harika TUBERCULOSIS PATHOGENESIS seminar.pptx

PATHOGENESIS OF TUBERCULOSIS

1. PATHOPHYSIOLOGY OF TUBERCULOSIS

2. INTRODUCTION: TUBERCULOSIS –AN ANCIENT DISEASE Man may have been affected by it ever since he evolved as a species on this planet . Evidence of the existence of tuberculosis has been found in the bones of pre-historic man, dates back to 8000 B.C Consumption, phythsis,pott’s disease,white plaque were all the terms used for tb throughout history. On march 24 1882, Dr. ROBERT KOCH a german scientist announced the discovery of causative agent, Mycobacterium Tuberculosis.

3. AETIOLOGY: TB caused by MYCOBACTRIUM TUBERCULOSIS COMPLEX. The chief human pathogen includes mycobacterium tuberculosis non motile obligate aerobic catalase producing acid fast bacilli (AFB)

4. Spreads by air containing droplet nuclei expelled when person with active pulmonary TB coughs, sneezes, speaks, or sings. TRANSMISSION :

5. RISK FACTORS : Poverty and over crowding Malnutrition HIV/AIDS infection Alcohol and illict drugs abuse Immunosupression states such as diabetes mellitus, malignancies, chronic debilitating diseases Close contacts of person known or suspected to have TB Health care workers (HCWs) who serve high-risk clients

6. EVENTS FOLLOWING ENTRY OF BACILLI: STAGE 1 : Initial Encounter : phagocytosis of M. tuberculosis by alveolar macrophages and dendritic cells takes place. However , bacilli often evade initial destruction and continue to multiply STAGE 2: Recruitment: Influx of polymononuclear cells (PMN) and monocytes which differentiate into macrophages logarithmic growth of bacilli with little tissue destruction.

7. STAGE 3 : Granuloma Formation : Antigen-specific T cells are recruited to the pathologic site and activate monocytoid cells which differentiate into two types of cells: • Epithelioid cells • Langhan type giant cells leads to granuloma formation thus, infection is walled off from rest of the body Stage 4: Stage of Latency : Granuloma disrupts under conditions of failing immune surveillance and leads to endogenous reactivation of dormant bacilli

8. MTB-> INNATE RESPONSE : + APC: macrophage: presents Ag to MHCii , Dendritic cell: capture and process, migrates to regional LN, presents ag to naïve CD4T cells via TCR-> +CD4T-> ADAPTIVE RESPONSE: CD4T Differentiates to Th1 under influence of IL-12 produced by APCs-> produce IFN- γ and TNF-A-> Granuloma M. Tuberculosis resist bactericidal mechanisms of the macrophage by preventing phagosome -lysosome fusion, thus multiply in the phagosome , and cause macrophage necrosis. The released bacilli multiply extracellularly , are phagocytosed by another macrophage that also fails to control the growth of M. tuberculosis, and likewise are destroyed. The released bacilli are also engulfed by dendritic cells migrate to lymph nodes to prime CD4+ and CD8+ T cells against mycobacterial antigens These primed T cells return to the infection site, guided by chemokines , resulting in the formation of a granuloma, which is comprised of macrophages, T cells, dendritic cells, fibroblasts, endothelial cells, and stromal cells

9. IMMUNITY IN TB INNATE IMMUNITY ACQUIRED IMMUNITY –TH1 RESPONSE

10. INNATE IMMUNITY: Epithelial barriers Phagocytic cells : neutrophils and macrophages mainly NK cells Complement proteins

11. INNATE IMMUNITY: RECONGNITION of pathogen associated molecular patterns by by pattern recognition receptors (PRR) TLRs NOD-like receptors in the cytosol ( NLRs) C-type lectin receptors ( CLRs) RIG-like receptors for viral nucleic acids (RLRs) PHAGOCYTOSIS OR ENGULFMENT of bacilli by mono nuclear cells PHAGOLYSOSOME fusion

12. ENTRY MECHANISM OF TB:

13. ENTRY MECHANISM OF TUBERCULOSIS: Engulfment of opsonized bacilli ( which has preformed antibody elements ) by COMPLEMENT RECEPTORS (CR 1,2,3,4 ) ENGULFMENT of non opsonized bacilli (has terminal mannose moieties) through MANNOSE Receptors Other receptors which play an important role include CD14 receptor and SCAVENGER RECEPTOR type A.

14. Evasion of immune system : PHAGOSOMAL MANIPULATION: Maturition arrest: ManLAM : interferes with the normal signaling pathways required for the maturation of the phagosome via mannose receptor on macrophages Inhibition of RabGTPases : Inhibition of transition of Rab5 to Rab7 on the phagosome membrane, essential for maturation of phagosomes and their fusion with lysosome Lack of acid pH: M. tuberculosis can produce urease, which helps maintain a neutral pH within the phagosome .

