The pathophysiology of tuberculosis

Graham Rook Centre for Infectious Disease and International Health Windeyer Institute University College London

g.rook@ucl.ac.uk

Tuberculosis: back to basics Manchester, Thurs 18th November 2004

Primary lesion

Latent TB

Haematogenous spread

Reactivation

In situ PCR

Cavitary TB

Cavities open into bronchi

Cough !

(HIV Stress Poverty Smoking)

Progression

Immunity to M. tuberculosis requires a Th1 response

Th1

Th2

IFN­γ

IL­12

TNF­α

Antigen­ presenting cell

lymphocytes

Infected macrophage

IL­4, IL­5

Th0 Tcy

The paradox

Almost every person or animal who contacts M. tuberculosis rapidly develops a

strong “Th1” response

…..so why does anyone get the disease ??

The problem of The problem of “ “compliance compliance” ”. The patient feels better too soon! . The patient feels better too soon! The Th1 response of the tuberculosis patient fails to eliminate The Th1 response of the tuberculosis patient fails to eliminate the residual bacteria, so chemotherapy must continue 6 the residual bacteria, so chemotherapy must continue 6­ ­12 m 12 m

Chronic skin tuberculosis

Old tuberculin s.c. on the back

Fever, rigors, necrosis and sloughing of the skin lesion, and dangerous necrosis of other lesions in lungs or spine.

24­48 hrs

The The “ “Koch phenomenon Koch phenomenon” ” in man in man

Immunise with killed M. tuberculosis by various protocols

Unimmunised controls

Rank according to tuberculin response

“Koch”

Positive

Negative

Result of intramuscular infection with TB

Negative

MORE susceptible than unimmunised controls

Resistant

Susceptible

Susceptible

The Koch phenomenon is not protective The Koch phenomenon is not protective Wilson et al, 1940, (using about 400 Wilson et al, 1940, (using about 400 outbred outbred guinea pigs) guinea pigs)

Possible strategies of pathogenesis

• Fail to induce the protective response

• Resist the protective immune response

• Induce the protective response….and then corrupt it

? Immunopathology ? More dissemination by coughing

Much of the immune response to M. tuberculosis is involved in immunopathology, not immunity

Kaushal et al (2002) PNAS 99:8330

Wild type (unmodified) strain Knockout gene encoding the SigH transcription factor

• Bacterial proliferation • Massive T cell infiltration • Immunopathology • Death

• Same bacterial proliferation • 90% LESS T cell infiltration • No immunopathology • Survive

• 90% of the T lymphocytes in the lesions do not need to be

there to control bacterial proliferation.

• These unnecessary T lymphocytes cause immunopathology

• How do they do it ?

This immunopathology is deliberately triggered by M. tuberculosis

TNF­α becomes toxic when IL­4 is present in Balb/c mice

Th1

• Activation of macrophages • Infection controlled

Th1+ IL­4

• TNF­α becomes toxic • NECROSIS • Failure to control bacterial growth

TNF TNF­ ­α α

Colony­ forming units (CFU)

Weeks 1 2 3 4 5 6 7……..

log

plateau progressive

Th1 IFN­γ

Th1+ Th2 IFN­γ + IL­4

Toxicity of TNF­α; role of IL­4 ?

TNF­α is toxic in Schistosomiasis and Trichinellosis when IL­4 is present in the Th1­mediated lesions

Ferluga et al (1979) Parasite Immunol 1, 289­294 Wynn, et al., (1995) Nature 376:594­596 Lawrence et al., (1998) Eur. J. Immunol. 28:2672­2684

TNF­α is essential for immunity to human TB, BUT

TNF­α is toxic in progressive TB. This is opposed by thalidomide

Moreira et al. (1993) J. Exp. Med. 177, 1675­1680

The use of IL­4 gene knockout Balb/c mice to look at the role of IL­4 in necrosis and fibrosis in

pulmonary TB

Hernandez­Pando et al (2004) Eur J Immunol 34, 174­183

• Role of IL­4 in necrosis confirmed • What about fibrosis ?

Reduced fibrosis (hydroxyproline) in the lungs of tuberculous mice lacking a functional IL­4 gene

IL IL­ ­4 +/+ 4 +/+ IL IL­ ­4 4 ­ ­/ /­ ­

p<0.005 p<0.005

Collagen (mg)/gm Collagen (mg)/gm dry weight of lung dry weight of lung tissue tissue

0

20

40

60

80

100

120

0 10 20 30

Days since infection

* **

***

***

Hernandez­Pando et al (2004) Eur J Immunol 34, 174­183

IL­ 4 IL­ 4δ2

IL­13

IFN­γ from Th1 cells opposes fibrosis, so why is there fibrosis in TB? The presence of type 2 cytokines explains the major fibrotic component.

