20 Questions
What is the single most important risk factor for development of TB in HIV prevalent areas?
HIV infection
Mycobacterium Avium Intracellulae is a causative organism for tuberculosis in which type of hosts?
Immunocompromised hosts
What is the outcome of infection in a previously unexposed, immunocompetent person?
Development of antimycobacterial T cell–mediated immunity
What type of disease is tuberculosis?
Chronic granulomatous disease
Who are more prone to pulmonary tuberculosis?
Medically and economically deprived persons
What is the typical causative organism for tuberculosis in immunocompetent hosts?
Mycobacterium tuberculosis
What are the socioeconomic factors that predispose to pulmonary tuberculosis?
Poverty, crowding, chronic debilitating illness
What is the leading infectious cause of death worldwide?
Tuberculosis
Which of the following is NOT a risk factor for development of TB?
Wealth
What type of persons are more prone to pulmonary tuberculosis?
All of the above
What is the primary role of T cells in tuberculosis?
To control the host response to the bacteria and development of pathologic lesions
What is the mechanism by which M.tuberculosis enters macrophages?
Endocytosis mediated by several macrophage receptors
What is the result of the fusion of the phagosome and lysosome?
Killing of M.tuberculosis
What is the role of IFN γ in tuberculosis?
To activate macrophages into epithelioid cells that aggregate to form granulomas
What is the result of the activation of macrophages by IFN γ?
Aggregation of epithelioid cells to form granulomas
What is the role of TH1 cells in tuberculosis?
To produce IFN γ and activate macrophages
What is the result of the absence of an effective immune response in tuberculosis?
Progression of the disease
What is the role of TNF in tuberculosis?
To recruit more monocytes
What is the susceptibility of individuals with AIDS to tuberculosis?
More susceptible
What is the role of the NRAMP 1 gene in tuberculosis?
To influence the progression of the disease
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.
This quiz covers the pathogenesis, clinical presentation, and types of pulmonary tuberculosis, including primary and secondary tuberculosis.
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