A non-stimulatory monoclonal antibody against the inhibitory immunoreceptor LAIR-1

The human leukocyte-associated Ig-like receptor (LAIR) family contains two members: LAIR-1 (CD305) and LAIR-2 (CD306). Among them, LAIR-1 is a transmembrane glycoprotein bearing two intracellular immunoreceptor tyrosine-based inhibition motifs (ITIM) and LAIR-2 is soluble. Both molecules bind collagen and LAIR-2 has higher affinity than LAIR-1. LAIR-1 can mediate strong inhibitory signal but the functions of leukocytes expressing LAIR-1 are unclear because of the absence of an effective method to isolate them with resting status. In this study, we generated a monoclonal antibody (MAb) by immunizing BALB/c mice with the recombinant LAIR-2-GST fusion protein, which we termed 3G4. The subclass of 3G4 was identified as IgG1. Specificity analysis by Western blotting demonstrated 3G4 could react with both LAIR-1 and LAIR-2. Unlike another LAIR-1-specific MAb (9.1C3), 3G4 did not inhibit the lysis of target cells P815 by NK cells in a redirected cytotoxicity assay. Preincubation of LAIR-1-transfected K562 cells with 3G4 mildly prevented the binding of LAIR-1 to collagens I and III in a dose-dependent manner. Taken together, the novel MAb 3G4 provides a useful tool to isolate LAIR-1-positive cells without changing their resting state for further application.