“…All culture supernatants from single-cell cultured memory B cells used in this study were generated and reported as part as a previous study (see Sokal et al, 2021b). Briefly, single B cells were sorted in 96-well plates containing MS40L lo cells expressing CD40L (kind gift from G. Kelsoe, Crickx et al, 2021;Luo et al, 2009). Cells were co-cultured at 37 C with 5% CO2 during 21 or 25 days in RPMI-1640 (Invitrogen) supplemented with 10% HyClone FBS (Thermo Scientific), 55 mM 2-mercaptoethanol, 10 mM HEPES, 1 mM sodium pyruvate, 100 units/mL penicillin, 100 mg/mL streptomycin, and MEM non-essential amino acids (all Invitrogen), with the addition of recombinant human BAFF (10 ng/ml), IL2 (50 ng/ml), IL4 (10 ng/ml), and IL21 (10 ng/ml; all Peprotech).…”