All 3 tyrosines in the cytoplasmic tail of FcRL4 are necessary for its inhibitory function. (A) Amino acid sequence of the cytoplasmic domain of FcRL4, in the region containing the 3 tyrosine motifs (in blue) with the tyrosines mutated to phenylalanine in red. (B) CD69 NMFI after BCR cross-linking in cell lines stably expressing either the wild-type or mutant of FcRL4s. Data shown are from 10 independent experiments and are expressed as means ± SD. P values between 2 groups were obtained from unpaired, 2-tailed Student t test.