Tuberculosis I & II

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Questions and Answers

What is the single most important risk factor for development of TB in HIV prevalent areas?

Poverty

Chronic lung disease

Malnutrition

HIV infection (correct)

Mycobacterium Avium Intracellulae is a causative organism for tuberculosis in which type of hosts?

Patients with Diabetes Mellitus

Immunocompetent hosts

Elderly persons

Immunocompromised hosts (correct)

What is the outcome of infection in a previously unexposed, immunocompetent person?

Development of antimycobacterial B cell–mediated immunity

Development of antimycobacterial T cell–mediated immunity (correct)

Development of chronic debilitating illness

Development of chronic lung disease

What type of disease is tuberculosis?

Chronic granulomatous disease Signup and view all the answers

Who are more prone to pulmonary tuberculosis?

Medically and economically deprived persons Signup and view all the answers

What is the typical causative organism for tuberculosis in immunocompetent hosts?

Mycobacterium tuberculosis Signup and view all the answers

What are the socioeconomic factors that predispose to pulmonary tuberculosis?

Poverty, crowding, chronic debilitating illness Signup and view all the answers

What is the leading infectious cause of death worldwide?

Tuberculosis Signup and view all the answers

Which of the following is NOT a risk factor for development of TB?

Wealth Signup and view all the answers

What type of persons are more prone to pulmonary tuberculosis?

All of the above Signup and view all the answers

What is the primary role of T cells in tuberculosis?

To control the host response to the bacteria and development of pathologic lesions Signup and view all the answers

What is the mechanism by which M.tuberculosis enters macrophages?

Endocytosis mediated by several macrophage receptors Signup and view all the answers

What is the result of the fusion of the phagosome and lysosome?

Killing of M.tuberculosis Signup and view all the answers

What is the role of IFN γ in tuberculosis?

To activate macrophages into epithelioid cells that aggregate to form granulomas Signup and view all the answers

What is the result of the activation of macrophages by IFN γ?

Aggregation of epithelioid cells to form granulomas Signup and view all the answers

What is the role of TH1 cells in tuberculosis?

To produce IFN γ and activate macrophages Signup and view all the answers

What is the result of the absence of an effective immune response in tuberculosis?

Progression of the disease Signup and view all the answers

What is the role of TNF in tuberculosis?

To recruit more monocytes Signup and view all the answers

What is the susceptibility of individuals with AIDS to tuberculosis?

More susceptible Signup and view all the answers

What is the role of the NRAMP 1 gene in tuberculosis?

To influence the progression of the disease Signup and view all the answers

Study Notes

Tuberculosis

Tuberculosis is a communicable chronic granulomatous disease and the leading infectious cause of death worldwide.

Causative Organisms

Typical organisms for immunocompetent hosts:
- Mycobacterium tuberculosis
- Mycobacterium bovis
Atypical organisms in immunocompromised hosts:
- Mycobacterium Avium Intracellulae
- Mycobacterium kansasii

Factors That Predispose to Pulmonary Tuberculosis

Medically and economically deprived persons
Poverty, crowding, and chronic debilitating illness
Elderly persons
Patients with:
- AIDS
- Diabetes Mellitus
- Hodgkin Disease
- Chronic lung disease
- Chronic renal failure
- Malnutrition
- Alcoholism
- Immunosuppression
HIV infection is the single most important risk factor for development of TB in HIV prevalent areas.

Pathogenesis

The outcome of infection in a previously unexposed, immunocompetent person depends on the development of antimycobacterial T cell–mediated immunity.
Infection by M.tuberculosis proceeds in steps:
- Entry into macrophage
- Replication in macrophage
- Innate immunity
- The Th1 response
- Th1-mediated macrophage activation and killing of bacteria
- Granulomatous inflammation and tissue damage
M.tuberculosis enters macrophages by endocytosis mediated by several macrophage receptors.
Once inside the macrophage, M.tuberculosis organism replicates within the phagosome by blocking fusion of the phagosome & lysosome.
Multiple pathogen-associated molecular patterns made by M.tuberculosis are recognized by innate immune receptors and initiate and the innate and adaptive immune responses.

Pathogenesis Contd

3 weeks after infection, the tubercle bacilli within the macrophages are transported via lymphatic pathway to the regional tracheobronchial lymph nodes and presented to T lymphocytes.
This induces T cell-mediated delayed hypersensitivity.
TH1 cells produce IFN γ, which activates macrophages into epithelioid cells that aggregate to form granulomas.
Activated macrophages also produce TNF, which recruits more monocytes.
Host susceptibility: AIDS, immunosuppression, and rare inherited mutation of IL-12 receptor result in more prone to severe infection.
In persons with polymorphisms in the NRAMP 1 gene, the disease may progress due to absence of an effective immune response.