Pattern recognition receptor

The term "pattern recognition receptors" is used to describe a class of receptors. Such receptors play an important role in the innate (non-specific) immune defense. PPRs recognize certain bacterial molecular structures that do not occur in humans but are constantly present in various bacteria. These include, for example, various cell wall components such as lipoproteins, lipoteichoic acid, peptidoglycans or flagellins. These structural elements are called pathogen-associated molecular patterns or PAMPs. Upon recognition of these structural elements by the PPRs, the PPRs are activated and in turn initiate a "first step" immune response.

In this process cytokines are released.

Interleukin-1beta plays a central role in this process. The regulation of IL-1 release is carried out by inflammasomes.

Due to structural similarities, the cell-bound PRRs are divided into several receptor families:

• Surface receptors:
  • Scavengerreceptors(scavenger): Scavenger receptors enable macrophages to phagocytose pathogens. 9 different receptors were found. They are classified on the basis of best. They are divided into different classes (SR-A, -B, -C etc.) based on their structural characteristics.
  • C-type lectin receptors: These are involved in phagocytosis. By means of a calcium-dependent recognition of certain sugar compounds, they bind to various pathogens such as bacteria, viruses, fungi and parasites.
  • Toll-like receptors (Toll from the German term "toll"): They recognize different components of bacteria, viruses, fungi and protozoa and trigger a strong activation of the immune cells.
• Intracellular PRRs:
  • NOD-like receptors (NLRs): Known are > 20 variants. They recognize bacteria and induce an activation of immune cells by mobilization of the transcription factor NF-kappaB and the interleukin-1 activating enzyme caspase-1.
  • RIG-I-like proteins: The three known members of this family (including the eponymous RIG-I) have RNA helicase activity and are involved in the recognition of viruses. They trigger an activation of immune cells by the transcription factors of the IRF family and NF-kB.

1. Sameer AS et al.(2021) Toll-Like Receptors (TLRs): Structure, Functions, Signaling, and Role of Their Polymorphisms in Colorectal Cancer Susceptibility. Biomed Res Int 2021:1157023. doi: 10.1155/2021/1157023.