(a,d) Four subset no. 4 CLL-derived clonotypic BcR IGs (CLL183, CLL240, P103, P907) were expressed in TKO cells reconstituted with a OHT-inducible variant of SLP-65 (ERT2-SLP65), and IG surface expression was assessed. (b,e) Intracellular Ca2+ influx on induction of SLP65 function with OHT. While the wild-type (WT) receptors lead to Ca2+ influx, neither the Glu16HAla (FR) nor the Arg106HAla/Tyr107HAla (CDR3) mutants signalled on OHT addition. (c,f) All receptors expressed in the TKO cells were competent for signalling, and induced Ca2+ influx when crosslinked with an anti-κ-chain antibody. Addition of the stimuli is indicated by black arrows.