Question

Describe the process of phagocytosis and the materials involved from the endocytotic event, to the eventual exocytotic event. In the case of a phagocytosed pathogen, in which step is the pathogen most likely destroyed?

Answer 1

Solution

There are 5 steps of phagocytosis.

Step 1: Activation of the Phagocyte

• Resting phagocytes are activated by inflammatory mediators such as bacterial products (bacterial proteins, capsules, LPS, peptidoglycan, teichoic acids, etc.), complement proteins, inflammatory cytokines, and prostaglandins.
• As a result, the circulating phagocytes produce surface glycoprotein receptors that increase their ability to adhere to the inner surface of capillary walls, enabling them to squeeze out of the capillary and be attracted to the site of infection

Step 2: Chemotaxis of Phagocytes (for wandering macrophages, neutrophils, and eosinophils)

• Chemotaxis is the movement of phagocytes toward an increasing concentration of some attractant such as bacterial factors (bacterial proteins, capsules, LPS, peptidoglycan, teichoic acids, etc.), complement proteins (C5a), chemokines (chemotactic cytokines such as interleukin-8 secreted by various cells), fibrin split products, kinins, and phospholipids released by injured host cells.

Step 3: Attachment of the Phagocyte to the Microbe or Cell

• Attachment of microorganisms is necessary for ingestion. Attachment may be unenhanced or enhanced.

Step 4: Ingestion of the Microbe or Cell by the Phagocyte

• Following attachment, polymerization and then depolymerization of actin filaments send pseudopods out to engulf the microbe and place it in an endocytic vesicle called a phagosome

Step 5: Destruction of the Microbe or Cell

• Phagocytes contain membranous sacs called lysosomes produced by the Golgi apparatus that contain various digestive enzymes, microbicidal chemicals, and toxic oxygen radicals.
• The lysosomes travel along microtubules within the phagocyte and fuse with the phagosomes containing the ingested microbes and the microbes are destroyed

In 5th step pathogen get destroyed.