[From the Discussion section of the full text.]
The transitional immature B-cell subset (CD24highCD38high) has been proposed as the main producer of IL-10 by the B-cell population [46].
[Prof. @Jonathan Edwards may have been referring to that work when he said, "this is just a phase B cells go through early in development."] However, in another study, the IL-10-secreting cells were predominantly found in the CD24highCD27+ B-cell population [48].
[And that is the study @Jon_Tradicionali cited.] Considering that a consensus about CD24 expression seemed to emerge as a hallmark for IL-10-secreting human B cells, we monitored expression of this surface marker upon incubation of human B cells with
L. infantum amastigotes. We report herein that the parasite leads to a significant reduction in the expression of CD24 (Fig. 4B), indicative of B-cell activation [102,103], with no effect on CD38 (Fig. 4C). Altogether, these results suggest that the phenotype of IL-10-secreting B cells following incubation with
L. infantum is different from those that were described previously. In a related set of experiments, we studied different purified B-cell subsets (i.e. CD24+, CD27+ and CD38+) and surprisingly, only the CD27-negative B-cell subpopulation responded to the parasite by producing IL-10 (Fig. 5A). Furthermore, we were able to reveal the importance of CD24+cells, but not CD38+, for the secretion of IL-10 by B cells in response to
L. infantum amastigotes (Fig. 5B). This suggests a quite different IL-10-secreting B-cell subset from those that were previously described both in human in vitro and murine in vivo models [41,43,46,48]. While it is assumed that phenotypic characteristics of IL-10-producer cells might differ according to the stimuli to which they are exposed, this CD24+CD27- human B-cell subpopulation seems to respond to
L. infantum amastigotes by secreting high levels of IL-10.