Riments showed very low levels of IgM secretion, ranging from 1 to 57 ng/106cells/h, which corresponds to less than 5 (mean: 2 62 ) of total Ig secretion. Therefore, more than 95 of secretion was related to switched-memory B lymphocytes. Except for samples e and 
h, which had IgA secretion rates of 25?30 of total secretion, IgG secretion was predominant with more than 87 of all Ig secreted (mean 90 68 ). IgG’s secretion rates ranged from 200 to 1000 ng/106 cells/h (Fig. 3A). The mean secretion rates for 1676428 IgG, IgA and IgM were 6186321 ng/106 cells/h, 53647 ng/106 cells/h and 17621 ng/106 cells/h, respectively (Fig. 3B), showing a very similar evolution in the differentiation status for all the tested samples.Secreted IgG Contains All Four Gamma IsotypesThe secretion rates for the gamma isotypes were determined using specific ELISA tests (Fig. 3 C and D). The secretion rates varied from 160 to 460 ng/106cells/h for IgG1, from 39 to 199 ng/106cells/h for IgG2, from 9 to 66 ng/106cells/h for IgG3 and from 1 to 83 ng/106cells/h for IgG4 (Fig. 3 C). According toIn vitro Generated IgG are Weakly Self-reactiveThe protein microarray assay was used to determine whether or not the in vitro generated IgG showed self-reactivity [28]. A pool of culture supernatants from 13 independent experiments, which displayed a polyclonal pattern (Fig. 4B) and which was constituted of 25837696 75 IgG, was 
probed on 9484 human peptides. A total ofLarge-Scale Expansion of Human B LymphocytesFigure 4. Switched-memory B lymphocytes secrete polyclonal IgG. IgG’s polyclonality was determined by IEF for experiments a to j. A representative pattern is presented in panel A. (A) Briefly, IEF standard (Std), IVIg, a human monoclonal IgG (mAb) and culture supernatants from experiment a sampled on days 16, 21, 30, 41 and 49 are shown. This polyclonal IEF pattern is similar for the ten independent cultures presented in Fig. 1. (B) IEF pattern was determined for the cumulated supernatants of the three experiments presented in Fig. 5 as well as the pooled supernatants of 13 representative experiments. As mentioned above, Std, IVIg and mAb were used as Z-360 chemical information controls and a sample from a healthy human serum was also used for the same Benzocaine web purpose. For all samples in (A) and (B), analyses were done on 100 ng IgG per well. doi:10.1371/journal.pone.0051946.gtargets were spotted by the IgG preparation (Table 1), which represents 0.2 of the 9484 peptides tested. As a comparison, the screening of a commercial IVIg using the same protein array assay reacted with 67 targets [29] including 10 of those listed in Table 1 as indicated (#). Besides, when using switched-memory B lymphocytes, obtained from participants recently vaccinated for hepatitis B, we detected IgG specific reactivity for hepatitis B surface antigen in our culture supernatants (data not shown).from 3 independents experiments and obtained similar IgE concentrations, namely 13.362.2 mg/mL, 5.060.2 mg/mL and 7.460.5 mg/mL.DiscussionThe present study established long-term culture conditions enabling the generation of large quantities of human B lymphocytes. The resulting pool of human B lymphocytes, which could be enlarged by up to 106-fold after 45 to 50 days, were polyclonal and viability was still very good (.80 ). These populations included proportions of gamma isotypes as well as kappa/lambda ratios that were comparable to those observed in human blood [26,27,30]. Overall, this in vitro culture model allowsIn vitro Expanded Switched-me.Riments showed very low levels of IgM secretion, ranging from 1 to 57 ng/106cells/h, which corresponds to less than 5 (mean: 2 62 ) of total Ig secretion. Therefore, more than 95 of secretion was related to switched-memory B lymphocytes. Except for samples e and h, which had IgA secretion rates of 25?30 of total secretion, IgG secretion was predominant with more than 87 of all Ig secreted (mean 90 68 ). IgG’s secretion rates ranged from 200 to 1000 ng/106 cells/h (Fig. 3A). The mean secretion rates for 1676428 IgG, IgA and IgM were 6186321 ng/106 cells/h, 53647 ng/106 cells/h and 17621 ng/106 cells/h, respectively (Fig. 3B), showing a very similar evolution in the differentiation status for all the tested samples.Secreted IgG Contains All Four Gamma IsotypesThe secretion rates for the gamma isotypes were determined using specific ELISA tests (Fig. 3 C and D). The secretion rates varied from 160 to 460 ng/106cells/h for IgG1, from 39 to 199 ng/106cells/h for IgG2, from 9 to 66 ng/106cells/h for IgG3 and from 1 to 83 ng/106cells/h for IgG4 (Fig. 3 C). According toIn vitro Generated IgG are Weakly Self-reactiveThe protein microarray assay was used to determine whether or not the in vitro generated IgG showed self-reactivity [28]. A pool of culture supernatants from 13 independent experiments, which displayed a polyclonal pattern (Fig. 4B) and which was constituted of 25837696 75 IgG, was probed on 9484 human peptides. A total ofLarge-Scale Expansion of Human B LymphocytesFigure 4. Switched-memory B lymphocytes secrete polyclonal IgG. IgG’s polyclonality was determined by IEF for experiments a to j. A representative pattern is presented in panel A. (A) Briefly, IEF standard (Std), IVIg, a human monoclonal IgG (mAb) and culture supernatants from experiment a sampled on days 16, 21, 30, 41 and 49 are shown. This polyclonal IEF pattern is similar for the ten independent cultures presented in Fig. 1. (B) IEF pattern was determined for the cumulated supernatants of the three experiments presented in Fig. 5 as well as the pooled supernatants of 13 representative experiments. As mentioned above, Std, IVIg and mAb were used as controls and a sample from a healthy human serum was also used for the same purpose. For all samples in (A) and (B), analyses were done on 100 ng IgG per well. doi:10.1371/journal.pone.0051946.gtargets were spotted by the IgG preparation (Table 1), which represents 0.2 of the 9484 peptides tested. As a comparison, the screening of a commercial IVIg using the same protein array assay reacted with 67 targets [29] including 10 of those listed in Table 1 as indicated (#). Besides, when using switched-memory B lymphocytes, obtained from participants recently vaccinated for hepatitis B, we detected IgG specific reactivity for hepatitis B surface antigen in our culture supernatants (data not shown).from 3 independents experiments and obtained similar IgE concentrations, namely 13.362.2 mg/mL, 5.060.2 mg/mL and 7.460.5 mg/mL.DiscussionThe present study established long-term culture conditions enabling the generation of large quantities of human B lymphocytes. The resulting pool of human B lymphocytes, which could be enlarged by up to 106-fold after 45 to 50 days, were polyclonal and viability was still very good (.80 ). These populations included proportions of gamma isotypes as well as kappa/lambda ratios that were comparable to those observed in human blood [26,27,30]. Overall, this in vitro culture model allowsIn vitro Expanded Switched-me.