Matrix metallo­ proteinase (MMP)­9

Latent TGF­β­binding protein­1 (LTBP)

Latent TGF­β

Active TGF­β

LAP

COLLAGEN and FIBROSIS

cleave

(­)

(+)

(+)

(+) Th2 Th2 Macrophage

Fibroblast

Lee et al., (2001) J. Exp. Med. 194:809­821

Summary of Balb/c mouse data

• Progression after the plateau phase is accompanied by rising IL­4

• An IL­4 response before challenge exacerbates subsequent disease

• IL­4 plays a role in toxicity of TNF­α seen in progressive disease

• IL­4 plays a role in fibrosis

• > IL­4 KO mice have attenuated immunopathology

Hernandez­Pando et al (2004) Eur J Immunol 34, 174­183

Does human tuberculosis resemble that seen in Balb/c mice ?

The presence of IL­4 in human TB has been controversial

IL­4 easily detected by ELISA IL­4 not detected by ELISA; need RT­PCR, or prestimulated cells and FACS

Is high IL­4 in TB patients a feature of developing countries?

Rook, Dheda and Zumla (2004), Vaccine, in press

Geographical variation in tuberculosis, and in the efficacy of BCG vaccine; correlation with IL­4?

• IL­4 easily detected in TB patients (by ELISA) • BCG vaccine fails • High death rates during first 2 months of treatment

• In Europe to detect IL­4 in TB you need ­ RT­PCR or ­ stimulation & FACS

• BCG vaccine protects • Patients usually survive

Does a pre­existing IL­4/IL­5 response predispose to TB in man?

Ordway D et al (2004) Increased IL­4 production by CD8 and γ/δ T

cells in health care workers is associated with the subsequent

development of active tuberculosis. J Infect Dis, 190:756­766.

IL­4+ health care workers develop TB within 2­4 years

Beijing strains induce IL­4 in human monocytes

Manca et al. Infect Immun (2004) 72:5511­4

………..In vitro infection of monocytes with Mycobacterium tuberculosis HN878 and related W/Beijing isolates preferentially induced interleukin­4 (IL­4) and IL­13…………..

Low levels of IL­4δ2 now found in rodents Yatsenko et al Bull Exp Biol Med 2004;137:179

IL­4δ2, competitive antagonist of IL­4 at the IL­4Rα, (but agonist on fibroblasts)

Furnham et al. Splice variants: A homology modeling approach. (2004) PROTEINS: structure, function and

bioinformatics 54:596­608

Increased expression of IL­4δ2 in unstimulated peripheral blood mononuclear cells from Ethiopians with latent TB

Demissie et al (2004) J. Immunol. 172: 6938–6943

(ESAT­6 neg) Not infected

(ESAT­6 pos) Latent infection

Tuberculosis

0 100 200 300

% response normalised to β­actin

M. tuberculosis Th1 FAILED Th1­ MEDIATED IMMUNITY

iNOS

Latent infection

BACTERIAL PROLIFERATION

IMMUNOPATHOLOGY (+TNF­α)

FIBROSIS

Th2­like

IL­ 4 IL­4δ2

+ IL­ 13 & IL­ 5

PROPHYLACTIC VACCINE

THERAPEUTIC VACCINE

Environmental mycobacteria Helminths Other ?

SUMMARY

Rook GAW, Hernandez Pando R, Dheda K, Seah GT. IL­4 in tuberculosis: implications for vaccine design. Trends in Immunology 2004; 25:483­488

Conclusions • M. tuberculosis “deliberately” drives immunopathological mechanisms including the Koch phenomenon

• Immunity to TB requires IL­12, IFN­γ, TNF−α and cytotoxic T cells • Many of the T lymphocytes present in lesions are not needed for immunity; they help drive immunopathology

• Deleting certain genes within M. tuberculosis reduces its ability to drive immunopathology without affecting bacterial replication in the host

• Cavities caused by immunopathology open into the bronchi and enable spread by coughing • Inappropriate Th2 lymphocyte activity is involved in the immunopathology • The presence of inappropriate IL­4 (from Th2 cells) in Th1­mediated granulomata, causes TNF­α to become toxic and to contribute to immunopathology

• IL­4 also helps to drive the fibrosis which characterises TB (IFN­γ inhibits fibrosis) • IL­4 downregulates protective macrophage functions • There is more IL­4 in TB in countries within 30 degrees North or South of the equator • These are the areas where BCG vaccine fails and mortality from TB is high, and background Th2 responses to mycobacterial antigens are high

• People with latent TB who do not progress to active disease have increased expression of an antagonist of IL­4, known as IL­4δ2

• A successful vaccine may need to downregulate the unwanted Th2 (IL­4) component, rather than increasing Th1 which is rapidly evoked byM. tuberculosis anyway