Question

Describe how microfilaments and microtubules are involved in the phagocytosis and destruction of a pathogen by a macrophage.

Short answer

The plasma membrane of macrophages extends to engulf the pathogen which is due to the remodeling of the microfilaments or actin filaments. Once the phagosome pinches off the plasma membrane and enters the cytoplasm, it is transported via microtubules to lysosomes.

Step-by-step solution

Introduction

Macrophages initiate phagocytosis by forming membrane extensions or pseudopodia that engulf the pathogen to form phagosomes. The phagosomes are internalized, undergo a maturation process, and are transported to fuse with the lysosome to form a phagolysosome. Finally, the ingested pathogen is rapidly degraded by hydrolytic enzymes in the phagolysosome.

Explanation

Macrophages initiate phagocytosis by exhibiting receptors that interact with ligands on the pathogen. This activates a signaling pathway that alters the membrane composition and remodels the microfilaments or the actin cytoskeleton via F-actin polymerization to form membrane protrusions that engulf the pathogen. When F-actin depolymerizes these membrane protrusions curve and fuse at the distal end forming a vesicle that breaks off from the plasma membrane. This vesicle that contains the ingested pathogen is called a phagosome. Once the phagosome is internalized, the microtubules transport them through the cytoplasm to fuse with the lysosome.