Pattern recognition receptors (PRRs) are specialized proteins that are found on the surface of various immune cells, including macrophages, dendritic cells, and mast cells. They are responsible for recognizing pathogen-associated molecular patterns (PAMPs), which are specific molecular patterns found on the surface of pathogens.
PRRs are a key component of innate immunity, as they allow immune cells to recognize and respond to a wide range of pathogens without the need for prior exposure. There are several different types of PRRs, including:
- Toll-like receptors (TLRs): TLRs are a family of PRRs that recognize a wide range of PAMPs, including bacterial lipopolysaccharides and viral nucleic acids.
- NOD-like receptors (NLRs): NLRs are a family of cytosolic PRRs that recognize bacterial peptidoglycans and other intracellular pathogens.
- RIG-I-like receptors (RLRs): RLRs are a family of cytosolic PRRs that recognize viral RNA.
- C-type lectin receptors (CLRs): CLRs are a family of PRRs that recognize carbohydrate structures found on the surface of fungi and other pathogens.
Once a PRR recognizes a PAMP, it triggers a signaling pathway that leads to the activation of the immune cell and the initiation of the immune response. This can include the production of cytokines, chemokines, and antimicrobial peptides, as well as the activation of phagocytosis and other immune responses.
PRRs are essential for the proper functioning of the innate immune system, and deficiencies in PRRs or their signaling pathways can lead to increased susceptibility to infections and other immune disorders. On the other hand, overactivation of PRRs can lead to chronic inflammation and autoimmune diseases. Therefore, the regulation of PRR signaling is critical for maintaining a proper balance between immunity and tolerance.