Sustained Secretion of Immunoglobulin by Long-Lived Human Tonsil Plasma Cells

Abstract

Immunoglobulin-secreting cells comprise both short-lived proliferating plasmablasts and long-lived nonproliferating plasma cells. To determine the phenotype and functional activity of Ig-secreting cells in human lymphoid tissue, we used a tonsillar organ culture model. A significant proportion of IgA and IgG secretion was shown to be mediated by long-lived, nonproliferating plasma cells that coexpressed high levels of CD27 and CD38. The presence of such cells was further corroborated by the finding of enhanced expression in the CD19(+) B-cell population of XBP-1, IRF-4, and particularly Blimp-1 genes involved in the differentiation of plasma cells. Intact tissue seemed to be necessary for optimal functional activity of plasma cells. A strong correlation was found between concentrations of interleukin-6 and IgA or IgG, but not IgM, in culture supernatants suggesting a role for interleukin-6 in the survival of long-lived plasma cells. Taken together, the present study demonstrates that human lymphoid tissue harbors a population of nonproliferating plasma cells that are dependent on an intact microenvironment for ongoing Ig secretion.