Despite the important role immunoglobulin G (IgG)-secreting plasma cells play in memory immune responses, the differentiation and homeostasis of these cells are not completely understood. Here, we studied the differentiation of human IgG-secreting cells ex vivo and in vitro, identifying these cells by the cellular affinity matrix technology. Several subpopulations of IgG-secreting cells were identified among the cells isolated from tonsils and bone marrow, particularly differing in the expression levels of CD9, CD19, and CD38. CD38 low IgG-secreting cells were present exclusively in the tonsils. A major fraction of these cells appeared to be early plasma cell precursors, as upon activation of B cells in vitro, IgG secretion preceded up-regulation of CD38, and on tonsillar sections, IgG-containing, CD38 low cells with a plasmacytoid phenotype were found in follicles, where plasma cell differentiation starts. A unitary phenotype of migratory peripheral blood IgG-secreting cells suggests that all bone marrow plasma cell populations share a common precursor cell. These data are compatible with a multistep model for plasma cell differentiation and imply that a common CD38 low IgG-secreting precursor gives rise to a diverse plasma cell compartment.

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Polycrystalline and mosaic bicrystalline titanium films were subjected to steep heating/cooling rate of 1011∕108Ks−1 by laser pulsing. The induced phase transformations were followed by imaging and diffraction with a dynamic transmission electron microscope on the time scale of nanoseconds. On heating the film up to near the melting point with a 6-ns laser pulse, the low-temperature hcp phase transformed to the high-temperature bcc phase, with a nucleation rate of 1025m−3s−1 and a crystal-growth velocity of about 1000ms−1. Quenching of molten Ti first produced the bcc phase, which in turn transformed to the hcp phase within a few microseconds. Thus, hcp-bcc transformations occur in Ti, even at the above high thermal rates. They are martensitic and not diffusion limited as claimed for transformations at low thermal rates.

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