Pattern recognition receptors (PRRs) are crucial components of the innate immune system, responsible for detecting pathogens and initiating immune responses. These receptors recognize pathogen-associated molecular patterns (PAMPs), which are conserved molecular structures found in a variety of pathogens, including bacteria, viruses, fungi, and parasites. By identifying these patterns, PRRs can rapidly trigger immune responses to combat infections.
There are several types of PRRs, each with specific roles and locations within the immune system. Toll-like receptors (TLRs) are perhaps the most well-known PRRs and are found on the surfaces of immune cells like macrophages and dendritic cells. They recognize a wide range of PAMPs, such as bacterial lipopolysaccharides and viral RNA, and activate signaling pathways that lead to the production of inflammatory cytokines and other immune responses.
Another important class of PRRs is the NOD-like receptors (NLRs), which are located within the cytoplasm of cells. NLRs detect intracellular pathogens and can trigger the formation of inflammasomes, protein complexes that activate inflammatory responses and promote the release of cytokines like interleukin-1β.
C-type lectin receptors (CLRs) and RIG-I-like receptors (RLRs) are additional types of PRRs. CLRs are primarily involved in recognizing fungal components, while RLRs detect viral RNA within the cytoplasm, leading to antiviral responses.