GARP stands for Glycoprotein A Repetitions Predominant. It belongs to the leucine-rich repeat protein family and is also known as LRRC32. It is an 80 kD type I transmembrane protein. The gene sequence is only found in vertebrates, and human GARP shares 80% amino acid identity with mouse and rat GARP.
GARP presumably plays a large role in embryogenesis, since it is widely expressed across a broad range of tissue types during development. The R395W mutation is associated with Usher syndrome type I, which results in congenital deafness, vestibular dysfunction, and blindness.
In the adult, GARP is expressed predominantly by megakaryocytes, platelets, placenta, lung, kidney, and skeletal muscle. It was discovered that GARP is selectively expressed on naturally activated FOXP3+ Treg cells, providing a valuable marker for this cell type. There seems to be some interplay between GARP and FOXP3, such that expression of one influences the expression of the other. GARP also binds to latent TGF-beta on the cell surface via LAP, effectively controlling the activation of latent TGF-beta by keeping it sequestered to the cell surface. As such, GARP is involved in suppression and modulation of the immune response.
Transcript levels of GARP are also high in various cancers, such as squamous cell carcinoma, colorectal cancer, breast cancer, ovarian carcinoma, and prostate cancer. Because recombinant soluble GARP (sGARP) can bind to recombinant latent TGF-beta, and shows suppressive bioactivity in vitro, there is an intriguing possibility that the soluble form may exist naturally, and could be a biomarker for various cancers or autoimmune conditions.
BioLegend's LEGEND MAX(TM) Human Soluble GARP/LRRC32 ELISA Kit is a Sandwich Enzyme-Linked Immunosorbent Assay (ELISA) with a 96-well strip plate that is pre-coated with a monoclonal capture antibody. This kit specifically quantitates human soluble GARP/LRRC32 from cell culture supernatant, serum, plasma and other biological fluids. It is analytically validated with ready-to-use reagents.