Purified FL B cells carrying (A) WT (n = 5) or (B) mutant (n = 6) ATP6V1B2 were cultured in dialyzed serum–supplemented RPMI 1640 medium containing either 100% leucine or, depending on the availability of sufficient cells, reduced leucine concentrations (0%, 6.25%, 12.5%, and 25%). FL B cells were cultured, and the cell number and fraction of living cells were determined out to 5 days. (C and D) Summary of the results of the individual data displayed in A and B. Shown is the number of viable cells at various leucine concentrations, divided by the number of living cells at 100% leucine concentration. Significance levels are indicated by asterisks: *P < 0.05, **P < 0.01, and ***P < 0.001, compared with results for WT at the same time point (comparisons were done with a t test). Data represent the SD.