4
• Overexpression of IL 4 intensified tissue damage
• Conversely,Inhibition of IL 4 didn’t seem to
promote cellular immunity
• So, IL 4 in TB is subject of controversy !
48.
49. REFERENCES
• TUBERCULOSIS – WILLIAM ROM,STUART GARAY
• TUBERCULOSIS – SURENDRA SHARMA,ALLADI
MOHAN
• IMMUNOLOGY OF TUBERCULOSIS- IJMR
Dr.ALAMELA RAJU,TRC,CHENNAI
• IMMUNOLOGY OF TUBERCULOSIS: FROM
BENCH TO BEDSIDE- RESPIROLOGY JOURNAL