15. INEFFECTIVE PHAGOLYSOSOME FORMATION : M. tuberculosis produces proteins that disrupt calcium signaling within the host cell leading to impaired fusion M. tuberculosis produces a lipid phosphatase known as SapM (secreted acid phosphatase of Mtb ), which hydrolyzes PI3P , prevents the recruitment of proteins necessary for the fusion of phagosomes with lysosomes and also involved in maturition

16. Acquired immunity PAMPs of Mtb ->TLR2+->+Dendritic cells->IL-12->Th1 cells Th1-mediated Macrophage Activation and Killing of Bacteria TH1 cells, both in lymph nodes and in the lung, produce IFN- γ

17. IFN- γ –The critical mediator . IFN- γ stimulates Maturition of phagolysosome in infected macrophages Expression of inducible NO synthase: NO+other oxidants-> Reactive nitrogen intermediates: important for killing of mycobacterium Antimicrobial peptide: defensins Autophagy: a process that sequesters and then destroys damaged organelles and intracellular bacteria such as M. tuberculosis.

18. In addition to stimulating macrophages to kill mycobacteria, the TH1 response orchestrates the formation of granuloma and caseous necrosis. Macrophages activated by IFN- differentiate into the “epithelioid histiocytes” that aggregate to form granulomas; some epithelioid cells may fuse to form giant cells. . The granuloma formation walls off tubercle bacilli from the rest of the lung tissue, limits bacterial spread, and provide microenvironment for interactions among macrophages and other cells of the immune system and the cytokines produced by these cells. lhe microenvironment of the granuloma (hypoxia, low pH, presence of nitric oxide and carbon monoxide, etc.) increases the expression of several M. tuberculosis genes involved in dormancy induction The dormant bacilli can inhabit the granuloma during the lifetime of the host, but are able to resuscitate (or germinate) in the event of local immunodepression. The latent infection in a person without overt signs of the disease is indicated by the delayed-type hypersensitivity (DTH) response to purified protein derivative (PPD) prepared from culture filtrates of M. tuberculosis (tuberculin skin test).

19. Granulomatous Inflammation :DAMAGE CONTROL In addition to stimulating macrophages to kill mycobacteria, the TH1 response orchestrates the formation of granuloma and caseous necrosis. Macrophages activated by IFN- γ differentiate into the “ epithelioid histiocytes ” that aggregate to form granulomas; some epithelioid cells may fuse to form giant cells . Activated macrophages also secrete TNF and chemokines , which promote recruitment of more monocytes, laying foundation for formation of granuloma

20. GRANULOMA The granuloma formation walls off tubercle bacilli from the rest of the lung tissue, limits bacterial spread, and It provides microenvironment for interactions among macrophages and other cells of the immune system and the cytokines produced by these cells .

21. GRANULOMA

22. GRANULOMAS DDs:

23. PROGRESSION OF DISEASE This response halts infection in some or may progress due to factors like advancing age, immunosuppression, resulting in caseous necrosis The importance of TNF is underscored by the fact that patients with rheumatoid arthritis who if treated with a TNF antagonist( Etanercept , infliximab, adalimumab , certolizumab , golimumab ) have an increased risk of tuberculosis reactivation. Reactivation/ re-exposure to bacilli in previously sensitized results in rapid mobilization of defense reaction but also increase in tissue necrosis

24. SPECIFIC ROLES OF IMMUNE CELLS AND CYTOKINES: CD4T : Apoptosis of infected macrophages through Fas/Fas ligand interaction, Production of IL-2, TNF-A Induction of macrophages and dendritic cells to produce IL-10, IL12, IL-15 cytokines Activation of macrophage occurs through direct contact via CD-40 ligand The CD4T cells also appear to be critical for the cytotoxic function of CD8+ T cells that is mediated by IL-15. CD4+ T cells can control the intracellular growth of M. tuberculosis by a nitric oxide dependent mechanism that is independent of IFN- production. Thus, the CD4+ T cells, in addition to early production of IFN- appear to have several other secondary functions that are critical in the control of M. tuberculosis infection.

25. 2 . CD8T: The CD8+ T cells, in addition to producing IFN- and other cytokines, may also be cytotoxic for M. tuberculosis-infected macrophages, and thus play an important role in providing immunity to TB. cells can directly kill M. tuberculosis via granulysin , and facilitate the control of both the acute as well as chronic infection. CD8+ T cells also have a role in the control of latent infection.

26. REGULATORY T CELLS : Treg (regulatory) cells are a subset of CD4+ T lymphocytes and constitute 1 to 5% of all circulating CD4+ cells. Their main function is to prevent autoimmunity and reduces excess tissue destruction but also permits persistence of chronic infections They are also involved in suppression of host immunity ? MTB may induce expansion of Treg cells -> delay onset of immunity->permits bacilli replication.

