Paneth Cells are one of four principal cell types found in the epithelium of the small intestine; the other three are the goblet cell, enterocyte, and enteroendocrine cell. Paneth cells may also be found in the cecum and appendix, although sporadically.
These cells are identifiable microscopically by their location just below the intestinal stem cells in the intestinal glands. and the large eosinophilic refractile granules that occupy most of their cytoplasm. These granules consist of several antimicrobial compounds and other compounds that are important in immunity and host-defense. When exposed to bacteria, Paneth cells secrete some of these compounds into the lumen of the intestinal gland, aiding in the maintenance of the gastrointestinal barrier.
Unlike the other epithelial cells that form near the bottom of the intestinal glands, Paneth cells migrate downward from the stem cell region and settle just adjacent to it. The close relationship with the stem region suggests Paneth cells are important in defending the gland stem cells from microbial damage, though this is not clearly known.
Paneth cells are continuously replenished, as they are important for the long-term maintenance of the intestinal epithelium. Paneth cells secrete various defense molecules, of which the principal kind are called alpha-defensins. These molecules (or peptides) have hydrophobic and positively-charged domains that can interact with phospholipids in cell membranes. This structure allows defensins to insert membranes, where they interact with one another to form pores that disrupt membrane function, leading to cell lysis. Due to the higher concentration of negatively-charged phospholipids in bacterial than vertebrate cell membranes, defensins favorably bind to and disrupt bacterial cells, sparing the cells they are functioning to protect.
The Paneth cells secrete defensins when exposed to bacteria or bacterial products such as lipopolysaccharide, muramyl dipeptide and lipid A.
Paneth cells also secrete lysozyme, tumor necrosis factor-alpha, and phospholipase A2. Lysozyme and phospholipase A2 both have clear antimicrobial activity. This battery of secretory molecules gives Paneth cells a potent arsenal against a wide array of agents, including bacteria, fungi and even some viruses.
Paneth cells are named for Austrian physician Joseph Paneth (1857-1890).
Image Caption: Human Paneth cells. Credit: Jpogi/Wikipedia