Abstract

A type I trans membrane protein known as the polymeric immunoglobulin receptor (pIgR) is primarily made up of an intracellular area, a trans membrane region, and an extracellular region. Additionally, the repeating immunoglobulin-like (Ig-like) domains in the extracellular domain of pIgR increase in number with vertebrate evolution, from four in birds, amphibians, and reptiles to five in mammals [1]. It’s interesting to note that while pIgR can be expressed in the liver, respiratory system, intestines, and other organs, there are clear differences in pIgR expression levels between the same sites and different animals, as well as between different organs and physiological states within the same animal. The level of pIgR expression is significantly higher in the rodent liver than in the respiratory tract, and it is decreased or nonexistent in conditions like human lung cancer and rectal cancer. For instance, pIgR expression is higher in the mouse small intestine after weaning than before, whereas it only appears in the small intestine of rats after weaning [2].