Ligation of human Fc receptor like‐2 by monoclonal antibodies down‐regulates B‐cell receptor‐mediated signalling

B‐cell antigen receptor (BCR) signalling and its regulation through negative and positive regulators are critical for balancing B‐cell response and function. Human Fc receptor like‐2 (FCRL2), a member of the newly identified FCRL family, could influence B‐cell signalling due to possession of both immunoreceptor tyrosine‐based activation and inhibitory motifs (ITAM and ITIM). Since the natural ligand of FCRL2 has not been identified, we generated FCRL2‐specific monoclonal antibodies (mAbs) and employed them to investigate the influence of FCRL2 stimulation on BCR signalling in an FCRL2‐expressing B‐cell line. Two anti‐FCRL2 mAb‐producing hybridoma clones (5A7‐E7 and 3D8‐G8) were selected. None of the mAbs displayed any cross‐reactivity with the other members of the FCRL family including recombinant FCRL1, ‐3, ‐4 and ‐5, as tested by FACS and ELISA techniques. Engagement of the FCRL2 by these mAbs resulted in significant inhibition of BCR signalling mediators such as calcium mobilization and phosphorylation of the mitogen‐activated protein kinases Erk, p38 and Jnk. These findings indicate that the FCRL2 ITIM motifs are functional and the anti‐FCRL2 mAbs may mimic the natural ligand of FCRL2 by induction of inhibitory signals in B cells.