Question

6. Describe the four stages of extravasation
7. Describe the function of neutrophils
8. Compare innate and adaptive immunity
9. Describe the importance of dendritic cells in activating the adaptive immune response

Answer 1

Answer :

F) Four stages of extravasation :

Leukocyte extravasation (diapedesis) is the movement of leukocytes from the circulatory system and toward the site of infection or damage. The process takes place in several steps :-

1) Chemoattraction : Upon recognisation of and activation by pathogens, the macrophages in the affected tissue release cytokines and chemokines cause the endothelial cells of blood vessels near the site of infection to express cellular adhesion molecules including selectins.

2) Rolling adhesion : carbohydrate ligands on the circulating leukocytes bind to selectin molecules on the inner wall of the vessels with marginal affinity. This causes leukocytes to slow down and begin rolling along the inner surface of the vessel wall.

3) Tight adhesion : In activated state, integrins bind tightly to complementary receptors expressed on endothelial cells, with high affinity. This causes the mobilisation of leukocytes, which varies in vessels that contain different shear forces of the ongoing blood flow.

4) Transmigration : The leukocyte travels through the interstitium towards the site of injury or infection guided by chemotactic signals.

G) Function of neutrophils :

The primary function of neutrophils is "phagocytosis" which means ingestion and destruction of the microorganisms or foreign particles (when the neutrophils engulf the foreign body, the neutrophilic granules release digestive enzymes into the vacuole containing foreign particle and therefore, the particle is destroyed).

H) Comparison between Innate and Adaptive Immunity:

Innate Immunity :

1 - It refers to a naturally occurring immunity by the genetic constituents and physiology of a person.

2 - Generates a non-specific response.

3 - It is always present in the body

4 - Generates a rapid response.

5 - Example: redness or swelling on the hand caused by white blood cells around a wound.

Adaptive Immunity :

1 - It refers to an acquired immunity, mediated by T cells and B cells and characterised by an immunological memory.

2 - Generates a specific response.

3 - It is only generated in response to exposure to an external factor.

4 - The response is delayed 5-6 days.

5 - Example: Vaccination against a virus.

I) Importance of dendritic cells in activating the adaptive immune response :

Dendritic cells play a main role in initiating adaptive immune responses to pathogens .The dendritic cell receptors sense the environmental stimuli and respond rapidly to both foreign pathogens and danger signals like immune complexes or tissue damage through their capacity to present antigen to T cells in immune-activation or immune-dampening context they can both induce T cell proliferation or lack of activation.