Pathology of TB: Part 2 - Types of inflammation & pathogenesis and Sequelae

Question 1

granulomatous inflammation

what is granulomatous inflammation?

Answer 1

a form of chronic inflammation characterised by:
- groups of activated macrophages
- groups of T lymphocytes
- necrosis

Question 2

why does the body cause granulomatous inflammation and what is a disadvantage of it

Answer 2

• body’s attempt to section off an offending agent that is difficult to eradicate

Disadvantage:
- often damages healthy tissue

Question 3

why does the body attempt to section off bacteria using granulomatous inflammation in TB?

Answer 3

because mycobacteria can infect and hide in leukocytes like macrophages.

Question 4

what are epithelioid cells in granulomatous inflammation in TB?

Answer 4

activated macrophages that begin resemble epithelial cells

Question 5

what is a feature of epithelioid cells in granulomatous inflammation

Answer 5

the development of abundant cytoplasm

Question 6

what are langhans giant cells in granulomatous inflammation in TB and what is one characteristic of them?

Answer 6

• macrophages that fuse together

1 Characteristic:
- multiple nuclei due to fusion

Question 7

what 2 things do older granulomas have in granulomatous inflammation

Answer 7

• fibroblasts
• collagen

Question 8

why do granulomas have a necrotic core in granulomatous inflammation in TB?

Answer 8

• because there is hypoxia inside the granuloma due to the fibroblasts, collagen, langhans giant cells and epithelioid cells surrounding the core.

Question 9

what type of necrotic core is in the granulomas in TB?

Answer 9

caseous necrotic core

Question 10

what are the 2 key differences between granulomas in TB vs granulomas in other diseases?

Answer 10

Granulomas in TB:

1. TB ONLY has caseous necrotic core
2. has acid fast bacteria

Question 11

Transmission

how can TB be transmitted

Answer 11

1. infected people can project small droplets/ aerosols containing TB in cough
2. this is then inhaled by non-infected individuals and the TB will reach the alveoli

Question 12

what does the waxy outer coating make TB organisms resistant to?

Answer 12

resistant to desiccation (removal of moisture)

Question 13

outline the 4 steps that happen in the first 3 weeks to someone that acquires TB

Answer 13

1. inhaled mycobateria engulfed by macrophages
2. the mycobacteria maipulate endosomes in macrophages to be able to HIDE in macrophages
3. this causes defective phagolysosome formation
4. mycobacteria will then proliferate in the endosomes in macrophages, usually leading to mild flu symptoms

Question 14

outline 6 steps of what happens towards the end of the first 3 weeks of TB infection, regarding steps before granuloma inflammation and the formation of epithelioid macrophages.

Answer 14

1. Macrophages that have phagocytosed mycobacteria drain to lymph nodes and prime lymphocytes, causing T cells to be recruited to the lung

2.antigens from mycobacteria displayed on macrophage surface and presented to T cells.

3. T cells are converted to Th1 cells
4. Th1 cells activate more macrophages for phagocytosis by secreting interferon-𝛄
5. Monocytes are also recruited to release free radicals and Reactive Oxygen species, causing necrosis
6. this causes granuloma inflammation and the formation of epithelioid macrophages

Question 15

what does granulomas bursting cause?

Answer 15

can cause post-primary TB

Question 16

what is the Ghon focus and where is it usually found

Answer 16

• primary lesion of granulomatous inflammation
• usually subpleural (found on outside of lungs)

Question 17

what is a Ghon complex

Answer 17

• this is a Ghon focus with the infection and involvement of adjacent lymphatics and hilar lymph nodes, causing the whole lung lobe to be affected.

Question 18

what is a Ranke complex

Answer 18

when a Ghon’s complex undergoes fibrosis and calcification

Question 19

what happens if the immune system of a person with a TB granuloma deteriorates and what will the TB bacilli do after this?

Answer 19

TB bacilli can be reactivated and break out of the granuloma.

• once reactivated and out, the TB bacilli rapidly and majorly destroy the lung tissue around the granuloma, causing cavitation in the lung tissue (small holes)

Question 20

outline how dissemination can occur in TB and state:
- what happens if the pulmonary vein is involved
- what happens in the pulmonary artery is involved

Answer 20

Dissemination can occur in TB when caseating TB granuloma erodes into lung vasculature

If pulmonary vein involved:
- systemic dissemination to organs like liver, kidney and spleen

If pulmonary artery involved:
- lymph drainage to right side of heart, leading to miliary TB of lung