Transfer of small resting B cells into immunodeficient hosts results in the selection of a self-renewing activated B cell population

We studied the role of bone marrow B cell production in the renewal of peri pheral B cells and the feedback mechanisms that control the entry of newly formed B cells into the peripheral B cell pools. When resting lymph node B cells are injected into B cell-deficient hosts, a fraction of the transferr ed cells expands and constitutes a highly selected population that survives for prolonged periods of time by continuous cell renewal at the periphery. Although the number of donor B cells recovered is low, a significant fract ion shows an activated phenotype, and the serum immunoglobulin (Ig)M levels are as in normal mice. This population of activated B cells is resistant t o replacement by a new cohort of B cells and is able to feedback regulate b oth the entry of newly formed B cells into the peripheral pool and terminal differentiation. These findings suggest that peripheral B cell selection f ollows the first come, first served rule and that IgM-secreting cells are g enerated from a pool of stable activated B cells with an independent homeos tasis.