They are the most abundant tissue macrophages since they constitute 80-90% of the body.
They are also known as Kupffer-Borowicz cells or stellate macrophages. They are specialized macrophages located in the liver, which line the walls of the sinusoids that are part of the phagocyte mononuclear system.
Kupffer cells are phagocytic, capable of ingesting other cells and foreign particles. They also store hemosiderin to make it available for the production of hemoglobin, the oxygen transport component of the red blood cell.
The development of Kupffer cells begins in the yolk sac. Primitive macrophages differentiate into fetal macrophages and then enter the bloodstream. After that, they go to the fetus’s liver to become mature cells.
Functions of Kupffer cells
In addition to digestion, detoxification, and storage, the liver can function for immunity through Kupffer cells.
The following are ways how these cells contribute to immune function:
Eliminate protein complexes and small particles of blood:
Together with other cells in the sinusoidal endothelium, they are the first line of defense against pathogens that enter the liver through the portal vein.
This function is essential because the blood that passes through that vein is rich in products from pathogens such as lipopolysaccharides and proteins. These products must be eliminated in the circulation to avoid systemic immune activation.
To capture and digest microorganisms and spent cells:
As macrophages, Kupffer cells can engulf and break down old red blood cells that pass through the sinusoids of the liver. In addition, due to its peroxidase activity in the cytoplasm, it can also degrade bacterial and other microorganism walls.
To modulate liver homeostasis in the liver:
Kupffer cells can control ion homeostasis by using regulatory signals to express hepcidin.
Hepcidin is a peptide hormone that mainly controls the entry of iron into the circulatory system of mammals. Interestingly, when hepcidin levels increase (especially during inflammation or immune response), serum iron and iron absorption in the intestine decrease.
To regulate antiviral immunity during hepatitis B and C infections:
They can also inhibit the growth of viral infections in the liver, particularly hepatitis B and C infections.
Together with other macrophages, they contribute to tissue damage of the infected body part. Apart from that, they also regulate fibrosis (thickening of connective tissue), cirrhosis (scarring of the liver), and hepatocellular carcinoma (abnormal growth of liver cells), which occur during hepatitis.
Anatomy of the Kupffer cell
These cells are too tiny to be observed individually using a compound microscope. Often, electron microscopy is used to keep the elongated Kupffer cell to a wormlike or starlike body.
Like any other cell, they have several organelle distributions and arrangements. Some of them are described below:
- Plasma membrane: They have plasma membranes with extensions such as microvilli, pseudopodia, filopodia, and lamellipodia. These structures are what give the appearance of a star to the worm.
- Cytoplasm: They are giant sinusoidal cells. Therefore, their cytoplasmic volume is generally dense and considerable.
- Golgi bodies: In the Kupffer cells, it is observed that the Golgi bodies are grouped near the nucleus. Golgi bodies are involved in vesicles’ secretion and intracellular transport in the cell.
- Rough endoplasmic reticulum: Known as the organelle responsible for synthesizing ribosomes (for protein synthesis), rough ER is very abundant in Kupffer cells.
- Nucleus: Like most animal cells, they contain only one seat. Their hearts are mostly oval form and have euchromatin finely distributed. It is the nucleus that contains the genetic information responsible for the expression of the traits.
- Other organelles: Other organelles such as free ribosomes (for the synthesis of proteins), mitochondria (for the production of ATP / energy), and microtubules (for the transport of other organelles) disperse in the cytoplasm.