A proportion of the CD20+CD27–CD43hi cells were CD3–CD19+; this is in line with other, more recent reports showing that some CD20+CD27+CD43hi cells could be plasmablasts [29]. Finally, previous work has addressed the possibility that activated conventional memory B2 cells could also up-regulate CD43, and thus further contaminate the B1 population by analysing expression of activation markers such as CD69 and CD70

on the population [12]. Work in this study agreed with previous findings, with < 3% of the CD27+CD43lo–int subpopulation expressing CD69 on their surface (data LEE011 chemical structure not shown). Controversy exists regarding the measurement of the CD20+CD27+CD43lo–int cell subset percentage in the peripheral blood of healthy controls. This study found a median value of 4·1% of all CD20+ B cells and 18·7% of all CD27+ B cells to be CD20+CD27+CD43lo–int. This value differs from the previous reported values of 12·7% of all CD20+ cells and approximately 20% of all CD27+ B cells in healthy controls find more [12]. However, the age range of these controls is unknown. A subsequent report gave a range of 1–9% of all CD20+ cells to be putative B1 B cells in a further cohort healthy controls although, again, no median age was given for this cohort [30]. This is similar to other groups who reported a value of 2·2% of all CD20+ B cells and a range of 1–25·5% of all CD20+ cells to be

human B1 B cells [29, 31]. All these values indicate that in the periphery, putative human B1 B cells appear to make up a minor proportion of the circulating B cell population, suggesting that they may behave similarly to murine B1 cells which are predominantly resident in peripheral tissues, in particular the peritoneal cavity [32]. A moderate correlation of CD27+CD43lo–int cell percentage with age was found in this study, with older individuals possessing a smaller

percentage compared to younger individuals, correlating with previous reports that also report a decline with age [12, 29, 31]. These findings highlight the necessity for median age statistics to be known for any given cohort, Oxymatrine as this can have an impact on discrepancies seen between study groups. Of the CD20+CD27+CD43lo–int cells, 11·5% expressing CD5 were observed in this study. This conflicts with previous work which describes 75% of ‘B1 cells’ to be CD5-positive [12]. Although such a high CD5 positivity could be caused by a potential T cell contamination, further data provided by their study showed that this is unlikely, as their ‘B1 cell’ population co-expressed almost exclusively other typical B cell markers (CD19), as shown by confocal microscopy [30]. We found a median surface IgM expression percentage of 64·4% in the CD27+CD43lo–int putative B1 B cell subpopulation in healthy controls. This probably indicates that some cells in this population have undergone class switching [33].