Dynamics of the splenic innate-like CD19 +CD45R lo cell population from adult mice in homeostatic and activated conditions

In the adult spleen, CD19 +CD45R -/lo (19 +45R lo) lymphocytes of embryonic origin exist as a distinct population to that of the conventional B cell lineage. These cells display a plasmablast phenotype, and they spontaneously secrete IgG1 and IgA, whereas the bone marrow population of 19 +45R lo cells contains B1 progenitors. In this study, we show that 19 +45R lo cells are also present in Peyer's patches and in the spleen throughout the life span of wild-type mice, beginning at postnatal day 7. Although this population is heterogeneous, the surface phenotype of most of these cells distinguishes them from follicular, transitional, marginal zone, and B1 cells. In CBA/CaHN mice, few 19 +45R lo cells were detected at postnatal day 7, and none was observed in the adult spleen. Splenic 19 +45R lo cells exhibited homeostatic BrdU uptake in vivo and actively transcribed cell cycle genes. When transferred to immunodeficient RAG2 -/-γchain -/- recipient mice, 19 +45R lo cells survived and differentiated into IgG1- and IgA-plasma cells. Moreover, in vitro stimulation of splenic 19 +45R lo cells with LPS, CpG, BAFF/IL4, and CD40/IL4 induced cell proliferation, IgG1/IgA secretion and the release of IL-10, suggesting a potential immunoregulatory role for this subset of innatelike B cells.Peer Reviewe