27. CYTOKINES : POSITIVE - TNF alpha,IFN gamma,IL-12 NEGATIVE –IL4,IL5,IL-10,TGF-B IL-4:Responsible for suppression of Th1 response,(supresses ifn gamma), leads to development of severe and disseminated forms of disease TGF beta produced by monocytes and dendritic cells can supress CMI, involved in tissue damage and fibrosis

28. Evasion of immune system Modulation of Antigen Presentation : M. tuberculosis uses specific factors to alter antigen presentation pathways to evade immune detection and elimination by T cells. Cell Wall Factors Involved : ManLAM : Mannose-capped lipoarabinomannan. TDM (Trehalose 6,6’-dimycolate) : Also known as cord factor. 19 kDa Lipoprotein : A specific lipoprotein associated with M. tuberculosis. Downregulation of IFN- γ- Inducible Genes : These factors downregulate genes induced by Interferon-gamma (IFN- γ), which are involved in the antigen presentation process through MHC Class I,II and CD1 molecules. Result of Inhibition : These mechanisms result in the inhibition of antigen presentation, allowing M. tuberculosis to persist inside macrophages and evade immune detection. By using multiple strategies to modulate and inhibit antigen presentation, M. tuberculosis effectively evades the immune system, allowing it to survive and persist within host macrophages.

29. EVASION OF HOST IMMUNE RESPONSE:

30. NATURAL HISTORY OF TB: Most primary tuberculosis infections heal spontaneously In some patients there maybe sequalae to primary tuberculosis infection and in general these tend to conform to a timetable of tuberculosis WALLGREN,described this timetable in swedan in 1948 in the era before chemotherapy or BCG when the majority of cases of tuberculosis occurred in the young

31. WALLGREN’S TIME TABLE 1-2 months: primary complex, tuberculin positivity 3-6 months :MILIARY AND MENINGEAL TB 6-12 months: Pleural involvement (pleural effusion due to seeding of the pleura from a lung focus) 1-2years : cavitation (in young adults the primary disease could progresses, with increasing infiltration and cavitation -> progressive primary disease) 1-5 years: bone and joint TB 5-15 years :genitourinary TB

32. Classification of tb

33. PRIMARY TB: The disease known as tuberculosis is the reaction of the tissues of the human host to the presence and multiplication of M. tuberculosis or bovis. Pathogenesis of tuberculosis is basically dependent upon the interplay between immune response and presence and multiplication of bacilli in the host tissues. When infection with M. tuberculosis takes place in a person or an animal that has had no experience with the tubercle bacillus, it is referred to as primary infection or disease. That means, the first infection with tubercle bacillus is primary infection.

34. PRIMARY TB: FIRST TIME infection with tubercle bacilli Primary TB almost always begins in the lungs. Mostly in distal airspaces of the lower part of the upper lobe or the upper part of the lower lobe (due to abundant aeration), usually close to the pleura. A 1–1.5 cm area of grey-white consolidation emerges at the site of seeding of bacilli, known as the GHON’S FOCUS. The centre of this focus undergoes caseous necrosis

35. At the site of implantation, the first response to the presence of tubercle bacilli is non-specific inflammation with serous exudate and the collection of neutrophils. Within 48 hours (2 days) monocytes and macrophages of local origin can be seen and they increase in numbers. Over the next few days during the second week, macrophage infiltration continues and giant cells begin to form. Then lymphocytes appear but only in small numbers, until sometime in the second month when they suddenly increase in number. The sudden increase appears to coincide with the development of tuberculin sensitivity. From about the end of second week the cells at the centre of tubercle begin to change. Caseation begins and increases as the tubercle grows larger. Thus, the essential elements of tubercle formation are present by the end of second month. The author has come with rule of 2 to briefly remember the series of events in pathogenesis of a tuberculous infection eventually leading to granuloma formation. 2 days—monocytes and macrophages increase in number at the site of infection. 2nd week—macrophage infiltration continues and giant cells begin to form. 2nd month—lymphocytes increase in number, this corresponds to tuberculin sensitivity and tubercle formation. From then onwards the sequence of events varies with the balance of forces. In most individuals the primary complex heals by itself unless the resistance is down because of malnutrition, intercurrent infection or immune deficiency. Then the primary complex may progress and become progressive primary complex. If it heals, as majority of times, it is by fibrosis and later it gets calcified. This change is rarely seen radiologically before one year after infection. Calcification can remain unchanged or may get ossified. Sometimes calcification disappears because of resorption. While changes occur in the primary focus, similar changes with caseation occur in regional lymph nodes and indeed are usually more evident there especially in children. But the process of repair and calcification are essentially the same as in the primary focus itself. The all-important factors are that viable organisms can remain in either site for a life time, so that reactivation can occur at these sites. As tubercle bacilli are disseminated throughout the body, tubercles form and undergo the same sequence of changes. Most heal and disappear but if they do persist and progress, that can give rise to symptoms and clinical signs, which vary with the site of lesion (Fig. 4.4). .

