Introduction to Long-Term Cultures of Normal B Lymphocytes
Over the last 15 years, the pathways involved in the maturation of cells within the B lymphocyte lineage have become increasingly well understood. It is now apparent that sIg+ B cells derive from a large pool of immature precursors that may constitute 25% or more of normal adult bone marrow (1). Their progeny are seeded to peripheral lymphoid tissues at rates sufficient to replace 5% to 10% of all mature B cells each day (2, 3). Upon reaching the periphery, the majority of immunocompetent cells die rapidly with a T 1/2 = 24 hr (4, 5) unless they are salvaged by antigen-specific or nonspecific stimuli. Even with continuing stimulation, it appears that the life span of these rescued cells would not exceed that required for an additional 30 to 50 rounds of replication (6). Within the broadly-sketched outline of B cell growth and clonal senescence, there exists a multitude of sequential decision points that contribute to the extensive phenotypic and functional heterogeneity observed within the pool of peripheral B lymphocytes.
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