LAIR1 (Leukocyte-associated immunoglobulin-like receptor 1) is an immune checkpoint receptor that is broadly expressed on a variety of hematopoietic cells, including T cells, B cells, and natural killer cells. LAIR1 modulates the homeostatic functions of monocytes and interstitial lung macrophages by binding to collagen. LAIR1 contains immunoreceptor tyrosine-based inhibitory motifs (ITIMs). When it binds to its ligand, it can recruit Src homology phosphatase-1 (SHP-1), thereby transmitting an inhibitory signal that reduces immune responses. LAIR1 is expressed on immunosuppressive myeloid cells in the tumor microenvironment, supporting their immunosuppressive activity, which may contribute to tumor development. LAIR1 may also be involved in immune imbalances in autoimmune diseases such as rheumatoid arthritis and systemic lupus erythematosus. Its absence may lead to abnormal cell activation and uncontrolled inflammatory responses. LAIR1 is differentially expressed in certain hematopoietic and non-hematopoietic tumors, potentially participating in their development.
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