PIR (gene)

PIR, often referring to the Paired Immunoglobulin-like Receptor gene, encodes a transmembrane protein belonging to the immunoglobulin superfamily. PIRs are primarily expressed on immune cells, including B cells, macrophages, dendritic cells, and mast cells, and function as receptors involved in regulating immune responses.

PIR genes are characterized by multiple immunoglobulin-like domains in their extracellular region. These domains are responsible for binding to various ligands, leading to signaling events within the cell.

The precise ligands for all PIR family members are not fully characterized. However, some PIRs are known to interact with MHC class I molecules, thereby modulating the immune response.

PIRs can act as either activating or inhibitory receptors, depending on the specific PIR isoform and the context of ligand binding. Activating PIRs typically associate with intracellular signaling molecules containing immunoreceptor tyrosine-based activation motifs (ITAMs), leading to cell activation and enhanced immune function. Inhibitory PIRs, on the other hand, associate with intracellular signaling molecules containing immunoreceptor tyrosine-based inhibitory motifs (ITIMs), resulting in suppression of immune cell activation.

The balance between activating and inhibitory PIR signaling plays a crucial role in maintaining immune homeostasis and preventing autoimmunity. Dysregulation of PIR expression or signaling has been implicated in various autoimmune and inflammatory diseases.

Different species may have varied numbers and types of PIR genes. Rodents, for example, have a relatively large and diverse family of PIR genes, reflecting the evolutionary adaptation of their immune system.