36. ghons complex

37. Ghons focus vs complex(pic) . Tubercle bacilli, either free or within phagocytes, drain to the regional nodes, which also often caseate. This combination of parenchymal lung lesion and nodal involvement is referred to as the Ghon complex (Fig. 5.2). During the first few weeks, there is also lymphatic and hematogenous dissemination to other parts of the body but, no lesion develops in any organ other than lung in immunocompetent person. In approximately 95% of cases, development of cellmediated immunity controls the infection. Hence, the Ghon complex undergoes progressive fibrosis, often followed by radiologically detectable calcification which is named as Ranke complex.

38. histopathology Characteristic inflammatory reaction in tuberculosis is chronic granulomatous inflammation which is characterised by the formation of granulomas (tubercles) with or without caseous necrosis. A granuloma is a microscopic lesion composed of epithelioid cells (modified, activated macrophages), Langhans giant cells (fused epithelioid cells) and rimmed by lymphocytes and fibroblasts. Centre of the granuloma may undergo caseous necrosis (caseating granuloma) or may not show necrosis (noncaseating granuloma) (Figs 5.3 to 5.5). Microscopically, caseous necrosis appears as paucicellular , granular, eosinophilic debris. AFB staining of tissue sections show TB bacilli in 30–40% of cases (Fig. 5.6). Immunocompromised people do not form the characteristic granulomas and their macrophages contain many bacilli.

39. Secondary tb Gross Features The initial lesion is a small focus of consolidation (<2 cm in diameter), within 1 to 2 cm of the apical pleura which is sharply circumscribed firm and grey-white to yellow in colour and have variable degrees of central caseation and peripheral fibrosis.

40. Progressive Pulmonary Tuberculosis This frequently occurs in older adults and immunosuppressed people and is characterised by formation of cavitary lesion in the effected lung most commonly in apex. With adequate treatment the process may be arrested, although healing by fibrosis often distorts the pulmonary architecture. If the treatment is inadequate or if host defences are impaired, the infection may spread via airways, lymphatic channels, or the vascular system

41. Miliary tb (the adjective “miliary” is derived from the resemblance of these foci to millet seeds) Miliary tuberculosis frequently affects other organs like liver, spleen, lymph nodes, meninges, bone marrow, and adrenal glands. Tuberculomas, a term referring to localised conglomerates of necrotising granulomas due to infection by Mycobacterium tuberculosis that present as solitary lung nodules. Miliary pulmonary disease occurs when organisms draining through lymphatics enter the venous blood and circulate back to the lung. xray

42. eptb According to WHO criteria, extrapulmonary tuberculosis is defined as an infection by M. tuberculosis which affects tissues and organs outside the pulmonary parenchyma. It represents between 20 and 25% of all TB cases Extrapulmonary TB (EP-TB) results from the haematogenous and lymphatic spread of M. tuberculosis bacilli. Risk factors involved in the development of EPTB are mainly age, female gender, concurrent HIV infection and comorbidities such as chronic renal disease, diabetes mellitus or immunosuppression. The most common locations are the lymph nodes, pleura and the osteoarticular system. .

43. scrofula Morphology of Tuberculous Lymphadenitis Lymphadenitis is the most frequent presentation of EP-TB, accounting for 30–40% of all EP-TB cases4 and usually involves the cervical region (“scrofula”). In HIV negative individuals, lymphadenitis tends to be unifocal and localised . HIV-positive people, on the other hand, almost always have multifocal disease with systemic symptoms. Gross Features Due to periadenitis lymph nodes get matted and macroscopically appear as large multinodular mass that resembles carcinoma (Fig. 5.11). Cut section shows multiple yellowish foci of caseous necrosis. Histological Features Microscopic examination shows either small epithelioid granulomas or huge epithelioid granulomas (Fig. 5.12) with prominent Langhan giant cells and central caseous necrosis. Granulomas may not be seen in HIV patients particularly in late stages of HIV. pic

44. Pleural tb Morphology of Pleural Tuberculosis With progressive pulmonary tuberculosis, the pleural cavity is invariably involved, and serous pleural effusions, tuberculous empyema, or obliterative fibrous pleuritis may develop. Gross Features In pleural tuberculosis, both parietal and visceral may show small greyish yellow nodules which represent granulomas and pleural thickening (Fig. 5.13). Histological evaluation reveals typical caseating granulomas.

45. Thank you